Corvette leaf springs

[culver]

I saw this on a Corvette Forum, thought I would share.

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Corvette and leaf springs. Many people are surprised to hear that the C6 Corvette uses leaf springs. This seams to conger up images of ox carts and old Ford pickups. I thought I would post my understanding of the technology with the hopes that other will post their insight.


Since 1984 the Corvette has used a transverse fiberglass composite leaf spring as part of the suspension. The C5 and C6 both have very similar double A-arm suspensions that wouldn't look out of place on any high end sports car. The only significant difference being instead of a coil over spring the Vette is using a single leaf spring. The suspension geometry and motion would be exactly the same if GM chose to use coil springs rather than the leaf. For those who might think the Corvette’s leaf spring is “outdated” technology, keep in mind that the composite leaf spring was introduced as an option in 1981 and in it’s current layout (acting as a partial anti-role bar) in 1984. It’s safe to say the coil spring is much older.


This is a picture of the C5's rear suspension.

http://www.corvettecavalry.com/exhaust/no-mufflers.jpg

The leaf is the black thing that runs from one side to the other just under the lower A arms.



A Brief History of Leaf Spring Suspension.

Excluding the Corvette I'm aware of 4 general types of leaf spring suspensions.

1. Model T style transverse leaf.

http://www.trainweb.org/toenailridge/vanradiator.jpg

This model shows the transverse leaf used on a Ford Model-T. The suspension has two lateral arms that keep the front axle perpendicular with the chassis. Lateral axle movement is controlled by the spring. This system suffers from poor control of the axle’s movements among other flaws. I’m not aware of any production car that uses this suspension type.



2. Conventional truck type, longitudinal leaf springs:

http://www.chris-longhurst.com/carbibles/index.html?menu.html&suspension_bible.html (scan down)

This is the one we all love to hate. It’s also about the only type of leaf spring suspension still in use. It’s cheep, durable and handles badly. It suffers from friction between the leaves and from poor control of the axle’s location.



3. Golf cart style transverse leaf spring:

I couldn’t find any pictures of this but it basically looks like a double A-arm where the leaf spring is one of the A-arms. The geometry is probably OK under vertical loads but lateral loads would defect the spring and cause camber changes. Not an issue for golf carts but bad for sports cars.



4. Leaf with links. There are lots of variations on this suspension

Miller Indy Roadster

http://www.scaleautoworks.com/millerphoto.jpg

http://www.scaleautoworks.com/metalMillerFQ3.jpg (the black things on top of the front axle

Jaguar MkII rear suspension (can’t find a picture)

Like #3, these suspensions uses a combination of links and the leaf spring to support the axle. The Jaguar set up looks similar to a 4 bar solid axle rear suspension except the lower link is the end of an inverted leaf spring. The other end for the leaf is attached to the chassis under the passenger compartment. The middle of the upside down (frown rather than smile) spring presses against a rubber block. The end connects to the bottom of the axle. This system offers better handling and axle control than #2 but is still suffers from friction between the leaves of the springs and compared to multi-link live axles, poor control of the axle’s location.



What makes these all the same

All of the above have several things in common. First, multi-leaf springs that suffer from friction between the leaves as the leaf flexes. Second, the inherently flexible leaf spring is being asked to work as a spring AND a suspension arm. Springs (leaf, coil, torsion etc) are good at being springs. They are bad at being other things like rigid links. In those suspension designs the spring is being asked to hold the axle and be a spring. To it’s credit, the leaf spring does this much better than a coil spring. How well would a coil spring do that job? Think of a bobble head doll.



Why is the Vette different?

First, the Vette actually has double A-arm suspension like many other high end sports cars. The A-arms are used to fully control the movement of the wheels. The only difference between the Vette and other cars with A-arms is the Vette uses a leaf to pull the lower arm down rather than a coil spring to push it down. In both cases the spring is doing what it does best, being a spring ONLY.

The other problem was friction between the leaves of a leaf spring. Well the Vette uses a single piece leaf so there is no internal friction, just like a coil spring.

So what we have is double A-arm geometry just using a different type of spring.



So why does the Vette use it

To be honest, I have no idea how GM got started with the transverse leaf spring. The used to use coils in front but in 1984 they switched too leafs front and rear. I suspect it’s a tradition they maintain for the same reason Porsche keeps their engine out back even though the platform mate Boxster moved it to the middle.



What are the advantages for the Vette?

This is an article written around the time the C4 was released. It covers a lot of the reasons why GM retained the leaf suspension

http://web.telia.com/~u60113742/misc/suspension/fiberglass_spring.gif

The big advantages are:

-It weights A LOT LESS than coil springs. One leaf replaces two coils. The two coil springs weigh 3 times as much as the one leaf. Additionally the leaf is placed at the bottom of the car. In addition to removing weight you lower the CG.

-It acts as an anti role bar. The article above explains how this works so I won’t. The advantage is you can run lighter anti-role bars because the springs are taking care of part of the job for you.

-The leaf springs never wear out. The vendor of these springs has never had to replace one due to fatigue failure. Coil springs to were out but you typically don’t notice on smaller, lighter cars. You do see it more on old, heavy Caddies and such. The improved fatigue life was really evident compared to the C3’s steel leaf spring. Thus this is an advantage over coils but not a big one.



What are the drawbacks for the Vette?

-They are expensive. We normally don’t think of leaves as the expensive suspension but in the case of the Corvette, coils would be cheaper. The Vette already has all the parts a coil sprung double A arm suspension would use. Pull the leaf off, replace the shock with a coil over and you’ve converted the Vette. Since the rest of the system is the same, the cost comes down to the price of 2 coils or one spring. Well if it was a steal leaf spring it might be cheaper (remember truck suspension is cheaper because the leaves also act as links).

[culver]

Part 2
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If it’s so good why don’t other people use it?

It’s legitimate to ask, does GM know something that Ferrari, Porsche etc don’t know or are the people at GM just being pig headed and sticking with “outdated” technology.



Street cars:

-You must design them into the car in the first place. This seams obvious but consider these springs span across the bottom of the car. In the front they have to clear the engine oil pan and in the back they have to stay out of the way of the differential. Basically, you can retro fit coils on the Vette because the mounts can be shared with the shock mounts. For the most part you can’t retrofit Corvette style leaves onto other cars because you would have to add mounts that don’t exist on the regular car.

-GM and their supplier spent a lot of time and money developing the Vette’s composite spring. Currently they are the only manufacture with the knowledge and understanding to make the springs work. On the other hand, coil springs are common and well understood. Lots of vendors can make them in a wide variety of configurations. It’s easier for the other manufactures to stick with what they know. Other manufactures would have to study the design and manufacture of composite leaf springs before they could pop them on the next Supra-NSX-Type-GT. GM did that work years ago. Toyota could certainly afford to develop their own composite springs if they wanted. The same may not be true for smaller companies like Ferrari and Porsche.

-Engineers like to stick with what they know. Lots of suspension engineers are familiar with using coil springs. They could experiment with leaves if they wanted or they could stick with coils and get the job done. See the point about undertaking a research project.

-Coils are cheaper. This automatically keeps them off lower cost cars (Miata, Civic) and cars that share platforms with lower cost siblings (Audi TT). Porsche isn’t worried about saving every last dollar but there suspension and chassis design may not allow packaging a Corvette type leaf. The same is probably true of Ferrari. Even if packaging isn’t a problem they still have to pay for tooling to make the springs. Unlike the GM who spreads that cost over 30,000 Vettes a year, Ferrari would spread that over maybe 2000 cars a year. Porsche would be somewhere in between. Conversely I can get coils made with relatively low setup cost and a cheaper per part cost. So not only would they have to spend more per car, they have to spend a lot more up front.

-Perception. Just like pushrods, the leaf spring as a stigma attached to it. The reasons for the stigma are legit (key component to heavy and typically poor handling suspension). However the reality is the sum of the older parts was the problem, not a specific part of it.



What about race cars? (this section is almost verbatim from another post of mine.

To start off, not all race cars use coil springs. Some F1 cars (Ferrari and others) use torsion springs instead. Years ago Indy and F1 cars DID use leaf springs but those days are long past.



The current design of open wheel racecars places great restrictions on suspension packaging. The Corvette’s transverse leaf spring must span from one side of the car to the other. Also, to be most effective the links between the spring and suspension arms should be under tension. This makes a bottom mount spring most effective. This packaging doesn’t work well on an open wheel car because the spring would have to pass though the gear box around the dif (or the gear box would have to be raised and hurt the car’s CG). At the front the driver’s legs would get in the way. Additionally the spring is wide and would have to extend past the body work where it would hurt the car’s aero package.



NASCAR rules dictate coil springs on the rear axle. They probably originally used leaves but given the option any car designer (modifier back in the day?) would have replaced the leaves with a multi-link set up. As I said before the multi-link offers better control of the rear suspension.



Another good reason is only a few companies understand the technology necessary to make the springs. Hypercoil is currently the top race spring manufacture. They can make very precise, matched spring pairs. The level of precise spring rate control and matching may not exist in the composite bow springs.



Coil race springs are not car specific. You select rates, diameters, length etc but you don’t have a specific spring for a specific car. If you want to order a custom spring Hypercoil will wind it to your specifications on the same machine they use for the next custom spring. A custom Porsche, Formula Ford and LMP car spring can all be made on the same machine. By the time the C6 evolves into a C6-R (they don’t start off with a production Corvette) the suspension geometry is so different that they couldn’t just mount a C6 leaf spring. It’s far too expensive to have a few custom leaf springs tooled up (you would have to buy the tooling as well as the springs) so they use readily available coil springs.



This type of universal tooling isn’t availible for the composite leaf spring. Only the Vette currently uses the spring so you are making a Vette only part. This seriously reduces the market for aftermarket composite leaf springs (still there are after market leaf springs available for the Vette). The business case for custom equipment to make Vette springs is harder to justify since it’s a smaller market.



Why don’t other cars retrofit leaf springs? Well they also don’t retrofit torsion springs despite the fact that F1 cars use them. Put simply it would be VERY difficult. The Vette was designed to have them. It has mount points under the car where the springs fit to the suspension sub frames. It’s not easy to just add that to a car that was designed to use a coil spring. All of the cars you mentioned would have to be re-engineered to add leaf springs. Replacing the factory spring with a racing is easy by comparison.



The other VERY significant reason is racers will use what they know. They will put effort into learning about new technology (torsion springs in F1) but ultimately it is too there advantage to stick with what they know.



Would the Vette be better with coil springs?

Well that depends. As I said before, there are a lot more options available in coil springs. If I want to substantially change the Vette’s spring rates then I will need to go to coils. Also, if I want to totally get rid of the Vette’s anti roll I need to dump the leaves because they provided some roll resistance.



BUT…

If for some reason I just lost my leaf spring (maybe someone stole it to make a very strong bow and arrow) and had to replace it with coils. I want the same ride quality, the same spring and roll rates etc. Basically I want the car to be the same as before but with coil springs. Assuming you didn’t change anything but the springs (same tires, shocks, ride height, same spring rate and effective roll rate, etc) the Vette would unquestionably be SLOWER with coils instead of the leaf setup. Basically if all else is equal, the coils are heavier and raise the CG of the car. One other small advantage is the shocks on the leaf sprung car will move more freely than the car with coilovers. When used as a coil over, coils impart a bending load on the shocks that cause them to bind a bit. On a street car you will never notice but on a race car it can cost a tenth of a second or so. (Hypercoil markets a pivoting spring perch to reduce the effects of side loading in coil over shocks).

