Originally Posted by flaco

I use Sheldon Brown's 'put the good one in front' rule. When the back tire gets squared off, put the front tire on the back, and a new tire on the front. For me, front tires wear very, very slowly and I would end up leaving the front one on for years if I didn't move it to the back. I don't want to ride on a super old front tire, even if it looks unworn.