I autocross my SRT and have 18's all around. I think the back could go down to 17's, but the fronts look like they might have a problem with 17's (depending on the style). As far as changing wheel size with autocrossing it will kick you out of stock class. I looked into it when I first got the car and found that going to 18's all around popped me into ASP. So I am running against some very well set up Corvettes that kick my butt, now that could be just the driver, though :-).

Thanks,

Michael