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NobodySpecial
#2
Nov25-10, 04:32 PM
P: 474
The static friction of the bike tire and the road doesn't change - but you don't care about that, the part that is fixed in contact with the road isn't doing any work.

What does change is the energy needed to deform the new bit of tire as it comes into contact with the road (to create the flat contact patch) this energy is then mostly lost as the tire springs back. Since work is force * distance it is the amount you have to compress the tire that matters.

In a solid (or high pressure) tire there is very little change in shape - and what change there is 'springs back' as the tire rotates out of the contact patch putting some energy back into your forward motion.