Again, if I decide I really want to race I will likely dump the leaves because I have more options with coils. For a reasonable (in racing terms) price I can get custom coils made. The same isn’t true of the composite leaf spring.

[Matra et Alpine]

Excellent post and thanks for the pic.

We debated this before and nobody coudl confirm for me where the leaf runs.

The BIG issue with leaf springs is the limited movement and control. So variable rate and LONG travel is very difficult.

Also using the leaf as sprign AND anti-roll bar is not the best idea as a spring of any form is a compormise in a suspension anyway and to have it do 2 jobs and meet TWO sets of compromises is likely why others steer clear of it. BTW leafs are used in many modern small Eureopan cars, so the world does know how to do it :0

Also you chose to compare composite leaf and steel coil. You can get lightweight coils too. It's best NOT to justiofy anuthing by comparing appleas and oranges. And to suggest that the few poinds in a coil make the car slower is forgetting that the driver is present - you're talking about the weight of a good dump and decent meal :)

Can you please explain the bending the shock in a coilover , cos it doesn't :) UNLESS the coilover is operating non-perpendicular to the movement and in that case it's happening to the shock whether it has a spring on it or not :)

You recognsie the drawbacks as well and is a most informative post.

Thanks again.

[:Exige:]

interesting reading .. i know very little about cloverleafs, im more of a Mcphearson Strut man myself :)

[Matra et Alpine]

Actaully foudn out the 'vette sprign is only 8lbs, a little bit more than a dumpa nd a meal difference then :)
Still not a lot in a car weighing 3000+ lbs !!!!

[Sweeney921]

My truck has rear leaf springs, and with the combination of that and the fact that there's nearly no weight in the rear, it's easy to find yourself going sideways after hitting a bump in a corner :) . I guess that's a bad thing, but WAY more fun :) . I have no issue with the corvette having rear leafs; it shows that the engineers like to have some fun. :D

[KnifeEdge_2K1]

the corvette has leafs at all 4 corners

[Sweeney921]

the corvette has leafs at all 4 corners
really? haha that completely changes my mind

[culver]

Excellent post and thanks for the pic.

We debated this before and nobody coudl confirm for me where the leaf runs.

The BIG issue with leaf springs is the limited movement and control. So variable rate and LONG travel is very difficult.

Also using the leaf as sprign AND anti-roll bar is not the best idea as a spring of any form is a compormise in a suspension anyway and to have it do 2 jobs and meet TWO sets of compromises is likely why others steer clear of it. BTW leafs are used in many modern small Eureopan cars, so the world does know how to do it :0

Also you chose to compare composite leaf and steel coil. You can get lightweight coils too. It's best NOT to justiofy anuthing by comparing appleas and oranges. And to suggest that the few poinds in a coil make the car slower is forgetting that the driver is present - you're talking about the weight of a good dump and decent meal :)

Can you please explain the bending the shock in a coilover , cos it doesn't :) UNLESS the coilover is operating non-perpendicular to the movement and in that case it's happening to the shock whether it has a spring on it or not :)

You recognsie the drawbacks as well and is a most informative post.

Thanks again.

The coil comparison was based on the C4 when GM said they saved weight. Presumably it was a savings over production suitable coil springs.

This is a link to a document on Hyperco's website explaining the issues with coaxial spring loading on shocks:
http://www.hypercoils.com/DOC/Centralized-Spring-Load-Axis.doc
It's part of their information on their hydraulic spring perches.
http://www.hypercoils.com/Products/Hyperco-Hydraulic-Spring-Perch.aspx

Thanks for the good feedback!

[culver]

You can kind of see the spring in this picture. This is under the motor of a C5. There is a dark plastic looking thing that looks like it extends though the V of the suspension arms. That's the leaf spring. Each half holds up one corner of the car. As was mentioned in one of the links above the spring actually provides some role resistance. This allows GM to achive their desired total role rate with a smaller anti-role bar.
http://www.topflightcorvette.com/Str-1.jpg

This one is a picture of the rear suspension
http://www.topflightcorvette.com/images/manopz_suspension.jpg
The spring is the black plastic thing that runs just under and parallel to the lower A arms.

[RacingManiac]

BTW if they were to use leaf on the C5-R/C6-R it'd be more difficult to swap spring....While at the same token this technology of transverse leaf might not be beneficial in a NASCAR type of world of asymmetrical car setup as a single transverse leaf spring for 2 sides guarantees symmetrical rates....

[Matra et Alpine]

Great stuff Culver.

I'd never heard of that as an issue. Mind you a movement of 15 thous is well within the tolerances of the operation and I don't think is that relevant to a damper that is operating non-parallel as the forces initially try to bend the shock anyway.

Not sure if they're comparing like with like as competition shocks usually have a shaped cup ( most ordinary production have flat ) which supports most of the spring for it's first coil. By supporting the spring along the complete first coil and not relying I'm not sure if ti fully removes the need for there hydralic cup or not. Good stuff.

[culver]

Great stuff Culver.

I'd never heard of that as an issue. Mind you a movement of 15 thous is well within the tolerances of the operation and I don't think is that relevant to a damper that is operating non-parallel as the forces initially try to bend the shock anyway.

Not sure if they're comparing like with like as competition shocks usually have a shaped cup ( most ordinary production have flat ) which supports most of the spring for it's first coil. By supporting the spring along the complete first coil and not relying I'm not sure if ti fully removes the need for there hydralic cup or not. Good stuff.

It is admittedly a small difference. The difference between 1st and 2nd on the track is pretty much a non-issue with street cars.

[culver]

I know this is an old thread but the link below has some great pictures of the new Corvette Z06 including some very good pictures of the leaf springs.

http://www.z06vette.com/forums/showthread.php?t=80265

[Matra et Alpine]

I know this is an old thread but the link below has some great pictures of the new Corvette Z06 including some very good pictures of the leaf springs.

http://www.z06vette.com/forums/showthread.php?t=80265
Great find Culver. Those are excellent pics.
Really clear how that rear works.

I was surprised to see how narrow the two clamps are mounting the leaf.
With it so narrow, there will be a natural frequency of suspension movement which will setup a harmonic oscillation sweet-spot of wavelength equal to double the distance between the clamps. There will also be harmonics at 2, 4 and 8 times that frequency of movement.

on SOME surfaces those harmonic points will AMPLIFY the movements and worsen the handling. Does anyone have rates for the leaf ? We could then estimate those harmonics and hence KNOW when the rear will get "jiggly". I hope it doesn't' match the frequency when driving over cobblestones or we'll see lots of Vettes smashed on Edinburgh streets :) { If only we saw ANY Vettes in Edinburgh :( }

Could be an opportunity for an additional damper on the centre section of the spring. Wouldn't need to be big, I think even a bike steering damper might introduce enough. Otherwise when setting the suspension ratings the mechanics going to HAVE to compromise to use the main dampers to control it :(

[culver]

While I could see the harmonic issue, I don't think it will be a big deal.
1st. Remember that almost all cars already have a torsion spring between the left and right suspensions. So any issues with cross talk would to some degree be present in conventional systems.

2nd. The spring is a composite. I would assume it has some self damping properties but I have no idea what it's natural frequency is relative to say a metal spring. I'm also not sure what frequency range would be important to consider. For race car dampers the engineers are really concerned with shock velocities around 1"/sec. I assume the natural frequency of any suspension parts would be much higher.

3rd. It has rubber mounts at each end and I think at the points where it mounts to the chassis as well. These would tend to dampen vibrations.

[SlickHolden]

My brother was in a Holden Crewman with leaf springs rear, He told me if he took his cup of tea he wouldnt need a spoon;)
I remember the old V6 Holden had and no matter how many times that engine got a upgrade they still compared it to the old Buick V6 in the 60's. No matter how far it came along.

[Matra et Alpine]

While I could see the harmonic issue, I don't think it will be a big deal.
1st. Remember that almost all cars already have a torsion spring between the left and right suspensions. So any issues with cross talk would to some degree be present in conventional systems.
no, it works in an entirely differnet fashion.
An anti-roll bar is NOT restrained at the mountinf points, so when one suspension wheel moves up the bar is twistsed ADN TURNS IN THE MOUNTINGS to impart a force to the other side. Yes there is still a harmonic issue but NOW it is at wavelength harmonics of the length of the COMPLETE bar. And as it is NOT require to act as a sprign it is usually torsinoally VERY stiff and hence very HIGH natural frequency beyond the expected movements - because you are loking at the rate of change BETWEEN the wheels NOT between wheel and chassis.

The 'vette spring issue is that it's harmonics are at a much shorter wavelenght/higher rate.
The spring does not TWIST it bends, the bend is perpendicular to the mounting points, so it's not imparting directly to the other side.
As a wheel drops, the INNER section of the spring will go UP, hence imparting a downward force to the other side. So it performs TWO functions.


2nd. The spring is a composite. I would assume it has some self damping properties but I have no idea what it's natural frequency is relative to say a metal spring. I'm also not sure what frequency range would be important to consider. good point on it being composite, but I can't see how they can build in a DAMPING property for bend, vibration yeah, sure, but bend ?? Because IF they build it in to supres the natural frequency AND it's hamronics then you NOW have it doing 3 jobs at the rear - anti-roll, spring AND damper. I jsut dont' see that being controllabel to have a reasonably wide range of handling for differing surfaces.
For race car dampers the engineers are really concerned with shock velocities around 1"/sec. I assume the natural frequency of any suspension parts would be much higher.



erm, that might be true for something like an oval where suspension transitions are gentler. BUT there is NO WAY a suspension is designed around 1"/sec velocities for a road cricuit :)
Do you have a link as I'd like to check up on that one as I'm very surprised by it. Maybe we are talking different velocities.


3rd. It has rubber mounts at each end and I think at the points where it mounts to the chassis as well. These would tend to dampen vibrations.
Seriosuly ? it HAS to use poly or metalistic bushes at the ends.
IF it uses rubber mounts soft enough to compress then it will create inherently unstabel suspension movements as the rubber changes compression/rebound. Suspension designers try to minimise these. The are ONLY in road cars to reduce the vibration and nosie fromthe road surface. In race cars they are usually changed to rose jointed steel on steel to retain optimum control.
Can anyoen confirm ???

[johnnyperl]

In race cars they are usually changed to rose jointed steel on steel to retain optimum control.
Can anyoen confirm ???
yes..

[Matra et Alpine]

yes..
aha, so on the ROAD car what size are type are the mounting points ?
How much compliance is there ?
Does the Z06 handling pack replace this with rose-joints ?

[johnnyperl]

aha, so on the ROAD car what size are type are the mounting points ?
How much compliance is there ?
Does the Z06 handling pack replace this with rose-joints ?
dont have specific answers but i would say that on a typical car it would play a small part since the other components are so poor (sidewalls, ARB).
the setups ive seen use a 4cm(?) bushing fit inside the swingarm pivot with the mount passing through the center of the bushing.

