I had been Proxes (s1r's?) They have been discontinued. I had to replace one rear unexpectedly. I got the replacement for the s1r, i think it's called t1r. 255/35/18... For some reason it seems to be more stretched. Can I run wider tires?

 

How wide are your rims and what are your offsets? your question is impossible to answer without this info. I would also double and triple check that your rears match exactly. You can destroy your differantial if they are significantly different diameter, not to mention serious handling problems(potentially)

 

On the SP1 the 255/35R18 is the widest that I would go with. Even that size does some times rub on the rear fender.