>RX7 rims fit with a little backspacer. I used 1/4" for mine >so i could keep the centercaps, but 1/8" will get you by on a >225 wide tire.
Yes, I use a 1/8th inch spacer on my rx-7 rims with 225 tires, and I have no clearance problems.
>Beware, they are prone to cracking.
The "early" 3rd gen RX-7 rims are supposed to be prone to this. I think mine are the early version, but even with drag racing on them for a whole season, driving to and from the shootout, and autocrossing at the shootout as well, I have had no problems.
You defenitely would want the RX-7 rims for autocross, they are very light (about 14 lbs) and 16 by 8 inches wide (excellent width to support the tire in autocross, whether you use a 205 or 225).
You can get the RX-7 rims pretty cheap, I've seen $500 with tires, but they are getting harder to find, alot of 1st generation DSM owners I know are picking them up.