[Matra et Alpine]

dont have specific answers but i would say that on a typical car it would play a small part since the other components are so poor (sidewalls, ARB).
the setups ive seen use a 4cm(?) bushing fit inside the swingarm pivot with the mount passing through the center of the bushing.
yeah that's typical jp.

replacing a metalistic bush with a poly one makes a HUGE difference in handling only matched by the change up to rose-jointed.

I'd NOT underestimate how much poor handling comes from movement in the bushes. A 1mm deflection under load in a corner can alter the camber/caster by up to a 5 degrees :) THAT doenst' make for a car easy to drive on the limit.

The "other" components don't have such a large effect - except the tyre itself which we're kind of stuck with anyway :) BUT the vector forces on the vette spring woudlnt affect geomotry at all so that's not the major issue. BUT it WILL affect the impact of mid corner bumps and undulations.

[culver]

Mantra, this conversation has become very interesting!
I’m sure much of what we are debaiting is like two people trying to describe the exact same thing. It’s a red car! No, it’s a sports car!


First, from what I have heard from the people I know in race car design (Formula Ford – Infinity Pro Series cars) they have never said anything about harmonic issues when they looked at Vette suspensions. On guy I know is trying to get the company that does the Vette springs to make landing gear springs for tail dragger airplanes.
Again, no one I know in the racing industry sees a problem with harmonics in the Vette’s design.
Has anyone reported this as a problem or is this assessment based on intuition. I ask simply because I’ve never heard this issue before.

OK, a couple of replies:

no, it works in an entirely differnet fashion.
An anti-roll bar is NOT restrained at the mountinf points, so when one suspension wheel moves up the bar is twistsed ADN TURNS IN THE MOUNTINGS to impart a force to the other side. Yes there is still a harmonic issue but NOW it is at wavelength harmonics of the length of the COMPLETE bar. And as it is NOT require to act as a sprign it is usually torsinoally VERY stiff and hence very HIGH natural frequency beyond the expected movements - because you are loking at the rate of change BETWEEN the wheels NOT between wheel and chassis.

The 'vette spring issue is that it's harmonics are at a much shorter wavelenght/higher rate.
The spring does not TWIST it bends, the bend is perpendicular to the mounting points, so it's not imparting directly to the other side.
As a wheel drops, the INNER section of the spring will go UP, hence imparting a downward force to the other side. So it performs TWO functions.

I understand how the conventional anti-roll bar twists instead of flexes. However, you can get torsional harmonics as well as flexing harmonics. I also agree that the natural frequency of the beam makes it unlikely to be much of an issue.
I’m not sure I understand your second point. I think you are saying that when one wheel goes up it tends to pull the other wheel up as well. If that is what you are saying, I would counter that this is intentional. As was mentioned in one of my original links, this was an intentional design trait of the C4-C6 leaf spring suspensions. This is exactly how the leaf spring can handle two jobs at once. The roll spring rate of the Vette is provided by a combination of the leaf spring and the anti-roll bar. I’m not sure why this would be considered undesirable. Certainly unconventional but hardly undesirable.

good point on it being composite, but I can't see how they can build in a DAMPING property for bend, vibration yeah, sure, but bend ?? Because IF they build it in to supres the natural frequency AND it's hamronics then you NOW have it doing 3 jobs at the rear - anti-roll, spring AND damper. I jsut dont' see that being controllabel to have a reasonably wide range of handling for differing surfaces.
Again, I’m not sure if I understand the damping property for bending. I think I’m unsure how much vibration you are talking about. If we are talking about macroscopic levels that start moving the wheels around then I will reiterate, I don’t think the problem exists in the first place. Sorry if I’m still not understanding the issue you are concerned with.

erm, that might be true for something like an oval where suspension transitions are gentler. BUT there is NO WAY a suspension is designed around 1"/sec velocities for a road cricuit
Do you have a link as I'd like to check up on that one as I'm very surprised by it. Maybe we are talking different velocities.
This one is easy, link below. The presentation in the link was put together by a 7 time SCCA national champion driver. He is a senior engineer at Firestone and also happens to be his own race engineer. While he has done some oval stuff most of his driving is on road courses (ovals may look easy but they also take a great deal of skill to squeeze out that last 0.02 seconds). Remember, I didn’t say that was the only frequency in the suspension’s motion, just that is was considered to be the most critical.
http://www.neohio-scca.org/comp_clinic/hand_out_reprints/damper%20_2003_handout%20.pdf

As for my third point, I’m not actually sure exactly what material they use as an interface between the spring and chassis. In the pictures it’s black. I assume it’s somewhat compliant. I’m not talking about the ends of the spring were it attaches to the suspension arms, I’m taking about the clamps that hold the spring to the sub-frames. Even at the wheel ends I imagine there is some sort of rubber layer in between the spring ends and the suspension arms. From the pictures it looks kind of like a, for lack of a better description, a bolt with rubber washers. Remember, the spring mounts at the wheels will always be in tension so a semi-compliant peace like a rubber washer will be under compression the whole time. This is different that say a suspension bushing that will transition from compression to tension under different loading conditions. I also do not know how much compliance we are talking about but having ridden in a Vette, I imagine it’s quite small. Again, I think the issue we are having is one of communication rather than facts. The illustration seems to show an A-arm pivot which is not what I’m referring to. I’m referring to the connection between the end of the leaf spring and the suspension arm. The Vette’s suspension arms and thus it’s suspension geometry are very carefully mounted and controlled.
Hopefully this first post will show what I’m talking about:
http://www.z06vette.com/forums/showthread.php?t=80265&page=2&pp=27
Note what appears to be a semi-compliant mount between the A-arm and the end of the spring. Since this joint is under constant tension I would expect it uses some sort of rubber bushing. This is not an A-arm pivot point. Those look rather conventional. You can also just see a bit of what ever compliant material they use to mount the spring to the chassis in the upper left of the picture.

[Matra et Alpine]

Mantra, this conversation has become very interesting!
I’m sure much of what we are debaiting is like two people trying to describe the exact same thing. It’s a red car! No, it’s a sports car!
Definately agree, we are discussin the issues about a gnat on the back of an elephant. The elephants' still in the room :)

howver, if you dont' midn I find it interesting as I've not foudn anyone with an undesrtanding of the Vette's operation to share REAL experience rather than datasheet-hype :)

is it OK to contine ? :) I'll leve out the pbits we're agreeing on :)


First, from what I have heard from the people I know in race car design (Formula Ford – Infinity Pro Series cars) they have never said anything about harmonic issues when they looked at Vette suspensions.
Thanks, is that the case on road circuits too ?

I’m not sure I understand your second point. I think you are saying that when one wheel goes up it tends to pull the other wheel up as well. If that is what you are saying, I would counter that this is intentional.
yep agreed, THAT is the benefit of the 'vettes use of a transverse leaf.

As was mentioned in one of my original links, this was an intentional design trait of the C4-C6 leaf spring suspensions. This is exactly how the leaf spring can handle two jobs at once. The roll spring rate of the Vette is provided by a combination of the leaf spring and the anti-roll bar. I’m not sure why this would be considered undesirable. Certainly unconventional but hardly undesirable.
because if you want a stiffer anti-roll bar then by definition you end up with a stiffer spring !!
Equally for softer.
usually if you ask a moving component to do more than one job it is a compromise.
it was only to cover that it HAS to do two that I raised it to see how do the race teams and seriosu road users resolve the need to have say soft spring to handle undulations but stiff anti-roll to hadle camber ?
Surely it HAS to be a compromise ? UNLESS there is some magic in the composite that I dont' grasp which makes a difference - hence why I wondered if fitting a mini-damper on the centre sectino of the spring was used.

Again, I’m not sure if I understand the damping property for bending. I think I’m unsure how much vibration you are talking about. If we are talking about macroscopic levels that start moving the wheels around then I will reiterate, I don’t think the problem exists in the first place. Sorry if I’m still not understanding the issue you are concerned with.
No I think we're OK, waht you're quesitoning is if it woudl results in sufficient MOVEMENT to make a difference. I was coming from the impact it would have on the ability of a wheel to follow road surface changes AND how it waould altar corner weights. harmonics are nasty and are usually avoided OR used to aid. I jsut can't see how that can be achieved in the transverse because of the mamny jobs it has to undertake. BUT as I said before, if there's seomthing clever in the composite I woudl love to know.

This one is easy, link below. The presentation in the link was put together by a 7 time SCCA national champion driver.
That looks to be for open wheel race cars where it is ULTRA stiff and so damping rates are often USED To keep suspension movement below a 1"/sec rate. For road/GT and my broader experience in setups for tarmac rallies you talk in havin to do a full 6-8INCHES of travel in less than 1/10 of a second for some events :) the norm woudl be more in the 4 inches in less than 1/4 second. A long way from the 1" per second, but that is about open wheelers - which means smooth tracks and reduced transitions and downforce. These alter the "opportunities" quite a lot. We've come at it from 2 different directions. I concur with what you're saying on those examples based on the info give, BUT the 1"/sec seems to be the minimum, the graphs show rates going out to 6" per second. But am not yet convinced in road cars on road events and tracks. A quick mental arithmetic -- if a car is doing 60mph and taking a corner on a rise that drops away by 1" and the tyre damper takes a second to get the tyre BACK in contact with the road then it takes 500 feet of tarmac before that tyre is providing grip again. it needs to do it within an inch to prevent the car spinning out :) a car with downforce PUSHES the car down in those circumstances. Still I woudl put that the histogram showing the 6" up and 6" down deflection is to handle those situations.
I dont' think using the mean on the chart works because the time you NEED the suspension and damping to work BEST are at the extremes.
Agree ?

As for my third point, I’m not actually sure exactly what material they use as an interface between the spring and chassis. In the pictures it’s black. I assume it’s somewhat compliant. I’m not talking about the ends of the spring were it attaches to the suspension arms, I’m taking about the clamps that hold the spring to the sub-frames. Even at the wheel ends I imagine there is some sort of rubber layer in between the spring ends and the suspension arms. From the pictures it looks kind of like a, for lack of a better description, a bolt with rubber washers. Remember, the spring mounts at the wheels will always be in tension so a semi-compliant peace like a rubber washer will be under compression the whole time.
"metalistic" bushes, yep they're standard to reduce the vibration problesm and NOT adversely affect suspension location and movement.
As I said their is a BIG difference from them to poly and the same again to direct.

This is different that say a suspension bushing that will transition from compression to tension under different loading conditions. I also do not know how much compliance we are talking about but having ridden in a Vette, I imagine it’s quite small. Again, I think the issue we are having is one of communication rather than facts. The illustration seems to show an A-arm pivot which is not what I’m referring to. I’m referring to the connection between the end of the leaf spring and the suspension arm. The Vette’s suspension arms and thus it’s suspension geometry are very carefully mounted and controlled.
yeah it was those pics tat rereaised my interest.
Last time around discussing this we couldn't get such clear pictures.
We're talking about the same joint - ie one likely to be rose jointed in competition.
BUT the debate does make me wonder if they can be 'smart' in the clamps the hold the spring to the chassis and built in maximum damping at the natural harminics of that length of leaf between them. yeah THAT could be done, not sure if it has enough leverage, but is possible. It may be that they have already resolved this for serious performance handling and have devloped a reasonable compormise that matches the chassis performance - after all making one MUCH better than the other is a waste of effort as the worst commponent is the limiting factor :)

[culver]

My turn to reply:

Thanks, is that the case on road circuits too ?

