I am running S-02 tires, stock size/rims on my '02 S2000. I picked up a screw in the edge of the rear driver-side tread that flatted it and tore it up pretty well. These tires are at about 50% of treadwear. Since the tread depth is so minimal on this tire, can I get away with replacing just the one rear tire, or would that cause any risk to the differential?

 

replace both

 

I would replace both and keep the good used one as a spare in case you have the same situation in the future, then you can have 2 50% tires later on.

 

Ditto