Comparing two tires for purchase both extreme performance summer tires in the same size (215/40/17) one is 8.7" section width 7.3" tread width the other 8.6" section width and 8" tread width. Does that mean the contact patch on tire two is more than half an inch wider than the first tire? And to what extent does the overall diameter play in contact patch?
Yep, that's why it's so important to check the actual specifics of the tire rather than going by the standardized size. Check out the specs. on the 225/40-17 Hoosier A7!
Mathematically, the overall diameter plays a negligibly small role in contact patch. Tire pressure plays a larger role but it's unlikely that you're going to air down, as do the 4WD guys, in order to increase contact patch on a street tire. Profile is in the mix, too, because a tire with a taller profile is more compliant. I wouldn't take any of this into account when picking a street tire - the widest tread with is going to offer the largest contact patch.
Also, I believe that most manufacturers design the 205/40 around a 7" wheel and the 215/40 around a 7.5" wheel, so you might be better sticking with the stock size if you're on stock sized wheels.
The online chat guys at tire rack are awesome; ask them what they think. You might need to use a VPN to make it look like you're coming from the States. And, when you get back, buy some tires from them as a thanks!