As for the professional opinions about the Vette’s suspension they are not taken in context of racing, just looking at the suspension of a road going sports car.

because if you want a stiffer anti-roll bar then by definition you end up with a stiffer spring !!
Equally for softer.
usually if you ask a moving component to do more than one job it is a compromise.
it was only to cover that it HAS to do two that I raised it to see how do the race teams and seriosu road users resolve the need to have say soft spring to handle undulations but stiff anti-roll to hadle camber ?
Surely it HAS to be a compromise ? UNLESS there is some magic in the composite that I dont' grasp which makes a difference - hence why I wondered if fitting a mini-damper on the centre sectino of the spring was used.

At some point in the C4 design program the engineers were hoping to use just the leaf spring and skip the anti-roll bar. As you have pointed out this makes it difficult to adjust roll rate independently from spring rate. My understanding is with out changing the spring, you can adjust roll rate by changing the location of the spring mounts. Of course this isn’t very practical and in the end they added an anti-roll bar to supplement the leaf spring. Basically the leaf spring provides 100% of the bump spring rate but only some portion of the roll spring rate (say 50%, I don’t know the actual numbers). I then use the roll bar to provide the rest of the anti-roll. Essentially the leaf provides a base roll rate. The anti-roll provides the additional rate and is used to tune the roll rate. But, for a given roll rate I can use a smaller, lighter anti-roll bar because the leaf spring is helping out. I’m sure this makes tuning the suspension different than with normal hardware but I’m equally certain that people have defined the differences. I many not have the knowledge but I’m sure companies like Lingenfelter Performance Engineering do know how to tune things.


That looks to be for open wheel race cars where it is ULTRA stiff and…
The link is definitely for racecars. The data would hold true for something like a Formula Ford that has very little effective down force. However, you are correct that’s a long way from road car suspension travel rates. On the other hand it’s not way out of line when people are taking a high performance street car to a road course (presumable with a reasonably smooth surface). I have never driven on a tarmac (minus in an airplane) so I’m not familiar with the types of bumps/pavement transitions you would encounter.

"metalistic" bushes, yep they're standard to reduce the vibration…
As I said, I’m just not familiar with the bushing used on the Corvettes. The images were of the new Z06 (505hp, looks to be quite a monster). I would expect that with this version of the Vette ride was back seat to control.
From what I’ve read about Vette’s since the C4 was released the leaf springs have never been a source of any handling issues. The C4 suffered because the suspension wasn’t well mounted. Like a Jag E-Type, the Vette used the drive shafts as one of the suspension links. In addition to limiting the geometry options the car now had some of it’s suspension arms mounted to the chassis and others effectively mounted to the dif housing. When they introduced the C5 they dumped all that and put a lot of effort into making sure the suspension arms were mounted to stiff chassis points. Since the C5 came out I can’t think of anything I’ve read that’s critical of the suspension. The biggest issues have always been visibility (you have that long hood); numb, though precise, electric power steering on the C6 (I can attest to that); shift feel. It would be interesting to talk to some of GM’s suspension gurus about the Vette suspension. I always love it when someone illustrates why conventional wisdom doesn’t always hold true*

*Speaking of defying conventional wisdom, years back Racecar Engineering Magazine had a great article looking at the Panoz front engines LMP cars.
http://www.bevenyoung.com.au/prdt880.htm
The Panoz car was a very unique LMP design. Rather than go with a traditional rear/mid engine LMP design, the car used a front mounted pushrod motor. Basically the guy who was paying the bills said make it this way. Until the dominating Audi’s came out, the Panoz cars were very competitive.
The article said while on the surface this car seams like a bad idea, the designers studied the rules and realized it could be competitive.

Motor: Normally the pushrod motor would be outclassed but in this case the cars use a supersonic air intake. Basically high reving peak hp, isn’t as desirable as a very broad power band. The large displacement pushrod seemed well suited to the restriction rules and the car was never lacking for power (I wish I remembered the details).

Weight distribution and Tires: The Panoz car was more nose heavy than the standard LMP cars (say 45% nose vs say 35% again I don’t know the exact numbers). Well the rules of the class limit the size of the rear wheels to something less that optimal for a rear engined car. At the same time the front tires could be larger than needed. By shifting weight forward, the Panoz car could take advantage of the extra front tire allowed by the rules. I can’t remember why they said it was ok to loose the weight from the back ties. Again, I read this article the better part of ten years ago.

Aero: This was where the car really shown. Because the air intake was in the nose of the car there was no need for the large air scoop behind the driver. This made the rear wing more effective because you didn’t have dirty air coming off the air scoop.

In all it was a fascinating look at how, given a unique set of rules and good understanding of the fundamentals, what seems like a bad idea may actually be a very good idea.
I really need to find that article again.

[Alastor]

*Speaking of defying conventional wisdom, years back Racecar Engineering Magazine had a great article looking at the Panoz front engines LMP cars...

That is an interesting story, sounds like a very good read.

[Matra et Alpine]

I many not have the knowledge but I’m sure companies like Lingenfelter Performance Engineering do know how to tune things.
You dont' see Lingfelter's out on the tracks of Europe !
AS we've already covered there are different expectations and environs that may or may NOT match the design goals fit for US customers.

The link is definitely for racecars. The data would hold true for something like a Formula Ford that has very little effective down force.
True, I also realised there is a HUGE hole in the guys rationale over the 1"/second travel rate. The histogram shows a bell curve and he's right most of the time it's in the 0-1 range. BUT thre are large at the extremeities as well. HOWVER< most of all it doesnt' have any inptu on how CRiTICAL that movemetn is. So for example on a straight it matters littel what you need and get from a suspension ( within some limits ) BUT on a corner that 6"/sec coudl be CRITICAL to the difference between cornering at 60 and coernering at 80 :)
So I've increased the pinch of salt I'm taking those figures with - mainly because they just don't jivbe with my own experiences ( and hence why Iwas trygin to seek reasons ie downforce and circuit ) I've NO experience in cars with large amounts of variabel downforce available :)

The biggest issues have always been visibility (you have that long hood); numb, though precise, electric power steering on the C6 (I can attest to that); shift feel.
Thansk for the info on the C$.
the "visibility" is the major reason the Biper has been taking a slating in the UK journos. With undualting twisty roads narrow for ordinary cars they alwasy complain about being slow because it's difficult to palce the car in the optimal position for line.

It would be interesting to talk to some of GM’s suspension gurus about the Vette suspension. I always love it when someone illustrates why conventional wisdom doesn’t always hold true*
ditto, it clearly works within some set of constraints.
I'd love to know them.
Partly because having used it in a proven design there MUST be drawbacks or everyone would re-adopt them. After all transverse leaf is where racing cars were in the 40s. I cant' see that it is only materials as you can get composite leaf springs for live axle cars - we were consider the "upgrade" for the MGB GT at one time.

*Speaking of defying conventional wisdom, years back Racecar Engineering Magazine had a great article looking at the Panoz front engines LMP cars.
http://www.bevenyoung.com.au/prdt880.htm
The Panoz car was a very unique LMP design. Rather than go with a traditional rear/mid engine LMP design, the car used a front mounted pushrod motor.
Noel Edmunds led an attempt to win the real Le Mans using an early Panoz. Bing a TV presenter, he used it for exposure AND made a TV show he coudl sell on the trials and tribulations of the effort. I'm afraid the inside view we got the engine was a DISASTER. Gettign it up to competitive power meant it overheated HUGE amounts and ultimately killed the engine during testing, qualifying and racing. Edmonds had full Panoz backing and everyone was trygin to find solutions. The bets they came up with afater trying lots of aero and radiator solutiosn was to run the engien below power and it STILL died in the race :(
I loved the Panoz as it was simple race car design and deserved to do better for NOT being sophiticated.
That was early days and the Panoz became competitive in the American Le Mans copy series, btu I dont' think the car ever did well in long races did it ?
[/quote]Basically high reving peak hp, isn’t as desirable as a very broad power band.[/quote]
Nice to see it recognised. it's the breadth of the power that matters NOT where it happens. A mathematician friend summed this up nicely when I was discussing the best way of comparing them - area under the graph. A higher powered but narrower band engine is matched by a lower powered but wider band engine with appropriate gearing IF the area under the power curves are hte same. So sensible these mathematicians :)

By shifting weight forward, the Panoz car could take advantage of the extra front tire allowed by the rules. I can’t remember why they said it was ok to loose the weight from the back ties. Again, I read this article the better part of ten years ago.
excellent input, never realised they took advantage of the corner weights that way.
With power limits and availabel rubber maybe they had reached optimal rear tyre sizes with lower weight and the extra weight up front would help turn-in more than the loss of exit grip.

In all it was a fascinating look at how, given a unique set of rules and good understanding of the fundamentals, what seems like a bad idea may actually be a very good idea.
I really need to find that article again.
I'd love to read it too :)
I'll try and find if that Edmonds TV show ever got to bittorrent :)

[labomba]

http://www.mulsannescorner.com/panozlmp1.html
http://www.mulsannescorner.com/panozlmp07.htm

Great tales of trials, tribulation, and going against the grain.

[culver]

No I wouldn’t expect to see many Lingenfelter cars in Europe given the few numbers of Vettes in Europe. Everything I know about the guy and his cars come from magazines. The short take is his cars almost always won the Car and Driver modified car shoot outs. He made a twin turbo 7L C5 Vette that did 0-60mph in something like 1.93 sec with DOT legal cheater slicks (Department of Transportation legal drag racing slicks). His car were generally reported to be very livable. The docile nature of the cars when the weren’t being flogged was what set him aside from his competitors. From what I read he was an accomplished tuner for both motors and suspension. Tragically he died in a drag racing accident a little over a year ago. It seemed his cars were easily capable of playing with RUF Porsches. Mind you all of this is based on what I’ve read.

The shock travel rate is based on research done buy a race engineer I know. The data was used buy Goodyear as well as being used for suspension tuning. Remember the person who put this presentation together is a 7 time SCCA national champion. These two really know their stuff. The data is a histogram of suspension motion speeds. By looking at the data you can get an idea what suspension travel speeds are most critical to work with. Keep in mind that none of this data was reviewed in a vacuum. This is based on lots of track time as well as computer analysis and driver feedback. If you check out Apexspeed.net you can see that the guy who put this presentation together (Dave Weitzenhof) is well respected for his driving talent and engineering knowledge, if often knocked for being an old fart.

I had a chance to drive a Corvette C6 that belongs to a friend in the Air Force. That car is actually now living in the UK. (http://corvette.co.uk , you may have to hit refresh a few times until the non-generic picture come up). The car in the link is the one I drove before it headed over the pond. Compared to the Miata I was driving the forward visibility is some what limited. Not to the point that I would refuse it but not the best. The rear visibility is also less that the best but actually somewhat better than a Miata with the top up. Compared to the Formula Vee I drove a few years back the forward visibility is great. Mind you in all cases I’m talking about seeing what is right in front of the car. If you have ever sat in anything like an F1/Indy/F3000 car understand it’s very tough to see what’s right in front of the car. Either way, if you get a chance to drive a C6 don’t pass it up. I’m not going to claim it’s the best car in the world or anything like that but it is really fun and that’s what matters to me.

