I just changed to 17" wheels to get a softer and quieter ride (MB wheels). You can go to www.Miata.net for tire info. Put in you stock size and then compare other sizes to get the same Dia. as stock. I need to now install a spacer in the rear to get the wheel moved out some, I guess I'll have to put on one the rear wheels back on to measure to the fender to see what size spacer I'll need. The bolts were a little to long and when I backed out of the garage, there was a pop and something gave in the rear hub. Everything works (I think) and now something is rattling in the hub. I took the bolts back out and there was a little stuff on one bolt thread. I'll have to do alittle more research, but I will not be driving now until the weather is better and they stop putting all that anti-freeze on the roads.