Originally Posted by
Burton
Some of that makes sense except that a 700 x 32c tire isn't a 29er. It's Imperial measurements are actually only 28 x 1 1/4 inches. Even a 700 x 50 isn't a 29er. It's actually only 28 x 2.00 inches. Something in the order of a 57-622 would give 29 x 2.25 inches.
I picked those numbers at random to make the point that the width of the tire is irrelevant to the size of the contact patch.
So yeah, in similar tire widths and with similar tire pressures, a 29er would definately have a slightly greater contact patch.
No. The surface area of the contact patch depends on two things, and two things only:
(1) The weight on the tire
(2) The inflation pressure of the tire.
People typically run fat tires at lower pressure, which gives a larger contact patch, but that is because of the lower pressure, not the geometry of the tire. Fat tires do make it
possible to run low pressures: try running a 700x23c tire at 30 psi, and you'll pinch flat as soon as you sit on the bike.
It also seems reasonable that frame geometry is going to have an effect on the distribution of weight between the front and rear tires, and therefore things like rear-wheel traction on climbs.