I don’t know much about the Panoz LMP history. Know the original coupe wasn’t very successful. When they turned it into a prototype it did pretty well. It did win the ALMS series one year. I think it was one of those cars that could have really done something with more money and development. However, when the indomitable Audi’s came out it was completely out classed (along with every other car).

Please let me know if you find that Edmonds episode, that would be really cool to see. If you happen to know a place that has Racecar Engineering the link above was the issue in question.

[culver]

OK, I know I am pulling up a post that is almost 3 years old but... I recently added quite a bit of information to the wikipedia entry on this topic. Specifically I added a number of illustrations in an attempt to make the operation of the spring more clear. I would greatly appreciate any feedback or suggestions people might have that would make the entry even clearer or would improve people's understanding. That includes changes to the CAD illustrations.

Thanks!

Corvette leaf spring - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Corvette_leaf_spring)

[henk4]

I had not seen this thread before, and admittedly I now just glanced through, looking for one thing that I think is also worth mentioning, namely that the Corvette factory racing cars are fitted with coils springs, the reason being that these seem to be must easier to adjust. Is this correct?

Edit: Herewith a picture of the front suspension of the Z06 which was used by Markland Racing last year as a GT2 car in LMES.

[culver]

I speculate the reason the Corvette racing car uses the coils is due to ready parts availability. A racing coil spring is not vehicle specific. You specify diameter, rate, etc and you get a spring. Additionally, spring winding equipment is very flexible. So if say Hyperco doesn't have the exact spring you want they can make it relatively inexpensively and quickly.

However, the fiberglass leaf spring is application specific. As such it would be a custom fab job to make just a few springs for the car. This isn't a big deal for the production Corvette. What's 200 prototype springs when GM will make well over 100,000 of the production springs. In racing we might be talking about wanting say 10 sets of 10 different rates. Given that most racing dampers short of those used in F1 are designed for coil over applications, why not use what is readily available? In this case I really think it's a case of what works easily for the application vs what works in volume.

[henk4]

I speculate the reason the Corvette racing car uses the coils is due to ready parts availability. A racing coil spring is not vehicle specific. You specify diameter, rate, etc and you get a spring. Additionally, spring winding equipment is very flexible. So if say Hyperco doesn't have the exact spring you want they can make it relatively inexpensively and quickly.

However, the fiberglass leaf spring is application specific. As such it would be a custom fab job to make just a few springs for the car. This isn't a big deal for the production Corvette. What's 200 prototype springs when GM will make well over 100,000 of the production springs. In racing we might be talking about wanting say 10 sets of 10 different rates. Given that most racing dampers short of those used in F1 are designed for coil over applications, why not use what is readily available? In this case I really think it's a case of what works easily for the application vs what works in volume.

very plausible, is there any official statement from Pratt&Miller or Corvette Racing?

[culver]

Not that I've heard of in my nonexistent research.

I did have a talk with an aftermarket tuner who wasn't fond of the leaf spring. However, in talking to him I really took away that he had issues with the specific implementation rather than the fundamentals of the concept. He did say it was easier and more cost effective for him as a tuner to do his job using coil springs. While he didn't like some of what GM did with the leaf spring, I get the feeling he wouldn't have been any happier with the work had it been done with coils. He did state that he things GM's work is good for the majority of owners and a number of his changes had nothing to do with the springs. While he wasn’t able to improve my insight into the nuances of the leaf spring, he did at least back my view that the move from the leaf to coils has more to do with familiarity and parts availability than any fundamental flaw in using a leaf on a production car.

[henk4]

Not that I've heard of in my nonexistent research.

I did have a talk with an aftermarket tuner who wasn't fond of the leaf spring. However, in talking to him I really took away that he had issues with the specific implementation rather than the fundamentals of the concept. He did say it was easier and more cost effective for him as a tuner to do his job using coil springs. While he didn't like some of what GM did with the leaf spring, I get the feeling he wouldn't have been any happier with the work had it been done with coils. He did state that he things GM's work is good for the majority of owners and a number of his changes had nothing to do with the springs. While he wasn’t able to improve my insight into the nuances of the leaf spring, he did at least back my view that the move from the leaf to coils has more to do with familiarity and parts availability than any fundamental flaw in using a leaf on a production car.

what it apparently sort of boils down to is that in 95% (or more) of the cases the advantages of the leaf spring will offset the versability and flexibility of the coils...if you really want to go for serious racing/tuning you may need the coils.

[culver]

what it apparently sort of boils down to is that in 95% (or more) of the cases the advantages of the leaf spring will offset the versability and flexibility of the coils...if you really want to go for serious racing/tuning you may need the coils.

I would also add the availability of coil springs.

[NSXType-R]

Yeah, I glanced over this thread too.

Does the C6 also use leaf springs?

I'll read the rest later though. Interesting stuff.

Too bad most of the original links are gone.

[Kitdy]

Does the C6 also use leaf springs?

Yes it does.

[culver]

But but but...

did anyone look over the new edits to the wiki entry. I put some time in this weekend on changing/updating the illustrations in the entry. I'm hoping to get suggestions from the members on any changes which might make the illustrations clearer or easier to understand.

Corvette leaf spring - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Corvette_leaf_spring)

[baddabang]

Yes it does.

Fail. It only has one. Therefore it uses a leaf spring.

[culver]

Actually it has two. One in front and one in back. Any feed back on the illustrations?

[Matra et Alpine]

The problem with using the transverse leaf in a race car is that it is then very expensive ( near impossible ) to have different springing rates on each corner. This you do often for different tracks to get optimal speed through the most important corners.
For road, the new compsite ones certainly have some merit :)

[culver]

Matra,

If you dig through some of the recent edits you will see that one editor copied a section of one of your posts from this tread and used it as an entry (with out a cited no less!). I think the author in question was ticked that I pulled out a reference to a Motor Trend article.

[RacingManiac]

BTW if they were to use leaf on the C5-R/C6-R it'd be more difficult to swap spring....While at the same token this technology of transverse leaf might not be beneficial in a NASCAR type of world of asymmetrical car setup as a single transverse leaf spring for 2 sides guarantees symmetrical rates....


quoting my own post form 2005 to answer Henk's question...

[henk4]

quoting my own post form 2005 to answer Henk's question...

I must have overlooked it....

[culver]

From what I have heard, you can do asymmetrical rates with these springs. I have not seen how. I would speculate it involves shifting the location of the spring mounts on the chassis. That is only speculation. However, I suspect that adjustability is if nothing else, different than working with standard coils and would likely require the race engineers to work on something new for a bit with potentially little pay off.

If F1 ever moves away from the current setup where most of their "suspension" is actually in the tires, I could see them using something like these leaf springs instead of coils. With the use of torsion springs they have already shown that they are willing to develop different ideas if they see any advantage in it what so ever. If the vehicle requirements and packaging allowed it I could see them using a compact, fiberglass spring in place of a coil or torsion spring. The fact that the fiberglass spring packs more energy per mass of spring than steal would be attractive to a team. I expect the actual implementation would look different than what we see in the Corvette. Given the silly high budgets of F1 these days I could see them paying the high price if it offered some bit of an advantage.

Any feedback on the illustrations? I seriously am soliciting feedback with the intent of making changes for clarification.

[henk4]

Any feedback on the illustrations? I seriously am soliciting feedback with the intent of making changes for clarification.

If allowed, I would like to make some feedback on the Wiki text. Reference to other cars is a bit bleak, in my spec sheet the Volvo 960 always used coils, the Fiat 128 dates from 1969. Its underpinnings may have been produced a long time as a Yugo, but AFAIK this might be the last case. (I don't know what GM W-Platform stands for). On the other hand you could add the Volvo 340, which used a variomatic driven Dion rear axle, suspended by two longitudinal leaf springs.
Of course (transverse) leaf springs have been used abundantly in the past, but have now been superseded. To avoid further discussion you may want to delete the section on perception/push rod engines....(I don't think we need discussions like: The world is wrong and Corvette is right on Wiki).

[Matra et Alpine]

Culver, that F1 hasn't gone back to transverse leaf springs kind of proves the point of the benefit of coils !
Packaging is a problem for tranverse leaf, though not insurmountable.
Where would you fit the damper ? WHen you take out the damper weight a spring of modern materials isn't that heavy.

The graphics are excellent and get over how it works as a spring AND anti-roll bar very effectively. Good job :)

Also, it's correct to say that you can alter the spring rate somewhat by moving the anchor points and altering the compliance at the pivots, but that will also affect the anti-roll bar component. It woudl require a much more complex sliding-sleeve on the leaf whci then creates stress points, so no real solution.

[culver]

Well I can't guaranty all the text as I didn't write much of it. The article is Corvette specific so I think it’s OK that it only mentions others in passing. It was originally part of the Corvette entry. I’m not sure why it was decided to make it a separate entry. I do think that the Corvette’s implementation of a leaf spring is different enough from the traditional style that it deserves separate mention.

The Volvo 960 wagon used leaf springs for packaging reasons.
volvo 960 leaf spring - Google Search (http://www.google.com/search?hl=en&q=volvo+960+leaf+spring)
I really don't know much about Fiat's use of leaf springs. If I recall from, which I'm not doing well in this case, the Fiat use a metal leaf spring as both a spring and upper control arm. I have seen this on golf cars recently but I'm not sure about on road cars.
The GM W-body cars were cars for the North American market based on the "W-body" platform.
I partially agree with the point on perception. I would strongly argue that there is a perception gap. One has to look no further than the comment on the suspension when Top Gear reviewed their first C6. However, you are completely right that perception is not a technical point one way or the other. With that in mind it would be OK to pull the point.

Again, while I have edited the article in the past, as a Wiki entry no one person it 100% responsible for an article and anyone can edit it. My biggest concern is making sure people understand what I was trying to illustrate with the images. However, I'm also open to other feedback. And of course, anyone is welcome to edit the article themselves.

[culver]

Culver, that F1 hasn't gone back to transverse leaf springs kind of proves the point of the benefit of coils !
Packaging is a problem for tranverse leaf, though not insurmountable.
Where would you fit the damper ? WHen you take out the damper weight a spring of modern materials isn't that heavy.

The graphics are excellent and get over how it works as a spring AND anti-roll bar very effectively. Good job :)

Also, it's correct to say that you can alter the spring rate somewhat by moving the anchor points and altering the compliance at the pivots, but that will also affect the anti-roll bar component. It woudl require a much more complex sliding-sleeve on the leaf whci then creates stress points, so no real solution.

Has F1 moved back to coils? I thought they were still using torsion bars. Where I could see F1 using a leaf spring would be as a flexure based suspension pivot. It would have the benefit that you have no static friction in the movement (F1 cars already use flexure based joints in the suspension for this reason). It would also avoid the off axis loading issues that coils have when placed around a damper. Of course F1 teams have dealt with this in the past by using things like the Hyperco-ICP pivoting spring perches.

I do see the issue with changing anti-roll rates while changing spring rates. These are factors that aren’t an issue for a manufacture where you don’t have to spend as much time thinking about how hard is it to adjust this suspension on a weekly basis.

