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Tromac · 07/02/2012, 02:06

(07/02/2012 01:53)Jashdown Wrote: One problem with that. How does the length of the contact patch shrink? I understand the change in width, but the length is not right. The diameter of the tyre does not change, therefore the length of the contact patch remains the same.

You're simplifying things far too much though. I won't be able to explain it here in detail (it's too difficult to explain it in text, i.e. I'm being lazy), but as I said tyres are actually unbelievably much more complex than most give them credit for. Making a tyre wider will effect other properties such that the contact length will consequently decrease. Much the same as how reducing the tyre pressure will consequently make the patch larger. You're not only changing one property of the tyre but many.

Jashdown · 07/02/2012, 02:17

The length will only decrease relative to the width (if the width is increased and the length remains constant, then the length appears to shrink).The length can literally not change if only width is changed, length remains the same and only the tyre width is changed. The contact patch gets longer and wider when there is more force applied, and thinner and shorter with less force applied, but that's only due to deformation. If you have an ellipse, and then grab the edges closest together and stretch them out, then that is the same as widening the tyre, the length won't change, it simply can't. Does this same rule apply for cars?

sir.b · 07/02/2012, 02:18

I think it's because the tyre will deform differently due to weight on it. If you're putting 500kgs on a tyre, a wider tyre will deform less length wise than a narrow tyre will so the contact patch will be wider and shorter.

Justin.

Jashdown · (This post was last modified: 07/02/2012 02:22 by Jashdown.)

Now that I think about it, the length of the patch will decrease because the force applied to the ground through the patch is spread over a different area. Is that what you're saying?

(07/02/2012 02:18)sir.b Wrote: I think it's because the tyre will deform differently due to weight on it. If you're putting 500kgs on a tyre, a wider tyre will deform less length wise than a narrow tyre will so the contact patch will be wider and shorter.

Justin.

Haha yeah that's what just occurred to me. I see what Tromac is saying now.

Gotcha!