Does anyone here replace 2 rears or something to every 1 front? I do a lot of commuting on my bike and the rear has no tread left at all in the center. The front tire still has roughly 4 millimetres of tread left. Is it okay to replace just the rear and not the front? I would like to replace both but I can't really afford to do both because I want to goto another track day in August. The tires on my bike right now are Michelin Pilot Sports and I would be replacing the rear with another Pilot Sport.