PS: Thanks for the feedback!

[RacingManiac]

The problem would still be in the adjustment of it, as it would necessitate changing of suspension arms or the likes when adjusting spring rate, where as you can swapout torsion bars no more difficult than coil spring....

[culver]

In the case of an F1 car I'm envisioning a spring/suspension flexure in one unit. I'm not saying I have all the details worked out, not even close. I'm only that I could see an F1 team using the technology.

[wwgkd]

To avoid further discussion you may want to delete the section on perception/push rod engines....(I don't think we need discussions like: The world is wrong and Corvette is right on Wiki).

Well, getting slightly off subject it's not only the Vette that uses them. You can make an argument for the Viper being a brute force apporach, but it now has not only pushrods, but also variable valve timing. The Saleen S7, one of my all time favorite cars, uses 2 valves per with pushrods, too.

Seriously though, cool stuff in this thread. I didn't have the money to celebrate the end of projects for the semester by drinking, but I spent the night reading this instead. It was a great alternative. If I can find it I have an old printed copy of an article I found which discussed leaf vs torsion springs in 1,000ish pound cars. It is probably 6-7 years old by now, but at the time I was doing the research there wasn't a whole lot I could find on the subject.

[Matra et Alpine]

In the case of an F1 car I'm envisioning a spring/suspension flexure in one unit. I'm not saying I have all the details worked out, not even close. I'm only that I could see an F1 team using the technology.
Watch out as likely to fall fouol of the rules :(
A team had flexing parts but they were banned as they were deemed to be "movable aerodynamic devices".
If you kept the flex out of the airstream then I reckon you might get awy with it ... BUT .... what is the advantage ? How woudl the flex alter the suspension geometry and how woudl you control flex caused by torsion and flex by compression ? Too many difficulties I think ..... hence why springs have lasted 100 years :)

[culver]

Hey,

I have been of this forum for a bit. Sorry for the delay in getting back. BTW, some new info has come up since I last added this. I’ve added a finite element model of a leaf spring mounted as GM has done to the article. It shows how lifting the right side actually causes the left side of the spring to also move up.
Image:Deformed spring model iso and plane.JPG - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Image:Deformed_spring_model_iso_and_plane.JPG)

Also, there was a person who was arguing with me regarding the Corvette leaf spring acting like a live axle. The person had cited a MT article which stated something to that effect. Via the Motor Trend forum we found out what the MT editor had meant by his comment… and it was incorrect. He was basically assuming that because the two sides of the spring were connected, pulling up on the right would make the left go down like a seesaw. Completely wrong as the illustration above shows. Even the magazines get it wrong from time to time.

Matra,
The flex part and moving airfoils could be an issue. Of course the existing suspension arms do flex. All materials under load will flex to some degree… but most of the time the flex is so small as to not matter.

The whole flex idea has all sorts of implications. Mind you grand prix cars (and many other cars) in the past did use leaf springs as both spring and arm. Flexures as suspension joints are common in racing. F1 cars have used them at suspension pivots in recent years.

Opel’s racing version of the Astra did something similar. The rules for what ever class the Astra was running in said the car had to run the same rear suspension as the production car; a twist beam. Well the problem with twistbeams is their tendency to toe out the outside tire under hard cornering loads. The engineers were only allowed to have suspension “joints” where the existing Astra had them. So the engineers made a rather complex, triangulated looking twist beam that used a number of flexures. Like a real twist beam the assembly was supposed to flex as the suspension was articulated. However, unlike the production parts, this acted like solid links with pivots at the ends rather than a continuous, flexible structure. It was written up a year or two back in Racecar Engineering magazine.

Fun stuff.

[efranzen]

Sorry for digging up this old thread, but I wanted to add a comment about coil vs leaf springs in a racing application. One other advantage of having coil-overs is the ease and range of adjusting the ride height. It is possible to adjust the ride height on C5/C6 Vettes but the range is limited and the control is not as precise. Most people who seriously track their Vette will put on something like the Pfadt adjustable coil-overs.

By the way, I really like your Wiki page on this. It's extremely informative and the illustrations really help to clarify the operation.

[cargirl1990]

Are there leaf springs on different trims on of the Corvette? I always thought that leaf springs were for the truck beds.:o

[pimento]

All road going Corvettes feature a transverse leaf spring rear suspension setup. Wikipedia knows all.

[culver]

Sorry for digging up this old thread, but I wanted to add a comment about coil vs leaf springs in a racing application. One other advantage of having coil-overs is the ease and range of adjusting the ride height. It is possible to adjust the ride height on C5/C6 Vettes but the range is limited and the control is not as precise. Most people who seriously track their Vette will put on something like the Pfadt adjustable coil-overs.

By the way, I really like your Wiki page on this. It's extremely informative and the illustrations really help to clarify the operation.

Thank you for the complement. It is appreciated!

I thought I would comment on the adjustability aspect. I think the difference as it relates to the Corvette is largely a case of OEM hardware vs aftermarket. Certainly the OEM springs are more adjustable than those on most cars which are non-adjustable. Of course the OEM systems are also generally not designed with user adjustment in mind. I suspect a leaf spring system similar to the Corvette's could easily be made to have good adjustability. For example, if the system used a pull link like the C3 rear end then height adjusting would be very easy.

When an owner wants damping and spring rates that are different than the factory rates it certainly makes sense to use coil overs. After all, custom coils are far cheaper to make in low volume than a custom leaf spring.

[cambertoes]

anyone know about the zo6's, are they any good?

[henk4]

anyone know about the zo6's, are they any good?

I have removed your link to the Corvette tuning site. May be you can rephrase your question.

[culver]

Well Mr Spam brought this page back from the dead so I figured I would add a link to this recent Edmunds article. It's got a number of great shots of the Corvette's suspension. In several of the shots you can the the very limited space between the dampers and suspension arms which encouraged GM to continue the use of the leaf springs rather than switch to cheaper coils.
2011 Chevrolet Corvette Z06: Suspension Walkaround (http://blogs.insideline.com/straightline/2010/10/2011-chevrolet-corvette-z06-suspension-walkaround.html)

[Kitdy]

We will see what the C7 has - leafs or coils.

I've heard the rumour of it being mid-engined - the same rumour that apparently starts for every Corvette generation - but at this point, I think that'd be dumb.

[culver]

From what I've read (which isn't much). The C7 will be another evolution of the basic C5 design. That's not saying the parts will be interchangeable but the basic design will be used for a third time (the Solstice and Sky almost count as a forth time given their similarities). However, I suspect just as the C6 was basically an improvement in all ways over the C5 the C7 will be an improvement over the C6. If the new chassis is basically the same design as the C6 then I suspect we will see leaves again. The story is the C7 will be a short term car and the C8 will be the next full up redesign. The C8 may lose the leaves. It does make sense to dump them if possible only because the extra cost is significant compared to the extra benefit.

As for what type of chassis the C8 should have, that's hard to say. The current layout is nice because the car is quite livable/usable as is. You have a good sized trunk and great performance. However, GM is also likely hitting the limits of what they can do with that layout. I'm sure they aren't at the limit yet but a switch to mid engine could help performance quite a bit. However, there are two issues. One is the hit to practicality. Many people like the Corvette in part because it's so livable. The other issue would be parts and costs. The Corvette needs to turn a profit despite being low volume. Right now we have a Corvette only chassis. So long as that stays true GM has to be very frugal since they can't share many Corvette parts with a higher volume line as Nissan does with the 350Z for example. The designers of the C5 had always hoped for a rear mounted gear box but they were only able to get one when the truck group decided they needed an automatic transmission that could have a bolt on bell housing and a transfer case. Those features meant the same basic transmission could be used in a rear mount setup. That saved the Corvette team millions of dollars. Basically had it not been for the high volume truck group picking up that tab the C5 would have remained with a front mounted transmission.

[Kitdy]

The other, more important, non-design/cost issue related to a mid-engined format for the Corvette is nearly 60 years of tradition.

[pimento]

A next-gen Zeta platform could be designed with the 'Vette in mind, that'd share things with the Conformadore anc Camaro and whatnot. 'Cept the rear gearbox, that wouldn't make sense in a family car.

[Matra et Alpine]

very limited space between the dampers and suspension arms which encouraged GM to continue the use of the leaf springs rather than switch to cheaper coils.
Don't see that :(
The white arrow clearly shows where they could VERY easily fit ( and always have been able to ) a decent coil over and STILL have room for the fancy adpative damper setup :)
Econoboxes put double wishbone into much smaller spaces.

[henk4]

Don't see that :(
The white arrow clearly shows where they could VERY easily fit ( and always have been able to ) a decent coil over and STILL have room for the fancy adpative damper setup :)
Econoboxes put double wishbone into much smaller spaces.

if there was that little space, why do the Corvette GT racers than go for coils?

[culver]

Don't see that :(
The white arrow clearly shows where they could VERY easily fit ( and always have been able to ) a decent coil over and STILL have room for the fancy adpative damper setup :)
Econoboxes put double wishbone into much smaller spaces.

In at least one photo the clearance between the damper shaft and A-arm in full droop appears to be less than 1/2"
http://blogs.insideline.com/straightline/2011_corvette_1600_sus_rr_oa_low.jpg

Yes, you can fit coils but they now must be either below or above the A-arms or you must limit droop as compared to the factory fitments. Here are two examples:
http://img4.imageshack.us/img4/7465/asuspension.jpg
http://www.honda.co.jp/ACCORD/webcatalog/driving/front-sus/front-sus.jpg

Note that to create clearance the designs are much taller than the Corvette setup. Note that both designs use an upper spindle pickup point which is way outside of the wheel. That ends up not being a smaller space when you are done.

A much closer design would be that of the GM Kappa platform. The Kappa chassis is closely related to the Corvette.
http://www.solsticeforum.com/photopost/direct_data/3014/medium/26Solstice_rear_suspension_2.jpg
http://www.solsticeforum.com/photopost/direct_data/3014/26Solstice_front_suspension.jpg
This design suggests it could have been done with coils. However, at this point we need think about it, GM clearly knows how to do a similar suspension with coils. Coils are cheaper. GM chose to use a much more expensive spring. So either the GM engineers, who are always accused of trying to save a buck, were dumb and chose the leaf or actually did find that they couldn't meet the packaging requirements and chose an alternative spring type hence the leaf. Note that the Kappa design, unlike the Honda design wouldn't raise the hood line much vs the Corvette setup though the Vette design keeps the top of the damper still lower than the Kappa setup.

It's possible the Kappa design, by having a wider A-arm would have clearance issues with wider wheels. It is clear that when doing a Corvette like suspension with coils GM felt they needed far more clearance around the damper than the Corvette offers.

[culver]

if there was that little space, why do the Corvette GT racers than go for coils?

There are several practical reasons. First, they don't have to worry about coils lasting 200,000 miles. This means they can use coils that are operated closer to their elastic yield limit and not worry about cyclic fatigue. Second they can limit the total travel of the suspension so they stay in the travel range of the coils. This allows them to use smaller, stiffer coils. So that is what makes their application different than an OEM application and thus makes it possible for them to use coils when GM Engineering said coils won't due in this application.

