Discussion
quote:
Can anyone tell me how much the track of the car (width wheel too wheel) alters the handling i.e if you were to reduce or increase the track by 20mm, front or back, what effect, and how much of an effect this would have? sorry, trying to understand set ups a bit more!
Looking back at the length of this reply, you're probably going to wish you hadn't asked this question!
20mm in the geometry of the hubs can make a huge difference - if you were to stick spacers in there or fit wheels with 20mm different offset, you would change the behaviour of the steering (tramlining, feel, kickback) dramatically, and potentially reduce the life of the wheel bearings and so on. There are other ways to change the track though which don't do this.
The effects of track changes are relatively small.
In theory, with a wider track, the roll input from bumps in the road are reduced, so you get a slightly more comfortable ride and slightly more grip. To be honest I think you'd have a hard time measuring the impact of 20mm let alone feeling it, and I'd ignore this effect.
What does matter a bit more is a wider track results in less lateral weight transfer when you're corning. Lowering the car's center of gravity has the same effect. Racers want to reduce the lateral weight transfer because it (the weight transfer) reduces the amount of grip you get from the tyres. At first glance using the physics we learned at school there's no reason for this, the total grip is simply the weight times the friction coefficient between the road and tyres - it doesn't change just because you've moved the weight around a bit.
But when you look into it a bit further, you find that the friction coefficient of the tyre is not a constant - the more weight (and hence pressure) you put on it the lower the friction coefficient. Put another way, the grip does not increase linearly with weight, doubling the weight produces slightly less than double the grip. When lateral weight transfer occurs you end up with the heavily loaded outer wheel providing a slightly lower friction coefficient, and the lightly loaded inside wheel producing a slightly higher one. You lose more grip on the outer wheel than you gain on the inner one, the net result is less grip. Not a huge effect, but definitely enough to be noticeable, and it is very important when you're tuning a car's handling.
Incidentally this also is why people tend to fit big wide tyres to sports cars, and is also how anti-roll bars and tyres sizes come to effect the car's handling. A consequence that is often overlooked is that the less weight you have on the wheel, the less sensitive it is to weight transfer (the tyre works in a more linear region of the grip curve). Over-tyring a car can make is impossible to tune the handling, because it renders the anti-roll bars ineffective.
Having said all that, 20mm is an insignificant change to the overall width and I don't believe you would notice the difference.
BTW in case you're wondering about the S1/2/3 and S4/V8S track change, I believe the reason is that the rear uprights were changed to disk brake versions which happen to stick out more, not to improve the handling. But the S4/V8S also have a stiffer chassis and different spring and damper rates which do affect the handling. I noticed a huge improvement when I changed from the S2 to the V8S, the V8S felt much more stable under braking and more composed over bumps.
Sorry for the boring techno waffle, but you did ask!
Cheers,
Peter Humphries (and a green V8S)
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