Backyard Aerodynamics

[Pitwork]

I've been having a debate with a friend recently about "aero kits" or "body kits" and bolt on spoilers. This is the argument: He says that adding a proper aero kit or wing from a reputable company, such as C-West or APR will lower lap times due to an increase in downforce on the car. I contend that adding these devices is pointless becasue the car was wind tunnel tested during its design and shaped to be stable at speed. Without a way to test the effects of the aerodynamic devices, you could be screwing with the aerodynamic balance of the car and even possibly produce lift instead of downforce.

Your thoughts?

[acfsambo]

But if the companies manufactred these boydykits specifically for that car, theu could have engineered it to give the car more downforce.

[The_Canuck]

I say most of them are purely cosmetic. Unless you got one custom made for your car they'll probably only make it slower.

[Jack_Bauer]

I've been having a debate with a friend recently about "aero kits" or "body kits" and bolt on spoilers. This is the argument: He says that adding a proper aero kit or wing from a reputable company, such as C-West or APR will lower lap times due to an increase in downforce on the car. I contend that adding these devices is pointless becasue the car was wind tunnel tested during its design and shaped to be stable at speed. Without a way to test the effects of the aerodynamic devices, you could be screwing with the aerodynamic balance of the car and even possibly produce lift instead of downforce.

Your thoughts?

In terms of lap times I'd be less worried about the aero balance and more worried about the extra weight and drag of an after market body kit. I'm sure any benefit in downforce will be more than offset by these adverse effects. Kits like that are generally for cosmetic effect.

[Pitwork]

In terms of lap times I'd be less worried about the aero balance and more worried about the extra weight and drag of an after market body kit. I'm sure any benefit in downforce will be more than offset by these adverse effects. Kits like that are generally for cosmetic effect.

I agree. And I love your sig

[kingofthering]

This really depends. If you're driving something with crap-loads of extra power, then yes, it might help, but if you have something like a 300hp Civic, it probably won't work.

[coolieman1220]

aerodynamics is like a percentage it's more at higher amounts. the faster you go, the more lift you generate and the more downforce you generate. a percent is less with less amount, more with more amount. those kits probably don't help much, mostly add weight and mess up your suspension. if you put it on in ure backyard, it won't help at all. body kits never fit together right and always require body molding and body work. if you do that stuff then maybe. if you wanna increase ur handling, buy a set of high performance tires! that'll work better. besides how often do you take hard corners?

[Zytek_Fan]

In terms of lap times I'd be less worried about the aero balance and more worried about the extra weight and drag of an after market body kit. I'm sure any benefit in downforce will be more than offset by these adverse effects. Kits like that are generally for cosmetic effect.

Indeed. Body kits usually are poorly designed and result in disturbances in air flow, thus increasing drag.

[fpv_gtho]

Its possible. Wont happen with your average kit, but its possible with a front spoiler, rear spoiler and rear diffuser you'll add more downforce to the car than weight. As you said, if its a reputable company, if theyve actually designed kits specifically for cars, done computer modeling or wind tunnel testing. Its definately not beyond the realms of possibility.

The manufacturers aero testing doesnt mean the car is guranteed to be stable. It just means theyve made an effort to try and fix some of the problems the natural design may have had.

[Matra et Alpine]

A street car aerodynamic design is a compromise to handle the usual things we meet on streets - kerbs, speed-bumps, rough ground, steep ramps in car ramps etc etc. This means the "body" parts can't really be any lower than the lowest part of the chassis.

SO a well designed aero package can improve stability at speed at the "cost" of high risk of damage on "real" streets

[LaSarthe]

IMHO, body kits, when properly designed and installed will only serve to mitigate the lift at speed that 99% of road cars experience and not produce useful downforce. Just from the basic shape of a car, one can derive the shape of a lift producing wing. In order to produce downforce in any significant measure, the car needs to be designed from the start for that very purpose.

Firstly, the question must be asked; What is downforce? Certainly we would all like the car to weigh more at speed than at rest for track/competition purposes and that is precisely what the result of downforce is understood to be. However, there is one and only one condition that must be met for the generation of that effect: the airflow velocity underneath the car (or downforce generating bodywork) must be greater than the airflow velocity over it. The difference in the over/under airflow velocities is reflected in a difference in air pressures. Higher velocity = lower pressure. Lower pressures underneath the car means a greater suction force applied. Therefore, in many cases, what you can't see (the underbody, front/rear diffusers) is far more important than what you can (spoilers, flaps, etc.).

Downforce is not a bolt on modification, though the reduction or even elimination of lift certainly might well be. Normal road cars are simply too imprecise to properly "nurture" the low pressure area underneath themselves necessary for downforce. Minute adjustments to ride height, rake angle, and spring rate, all of which are demands placed on the suspension engineer and not aerodynamicist, are capable of producing large changes in the attitude of the car.

I would agree to coolieman's suggestion for grippier tyres if you want better performance. There, the question is asked; "what part of your car actually touches the damn road?"

[Quiggs]

I would agree to coolieman's suggestion for grippier tyres if you want better performance. There, the question is asked; "what part of your car actually touches the damn road?"

My subframe. Sometimes the oil pan and rockers.

[drakkie]

My subframe. Sometimes the oil pan and rockers.

Need better suspension ??? I'd watch out with the oil pan, if there is some kind of shard thingy it gets stuck behind, you have a severe problem. My uncle has this story that he drove a 50.000€ Maserati's oil pan off once. He was barely able to leap home. Total cost 35.000€.

[NSXType-R]

Drakkie, I think you took that a bit too seriously.

Sarcasm perhaps.

I'm not sure. C-West is an aftermarket company that might not have much expertise. What happens if it came from Nismo or Mugen for Nissan and Honda parts? They should be quality parts there right?

[Coventrysucks]

I concur - I doubt there are many bodykits available that provide downforce.

Maybe if you are talking about the massive wings available for the Ariel Atom.

In the overwhelming majority of instances, the best you can hope for is lift reduction, which seems unlikely unless the manufacturer has access to a wind tunnel and some aerodynamacists.

What you will probably end up doing is upsetting the lift balance - the ratio of lift generated over each axle - which is probably not desirable - as early Audi TT owners might attest.

I suspect that the additional drag would, in most cases, increase lap times more than than the lift reduction would lower them.

Manufacturer supplied aero kits will probably have had some sort of evaluation, although I have heard that in some cases the science has not agreed with the marketing department's desire for big flashy wings.

Underbody enhancements, such as diffusers, will probably do more than a wing (Renault Sport Clio), but will be dependant on suspension and ride height, which, knowing the sort of people who think bodykits are wise, will already have been interfered with.