Now as to why they would want to switch, well as I said when I started this thread a long time ago, racing coils are a universal item. Just specify a few basic parameters and the same coils which are used on a racing Ferrari could be fitted to a Corvette or a Nissan Z car. This means you have a very wide range of coil choices. The leaf is specific to the Corvette only. So it would be expensive to stock a large range of leaf spring rates. It's simply cheaper and more practical to accept the limitations of coils (which don't really mater to the racing teams) to gain low cost and wide selection (which does mater).

[culver]

A next-gen Zeta platform could be designed with the 'Vette in mind, that'd share things with the Conformadore anc Camaro and whatnot. 'Cept the rear gearbox, that wouldn't make sense in a family car.

I suspect we could see just that. At least I would expect to see more parts sharing. Of course it will depend in the end. I think the current GM RWD chassis use rather tall suspension bits. Part of that makes the Corvette different than other GM RWD platforms is the very low fender lines.

[RacingManiac]

There are several practical reasons. First, they don't have to worry about coils lasting 200,000 miles. This means they can use coils that are operated closer to their elastic yield limit and not worry about cyclic fatigue. Second they can limit the total travel of the suspension so they stay in the travel range of the coils. This allows them to use smaller, stiffer coils. So that is what makes their application different than an OEM application and thus makes it possible for them to use coils when GM Engineering said coils won't due in this application.

Now as to why they would want to switch, well as I said when I started this thread a long time ago, racing coils are a universal item. Just specify a few basic parameters and the same coils which are used on a racing Ferrari could be fitted to a Corvette or a Nissan Z car. This means you have a very wide range of coil choices. The leaf is specific to the Corvette only. So it would be expensive to stock a large range of leaf spring rates. It's simply cheaper and more practical to accept the limitations of coils (which don't really mater to the racing teams) to gain low cost and wide selection (which does mater).


Not to mention its easier to change/adjust coils for setup reason....

[culver]

Actually in the case of the Corvette the leaf is easier to change and possibly even to adjust but it's not conventional. The Corvette leaf can be replaced without unbolting the shocks.

[RacingManiac]

But you have to change a pair of them at the same time. Its not unusual to run asymmetrical setup even for road courses....

[culver]

Actually you can get asymmetrical setups with the leaf spring but it's not as intuitive as doing the same with individual coils. As a point of interest, when Pratt and Miller did their C6RS road car they retained the leaf springs (though not the factory springs IIRC) rather than change them out for coils as they used on their C6-GT cars.
Pratt & Miller C6RS (http://prattmillerc6rs.com/features.htm)

Also interesting that they changed the seats to ones appropriate for a car of the Corvette's capabilities... man GM needed to do that a long time ago!

[fpv_gtho]

A next-gen Zeta platform could be designed with the 'Vette in mind, that'd share things with the Conformadore anc Camaro and whatnot. 'Cept the rear gearbox, that wouldn't make sense in a family car.

Rear transaxle might actually work pretty well, and will undoubtedly happen in the future. Dont think theres a chance in hell Commodore and Corvette will share any more than engines though. Maybe electrics and some other systems, but nothing structural.

[RacingManiac]

Yeah I know C6RS, the company I work for did the height adjustable airspring on the car. Also saw one couple weeks ago at Novi MI....

How do you do asymmetric rate on one leaf spring? I can see you can do preload, but rate can't be different on the same piece of leaf?

[culver]

I'm not sure how it's done but Vette Brakes and Products says they can do it. My GUESS is they move the leaf spring pickups either on the A-arm or at the chassis. You could also make an asymmetric leaf. Let me reiterate that these are guesses.
Corvette and the leaf spring... (http://www.corvetteactioncenter.com/forums/c6-general-discussion/64802-corvette-leaf-spring.html#post597274)

[Matra et Alpine]

culver, the first pics of suspension you show are so old it is laughable :(
The latter set you're getting close to modern setups used in US cars perhaps.
BUT, modern cars are using much more complex and compact than any of those.
AND that I think is the poitn, it is more expensive.
So we get an excellent handling econobox for the price US consumers are used to paying for "top of range" Fords and GMs.
Different customer-focus.
and when you get to "performance" cars then many are already supplied with or offer remote reservoir coil overs thus reducing the space needed and most importantnly of all providing cooling on the harder working short throw.

[culver]

Matra,

I don't think you intended it this way but your US vs Euro comments can be taken to be quite condescending. Let's please not let this devolve into an us vs them sort of discussion.

The second picture I included is the 2010 world version of the Honda Accord. That is hardly an outdated design. It looks very similar to the current front suspension used on the Fiat 159. It doesn't seem any more compact than the system Honda is using.
Agility with total control - Alfa Romeo Hong Kong (http://www.alfaromeo.com.hk/innovation/handling/alfa-159-brera/)
I don't see anything suggesting that the design used by either make is outdated.

Which econoboxes are still using double wishbones in front. In the US market Honda was the last to move over to struts. I know we don't get the range of small car's Europe gets but really, how many are using double a-arms in front?

Incidentally when Honda did the S2000 they put the spring above the upper A-arm.
http://automobiles.honda.com/images/2006/s2000/engineering-photos/double_wishbone_suspension.jpg

Now the Corvette setup doesn't look radically different than this picture
http://site.titanmotorsports.com/blog/wp-content/gallery/novitec2/NovitecF430-19.jpg
The Ferrari does mount the damper higher up (thus making for a taller overall assembly than the Corvette. The Ferrari also clearly bows the upper A-arm to clear the springs. Ironically the Kappa pictures seem to have a suspension setup (not the chassis structure but the damper, arms, spring etc) that looks very similar to the Ferrari setup. The biggest differences I see are the Ferrari mounts the outboard joints in double shear and the upper pickup for the damper is strut like in the Kappa (and more like mass market double wishbone setups).

Comments about remote reservoirs are a red herring. How many sports cars that cost about the same as the Boxster come with remote reservoir dampers? Of course Ferrari is using a set of trick magnetically adjusted dampers in the 458. They look a lot like the ones in that Edmunds link...

I can't say why GM didn't bow the upper A-arm to fit a conventional coil but I can't see any reason to dispute their packaging claim. No other explanation passes the sniff test.

[RacingManiac]

Don't a lot of "modern" econoboxes in Europe still uses twist beam setup at the back anyway? Doesn't seem to diminishes their handling necessarily, just like some IRS rear setup can also drive poorly. We have a couple of Peugeot at work that we work on here(407s) and while they are neatly packaged and compact(great trunk space), the motion ratio for the spring and damper is poor and a lot of that is driven not by "performance" but rather packaging. The stock vehicle also doesn't drive very well, but Peugeot now probably rates pretty low on the totem pole anyway. Complexity is not necessarily the answer to the optimum handling car, rather I see most of the time to address packaging issue. Most multi-link setup now are designed to be geometric/mechanically overconstaining, but through bushing and compliance tuning to allow them to be kinematically "solvable", thats something you won't see in a performance oriented car(say, a open wheel car or a Caterham, for example).

[Matra et Alpine]

culver, it is a matter of FACT that us consumers have cheaper cars and that the designers aim to meet that expectation.
THUS why most of Ford range is 2 year old designds from RoW until recently :)

in terms of age of design, the pics you showed are OLD>
That it is on a new car is irrelevant.
Look at Mini and the original Z rear for examples of innovative and different to get packaging right.

EVO and Subaru performance versions come with remotes ( or they do here )

Other explanatinos to "pass the sniff test" are they jsut want it to be that way.
It is "tradition" and no amount of defending it works :)
It's like the original air-cooled REAR engined 911s. EVERYONE new there was a better way but 911 buyers didn't want change and so Porsche had major develompent programs to make it work !! Motor industry is FULL of examples, just I suspect WE are nto as touchy or have as big a chip on shoulder about it :)

[Matra et Alpine]

RM, yes torsion bar suspension was always a common system in France to handle the very rough roads they were used to and modern systems used them for packaging.
A good torsion bar is the equal of a spring !
Competition and adjustability.
My Matra has torsion front :) Best of all they are VERY easy to swap in/out and heat treating can adjust characterstics ! To be fair I've only 2 sets for the Matra as I've avoided too stiff.

BUT the development of advanced shocks has led to a massive reduction in size and so the space is readily found for coilovers for performance cars.

Ps, THe torsion in MODERN cars is about the rear passenger width, not the boot (trunk) and so as cars have become MORE compact and still want 4 seats then more have and will go that route. Trailling arm and torsion bar and with the likes of the BMW Z-links provide good performance. And in FWD competition cars there is buggar all weight at the back to control anyway :)

[culver]

I'm not disputing that. I agree that on the whole US consumers are more cost contious and less interested in paying extra for features in our cars. However, this isn't just a Big 3 thing. Honda, Toyota, Nissan, Hyundai and VW all see this hence they produce cars that target American taste. This is traditionally, softer riding, larger cars with larger displacement motors. GM and Ford knew this first but the others figured out it wasn't backwards engineering but customer preference that dictated those features (that isn't saying the Big 3 didn't have their owner backward issues).

You are claiming the Honda design is old, well prove it. That car is only what 3 years old. What makes that an old design. Can you show a modern version?

The Mini was innovative... decades ago. However, we shouldn't try to play that game. The Corvette's 1963 suspension was very innovative compared to most IRS designs in 1963. It was one of the earliest multi-link road car designs.

As I recall you guys in the UK get very high performance versions of the EVO and Subi. I also believe those start to really take a hit in terms of daily driver status. The Corvette is more in line with the 911 in terms of comfort while still having performance.

The claim that it's tradition is just flat wrong. Do you really think GM decided it was better to spend the money developing a new pair of leaf springs for the C5 rather than using a set of coil springs? Come on. When the C5 came out no one even realized or ever complained about the leaf spring. It had no tradition or history. Almost no one knew or cared until the C5 was getting long in the tooth. The C4 reviews hardly mention the spring design. All Corvette's Are Read mentions the discussions regarding the car's suspension design. The engineers never set out to use the leaf design because they knew it was expensive and from a marketing POV offers no value to the customer. We have a company with a reputation for going too far to cut costs and now you are claiming they chose an expensive option because they just thought it was cool? This isn't like a front engine Porsche where people rejected the 928 as a 911 replacement in part because it wasn't a flat 6 under the tail. No, the Corvette DID use coils for many years. The classic Corvette have coil springs. The leaf was a purely engineering choice because NO ONE would have missed it had GM selected coils in 1997 (or 1995 or when ever the real choice was made).

No, claiming GM did it because doesn't pass the sniff test.

[culver]

Don't a lot of "modern" econoboxes in Europe still uses twist beam setup at the back anyway? Doesn't seem to diminishes their handling necessarily, just like some IRS rear setup can also drive poorly. We have a couple of Peugeot at work that we work on here(407s) and while they are neatly packaged and compact(great trunk space), the motion ratio for the spring and damper is poor and a lot of that is driven not by "performance" but rather packaging. The stock vehicle also doesn't drive very well, but Peugeot now probably rates pretty low on the totem pole anyway. Complexity is not necessarily the answer to the optimum handling car, rather I see most of the time to address packaging issue. Most multi-link setup now are designed to be geometric/mechanically overconstaining, but through bushing and compliance tuning to allow them to be kinematically "solvable", thats something you won't see in a performance oriented car(say, a open wheel car or a Caterham, for example).

