Tyre widths in relation to handling

[fpv_gtho]

This is one of a couple of discussions that gets brought up with me, my twin brother and one of my friends. My friend claims that a car with very thin front wheels, like rims about 4 inch wide with rear wheels that are complete monsters, will give perfect (to him at least) handling. Whilst i can see some benefits in that, i dont agree, and i personally think that, say for a RWD car its fine to have fatter rears than fronts, but you want to have fronts that are at least 225's or 245's. Does anyone have any facts or opinions to support either opinion stated?

[Matra et Alpine]

This is one of a couple of discussions that gets brought up with me, my twin brother and one of my friends. My friend claims that a car with very thin front wheels, like rims about 4 inch wide with rear wheels that are complete monsters, will give perfect (to him at least) handling. Whilst i can see some benefits in that, i dont agree, and i personally think that, say for a RWD car its fine to have fatter rears than fronts, but you want to have fronts that are at least 225's or 245's. Does anyone have any facts or opinions to support either opinion stated?

Too little tyre on the fornt and you will NEVER get the car to turn in. Especially if VERY fat tyres on the rear.
Fat tyres always want to go straight, any turning of the car needs the tyre to scrub part of it's footprint as it can't all go in an arc.
So the rear fat tyres are trying to make a car go straight.
So you need to put enough grip ( and weight ) on the front to get enough grip to be able ot counteract this understeering force.
Them's the facts

I think he's confusing dragsters, they don't need the front wheels so they tend to be bicycle rims Hot rodders copy this and hence you'll see them on the streeet sometimes too.
But notice you'll never see it on track

[fpv_gtho]

thanks for that Matra. i always considered the small up front, big up back approach as better at slower speeds as there would be less resistance in the steering wheel, but the moment you started pushing the car through the corners, as you said, the rear tyres would simply be pushing the car too forward if theres not enough surface grip on the fronts.

[byronleehk]

Too little tyre on the fornt and you will NEVER get the car to turn in. Especially if VERY fat tyres on the rear.
Fat tyres always want to go straight, any turning of the car needs the tyre to scrub part of it's footprint as it can't all go in an arc.
So the rear fat tyres are trying to make a car go straight.
So you need to put enough grip ( and weight ) on the front to get enough grip to be able ot counteract this understeering force.
Them's the facts

I think he's confusing dragsters, they don't need the front wheels so they tend to be bicycle rims Hot rodders copy this and hence you'll see them on the streeet sometimes too.
But notice you'll never see it on track

Matra is right.

The front tyres are there for turning and also grip. For drag racing (i.e. straight line racing) the front's are there just to keep the front end of the car off the ground, no turning needed.

But for other forms of racing, it's there for turning and sometimes...as the Japanese have it...drifting. When you attack a turn, you are trying to shift the weight (or momentum) from the back to the front of the car while trying to cope with the cornering forces. There are often times you'll see FWD cars turn-in so hard that one of their rears is off the ground...that's the limit because a little more and the next thing you know you'll be in the gravels / run-off areas.

Correct me if I'm worng Matra

[NAZCA C2]

If you have skinny front tires you will have a bunch of understeer (car does'nt turn) but you don't want huge front tires because it will cause a lot of drag and drag slows your car. Really wide front tires would also probably slow the cars steering and could rub the fenders. On most road cars increasing the front tire width would be beneficial in two ways, it would give the car better braking and handling.

[Matra et Alpine]

If you have skinny front tires you will have a bunch of understeer (car does'nt turn) but you don't want huge front tires because it will cause a lot of drag and drag slows your car. Really wide front tires would also probably slow the cars steering and could rub the fenders. On most road cars increasing the front tire width would be beneficial in two ways, it would give the car better braking and handling.

Like evrything in the design of a car, there is a balance.

over-tyre the front and you will get excessive oversteer and the back will break away. An optimum selection is preferred to give a progressive break away on all 4 tyres and give the control over under/over steer in the drivers hands.

[Falcon500]

And not to mention that most wide tyres on any unassisted stearing makes parking more dufficult my fathers studebaker with the 14" x 7" alloy roh mags on it makes it more difficult to park...then theres drums all round and the naturally heavy stearing but that all part of the fun isnt it but that said its only slightly easier with the 14x5 steelies on it...

[Wouter Melissen]

It also depends on the wheels you have. My Mini has wheels that were designed to hold 145 tires, but 165 tires fit perfectly well. However handling is better on the skinnier tires, because of the extra roll of the fatter tires. When I need new tires I doubt I'll go for the skinnier tires though, these look really good!

