Originally Posted by Geezer
From a purely scientific standpoint, aka physics, and with all things being the same (especially both tires supporting the same weight and having the same internal air pressure) but excepting the overall diameter, the size of the contact patches will be identical. The contact patches will, however, vary in shape.
this is my belief.
wide tires have wide but short contact patch. narrow tires have narrow but long contact patch. total area is the same
contact patch area in sq.inch is as simple as total vehicle weight divide by 4 tires divide by PSI in the tire.
you can get the approximate contact patch length, by divinding the area by the tire width.
ex. 2800lb car / 4 / 35psi = 20 sq inch per tire
with my 275 wide hoosier race tires (11in), the contact patch is 1.8" long.
with my 195 wide snow tires (7.8"), the contact patch is much longer 2.6"