I've got a set of 15x6.5 Rota C8's, what's the widest tire I can run safely for autoX?

 

Well after reading around I'm either going to stick with some 205/50/15 or maybe try some 215/50/15.

 

205/50/15 is the best size for you.

 

If the choice is between 205/50-15 and 215/50-15, stick with 205/50. There are lots and lots of great tires available in 205/50 (e.g. Azenis, and lots of R comps) and they are much better than the few tires available in 215/50, which are nowhere near as good (even the best is only the BFG Sport, which is a fairly mediocre street tire).

 

225/50's run fine on on my road race car on my 6.5's.