Do you have a 98-02 4cyl?

http://www.miata.net/garage/tirecalc.html

I want to put 215/60-15 Sumitomo HTR-200s on my stock 15" steelies and use them for autocrosses, so I don't have to shred my expensive 18" Yokohamas.

Will the wider tires help performance, and will they fit on the stock '02 LX I4 steelies? Are the stock steelies 6.5" wide?