Twist beams can actually work quite nicely. A lot of people get bent out of shape because they aren't "independent" but they can actually be very cleaver in their "non-independence".
This wiki entry shows how a twist beam can keep the wheels parallel bounce but allow camber gain in roll. Very clever. I think Audi was the first to figure this out.

[RacingManiac]

Funny about that reduction in size for "advanced" shock, I got a Sachs unit sitting on my desk now from one of the new Bimmer(I think its the 2011 X6 or the 7 series), its got 2 solenoid valves one for each direction and a controller tack on to the side of it(whole thing is $800 a pop from the dealer, may not sound like a lot compare to a machined racing damper, but typical road car shocks are dirt cheap), this thing is massive....

Shock sizes are not necessarily just they are "advanced" or not. The force requirement and how they are packaged drives greatly on how big they are, and then the whole strut vs damper only is another issue too. Poor motion ratio means you need more damping force to be effective and if you are limited in travel then you need even more. And that drives for larger piston and rod size. If you are using a damper as a strut(which I believe WRX does), you are required to have a bigger rod diameter because it needs to take significant side load, and that means you need to have a bigger fluid reservoir to take up the rod flow, and AFAIK Subaru still runs their inverted strut? That means conventional twin-tube valving won't work(they don't work upside down), so a remote design is needed to run a gas charge with a separating piston in them.

Passenger car stuff is so packaging driven that there are no set formula on how to make something.....majority of how well the final product drives ends up I believe not necessarily due to what type of layout they choose, but who's calibrated butt they are using for that ride/handling engineer and how much time they spent on it. In NA the requirement typically is so different from Europeans that the cars ends up driving a certain way.

[Matra et Alpine]

jeez guys I do wish you'd do soem critical thinking before posting @(
REALLY reading the responses shows NO attempt to understand orirginal points.
First Honda suspension. Go look at Rover designs in the 60s.
Next MINI Z-beam is BMW Mini.
Next Evos etc are used daily and we've got shitty roads. ALREADY SAID, cultural/customer preferences. But I'm using it to point out solutions ARE there. Nobody seems to graps that not so hidden message !
"tradition ... flat wrong" -- BS I claim, jsut look at the COrvette fans who demand the "same" ... yes another possible mid-engine idea put fgorward which will get thrown out as "not a corvette". Look at all other cars who have better handling, built to price and more flexibility ?
"sniff test" -- roflmao - don't know what you're sniffing :)
911 - again PLEASE think before closing the mind :( air-cool rear engined IS the 911 and IS - AS I SAID - difficult for Porsche to have developed to the handling levels it has. TRYING to pick the direct opposite 928 etc is just pointless and missing ANY chance to engage in any sensible discussion on the subject :(
SACHS units for Seris 7 or X6 -- you SERIOUS ? Totally different beasts and weight !
Really this is pointless. Hey look, I've got a coil over from a ceterham R500 so I've "proff" it coudl be tiny. Get real. OF COURSE it would be too small and not up to the task. Please don't muddy reasoning with arguing. This is like wathcing GLenn Beck on automotive design :)
"cars end up driving a certain way" and thus WHY Corvette owners will want ti ever to stick leaf ? Or are you pickign a different tack.
I'm out of this - again - as the discussion is going nowhere for as long as you guys are going to take extremes when a minor step is being pointed. That's just plain poor detaing and woudl lose in every step.
Bye.
See you in 2 years when Corvette come back to debating the leaf/spring choices and nothing will have changed.

[culver]

Matra, I don't think your last post really made any sense. I think you are saying since the Honda design isn't brand new it's thus out of date? I mean pneumatic tires have been around for a long time so the latest and greatest Michelines aren't late or great? You said the Honda design isn't up to date, prove it. Tell me what about Honda's design makes it old fashion compared to what IS the latest and greatest in double A-arm designs on family cars. What should Honda have done to make this design up to date? What is state of the art according to you?

Evos are used as daily drivers here as well. However we don't have the models with well over 300hp. Regardless, I can't think of many cars that come with remote reservoir dampers. A few special cases does not prove your point. Ferrari seems to think the Corvette dampers are really trick as they are using the same system on the F458


tradition ... flat wrong" -- BS I claim, jsut look at the COrvette fans who demand the "same" ... yes another possible mid-engine idea put fgorward which will get thrown out as "not a corvette". Look at all other cars who have better handling, built to price and more flexibility ?
"sniff test" -- roflmao - don't know what you're sniffing

Corvette owners and fans don't speak with one voice and don't all demand the same thing. Some want to keep V8s, some don't. Some want front engine, others don't. However, some parts are rather part of what people see as traditional Corvette. The front engine RWD seems to have settled in as part of the Corvette's legacy the same way the 911 is supposed to have an H6 behind the rear axle. The leaf spring is not part of the Corvette legacy any more than the targa top or the front coil springs (used on all Corvettes through 1982. The leaf springs were simply an engineering choice, not a design statement. The fact that they are an expensive engineering choice means that somewhere, someone thought they were the right answer to a problem. There was no cry to retain the leaf springs when GM went from the C4 to the C5. There was a cry to retain a V8 and not move to a turbo 6 or some other motor. There was a push to stay front engine-RWD to retain the car's cargo area and the traditional long nose, short deck look of the car. There was NO push to retain the leaf springs. Again, it is dumb to think GM chose an expensive solution to a problem if a cheap option was available. You are normally a smart person so I can't figure out why you are so blind to this point.

Matra, I'm sorry but you really haven't made any sense in your last few posts. Perhaps that was your intent and I simply missed it. I think the burden is on you to make your point clear, not on us to try to decode what you think is modern or not modern.

[Matra et Alpine]

TH post rasied the points where the original post was not read and it not making sense proves it.
NO, it is NOT my "burden" to explain for example that AS I STATED CLEARLY the Honda "new" is actually an "old".
"engineering choice" -- and YET comparable cars and better/worse then package suspension using alternatives and Corvette "hang on to it" even when performance versions switch it out. Yeah, sure :(
"a few special cases" .. erm so I only listed two, you REALLY need more when the one you are citing is a case of ONE ( the 'vette ) ? Missed the point completely and I determine deliberately.
So on that I leave.

[culver]

You said the pictures I showed were old. They are of the current car so they can't be more than a few years old. Next you said the design was old and implied it was not a modern interpretation of the design.

Your comments about the Corvette read as if you are drunk. Normally you are rather clear when making a point. This time you still aren't.

Matra, really, your last two posts make me think you are drunk posting. You aren't putting together complete arguments and what ever point you were trying to make has been lost in a sea of grammatical errors and apparently random statements.

[RacingManiac]

"BUT the development of advanced shocks has led to a massive reduction in size and so the space is readily found for coilovers for performance cars."

That is all I was trying to add something to, size. I work with shocks, I see a ton of stuff coming in and out of my work and their sizes vary greatly. Nothing suggests to me that "modern" one is more or less compact because its newer or older. Corvette damper is TINY compare to something off a 911. But are they that different in how modern they are? You size your shock size base on damping need and mechanical load cases. When you got a Caterham with nice motion ratio, short travel, and less load needed, you can build a small damper. That kind of condition may or may not be available in all cases, and damper is definitely not the first thing you design and pick when one is designing any car, let alone a packaging conscious passenger vehicle.

Yes sticking to tradition for the sake of it sucks, but sales and marketing drive that anyway(blame the customer? lol). Although I am not sure if that is necessarily the case in Corvette's design. One thing that is somewhat unique still in Corvette is that its still a body on frame car(another tradition maybe?), and most of the structural packaging is still in the frame rails. The leaf spring applies their load to the pivot and thats supported across the frame, and they can potentially(not to say they did, its my guess) have a much less reinforced damper mount that only takes damping load that cantilevers off the top of the rail in its own mount. The race car is built much different structurally since much of the frame was replaced/reinforced with cages and tube frame, they can get much better load path compare to the stock chassis without worrying about the same packaging requirement. Merit of sticking with body on frame instead of unibody? That I have no idea, though it does allow them to make all their models(hard top, convertible...etc) and not sacrificing structural rigidity with or without roof... Again, my best guess....

[culver]

Actually the Corvette isn't body on frame. Body on frame is meant to indicate you have a more or less complete passenger compartment dropped onto a rolling chassis.
http://www.imperialclub.com/Yr/1966/SpottersGuide/body-above-frame.jpg
That is typical of trucks. The Corvette is more like a Ferrari or Lotus in that the body panels are attached to a frame and the interior is attached to a frame.
Lotus: http://www.lotusespritworld.com/images/Lotusmodels/lotus_elise_chassie.jpg
Ferrari F360: http://www.ferraricars.org/img/ferrari-360-modena/structure-02.jpg
C6 Targa:http://www.seriouswheels.com/pics-2005/2005-Chevrolet-Corvette-C6-structure-chassis-1280x960.jpg
Note that the central tunnel is a key part of the Corvette's structure and to this end is closed on the bottom.

The C3 was the last truly body on frame Corvette.

The racing Corvette's use the same basic chassis but add a cage and some other parts. Do keep in mind that the Corvette chassis is rather stiff. The base C6, which as a targa does not have a structural roof, is about as stiff as a Ferrari F360 (which has a roof). The Z06 and ZR1 are stiffer thanks to the inclusion of a structural roof.

[RacingManiac]

Not unitized body though, thats what I am saying. The "typical" car unitbody will have a front shock mounting point, inside a structural wheel well. In Corvette's case that would endup taking up the space by the engine, which might not have the room for that reinforcement:

Road car: C6 under the hood image by vettnutt on Photobucket (http://media.photobucket.com/image/C6%20under%20the%20hood/vettnutt/P3190003.jpg)

Race car:
http://lotpro.com/blogphotos/General%20Motors/Motorsports/tn_M10%20C6.R%201.jpg

Note the 2 truss structure that comes out from the passenger cell to the shock pickup on the race car, on the road car a bunch of auxillary stuff is packaged there. For a car typically with unitize body, the structural reinforcement there would be substantial for a spring/damper unit mounting...(DB9, I believe)

http://www.cyberweld.co.uk/pictures/cyberglue/chassis_.jpg

For Corvette the use of the transverse leaf loaded to the frame rail simplifies a lot of the design, and you are utilizing whats already there, instead of building more structure to support it...

[culver]

OK, yes I completely agree that the Corvette isn't a unibody. GM, just as Ferrari and Lotus, had to deal with the question of how to make a chassis with by automotive standards low tooling costs. The traditional dies used to make unibody cars are VERY expensive (as I'm sure you are aware). This is why the Corvette (and Lotus and Ferrari) has used fiberglass then later sheet molded composites to make the body. The low pressure tooling is far cheaper than the tooling needed to make a traditional stamped body part. It will be interesting to see if the hydroformed body panels used on the Solstice find their way onto the next Corvette. That process uses only a single sided die (vs two for a stamping) and the dies don't have to be as hard as with stamping. Anyway, the body panels on a space frame construction is common in lower volume cars because the tooling costs are lower.

You are also right about the extra triangulation in the racing Corvettes. It's understandable that any time you take a street car and turn it into a race car adding some extra bracing is basically a must even if the base chassis is well designed. Ironically I was going to include that exact same race car chassis picture!