[Falcon500]

Well now that you mention it wouter my old mand roh set of mags has some ungodly sized firestone rubber....much bigger then the rim itself they look great but rub on the rear guards when you give the suspension a work out Have i actually posted a good pic of my fathers studebaker (red one) in here? i know ive posted a pic of the unfinished motor and you could see a glimpse of it in the pics of my falcon...

[fpv_gtho]

It also depends on the wheels you have. My Mini has wheels that were designed to hold 145 tires, but 165 tires fit perfectly well. However handling is better on the skinnier tires, because of the extra roll of the fatter tires. When I need new tires I doubt I'll go for the skinnier tires though, these look really good!

well that can probably fall under the balance Matra was talking about, slightly. no doubt with suitable wheels, those 165 tyres would perform better.

Falc, i think my dad's got a similar setup on the Impala, the tyres themselves are 265's and the rims i think would have to be 16x7 (possibly 7.5 or 8) Cragar chrome wheels, and they have a fair bit of bubble in the sidewalls but they look the part for sure

[Ru$$ky]

Balance is the key! Front too skinny = lots of understeer, not enough grip at the front to turn-in, skinny rears=oversteer, not enough grip at the back, lots of fun or dangerous depending on the driver's skill.
Most cars have same tyres back and front.
Powerful RWD cars have wider tyres at the back to help traction.

[SilverArrowZ]

Balance is the key! Front too skinny = lots of understeer, not enough grip at the front to turn-in, skinny rears=oversteer, not enough grip at the back, lots of fun or dangerous depending on the driver's skill.
Most cars have same tyres back and front.
Powerful RWD cars have wider tyres at the back to help traction.

Very true. But try the front TOOOOO skinny (like drag setup) on drifting, you won't over steer.. no need to worry.. as you probably break the suspension first . My car is an FR and with 195 at the front and 215 at the back, it handles pretty nice, i can corner faster now

[fpv_gtho]

well on the local RWD cars here, the one with the biggest difference in treads f/r that i know of would be the DJR HP320, which has 285 rears with 245 fronts, everything FPV and HSV offer has 245's allround but i dont know what CSV put on their cars,

[V8turbo4me]

Seems to me that if you could, as if you had the room, the steering equipment to handle it, and enought power you would want to put wide tires all around to get the most traction possible. I know someone who has a corvette that has 10.5 inch wide rims all around and it handles like it is on rails. Yes the back tires are a little bigger I think like 335/35/17 and the fronts are 245/40/17 or something of this sort but the car is amazing. So I mean if your car can handle it and it wont really hurt performance isn't bigger better in this case?

[Matra et Alpine]

Seems to me that if you could, as if you had the room, the steering equipment to handle it, and enought power you would want to put wide tires all around to get the most traction possible. I know someone who has a corvette that has 10.5 inch wide rims all around and it handles like it is on rails. Yes the back tires are a little bigger I think like 335/35/17 and the fronts are 245/40/17 or something of this sort but the car is amazing. So I mean if your car can handle it and it wont really hurt performance isn't bigger better in this case?

There are dependancies.
One is weather !! In scotland it rains too often to seriously consider puttin too wide a tyre on the fronts. Rear aquaplaing is controllable to an extenet. Lose the fronts in a big aquaplane and you'll swap ends at VERY high speed. ( It rains a LOT at local Knockhill track. Swapping ends I'm used to )
Not a big issue in Ca !!
At the limit, the DRIVEN wheels should have slightly more rubber available to them than the non-driven. That ensures that in a drift you can use the power more easily.
Weight bias ( and in racing corner-weight ) is also key in determining tyre size.
It's possible to induce bad stability with them in opposition to each other - ie too little tyre on the lightly loaded corners can cause sever under/oversteer as power is applied and the weight transfer begins and changes the dynamic corner weight. In some events THAT is a good thing and actively designed - eg autotests.
Finally the scrub on the tyre due to the differeing inner and outer distances traveled on a wide wheel CAN cause less direct steering thatn the optimal size.
And in all of it, bigger tyres mean more rolling resistance. This is not a big issue with big cars with lots of power, but at the other design spectrum where light weight is sought, then rolling resistance does come into it.
In my experience in trying track configurations, my Bagheera limits the fronts at about 205s. I run 195s. On the Alpine, it sits on 225s front at the moment and I'm going to try a new wheel/tyre combo next time and go up a notch as the rear ( 265s ) are 'pushing' the front on turn-in.
Front engined, RWD has less 'weght transfer' on braking/turn-in so the 'vette is likely less critical.
With THAT amount of rubber on then in dry it should grip extremely well