Quote:
Originally Posted by Alan L
OK, I'll bite. How come the lower pressures with wider tyres? And how do you get same contact patch with narrower tyres at same pressures? - same weight on less rubber = more squat?
Sometimes it seems easier just to turn the key and mash the pedal.
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Well, Alan, we are all going to "mash the pedal" regardless, so that part is a given.
First of all, to state the obvious, the weight on a particular corner is the weight on that corner - let's say 800 pounds. So let's think of the tire problem in terms of 2 extremes: a 205mm wide street tire, and a 315mm wide track tire. Inflation pressure is, say, 25 psi.
[1] The 205mm tire will spread its contact patch as wide as possible, limited by it's tread width and sidewall, which will bulge too (to which I shall return shortly). That 800 pounds has to be supported, so once the maximum width of the narrower tire is reached, the contact patch starts to e-l-o-n-g-a-t-e front-to-rear, and eventually enough rubber is on the ground to support the weight. Not having to do with the AREA of the contact patch, per se, but that bulging sidewall now plays havoc with keeping that contact patch in a stable position.
[2] By contrast, the 315mm wide tire will likewise spread its contact patch as wide as possible, limited by it's tread width and sidewall, which now offer approximately 50% more "spread". The sidewall is much happier, being better able to remain more "upright" between the wheel bead and contact patch. Will the contact patch elongate front-to-rear also? Of course - SOME.
In short, the 800 pounds squashes the wider tire down on the pavement in a different way. And, yes, we have yet to talk about HEAT in the two extreme sizes of tires.
Ed