Originally Posted by
bobn
I still can't see how putting more rubber on the road lowers the rolling resistance. It would seem to me that wider tread would create more friction than a skinny hardily touching the road tread, thus making it harder to keep in motion?
The size of the contact patch is equal to the weight the tire is carrying divided by the tire pressure.
So if you have a skinny and an fat tire at the same pressure, they have
the same size contact patch. This is what most people miss.
Now think of how the tire deforms to make the contact patch. The wide tire is wider, so it needs flatten less of the circle to get its patch. The narrow tire, however, need to deform more of the circle to get the same size patch. So the narrow tire deforms itself
more than the wide tire. And this is why the narrow tire has more rolling resistance than the wide tire (assuming the same material and air pressure).
Cheers,
Charles