Quote:
Originally Posted by Michael Hill
I think there are a couple of misconceptions here. There contact area will actually not be increased by that much with a wider wheel. It sounds odd, but the pressure that would be applied over a thinner wheel is now spread out over a wider one. That lower pressure doesn't allow the tread to expand as much along the wheel. However, because your width is greater, the contact area is roughly the same.
Second, drag racers have wide tires solely because of heat. You need big tires to dissipate it all. The stickyness that happens does, in fact, increase traction because it now brings in adhesion (your coefficient of friction is now >1). It literally is pulling the car down when this happens. However, in our situation, our wheels aren't producing near enough heat to do any of that.
Another thing to remember is that friction is very inexact. It's been seen in some circumstances that the coefficient of friction can change with respect to load (which goes against classical friction theory). There may be many other factors that come in to play as well.
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In pneumatic tires or equivalent, this is true. Widening the tire will not change the contact patch, the patch will grow wider but shorter. Thus the way to increase the contact patch is to make the wheel a bigger diameter. I need to dig around to find the book I referenced this from.
However, for solid wheels I do not think this is totally true. I think it behaves more like a rack and pinion. I think the contact patch is small, so to make it bigger is to make the wheel wider. As with gears, you can't make more teeth mesh, but you can make the teeth wider to hold more load (assuming the DP is constant). If your "teeth" on your wheel can hold more load, you have more traction. Of course this can't be totally true because the wheels sink in the carpet a bit.