IT rules require that you run stock wheel size for the make and model. However 13 or 14 can be substitued with 15's. ITR allows up to 8.5" wide wheels but keeping the resultant tire sizes under the fenders should prove difficult at best. I'd bet 245 would be the limit with a generous backspace modification.
Sold my Spec so I can't test for you.
James R.
James Rogerson - SowDiv; CSR #32, ASedan #2 and XP #46
Men that like golf are unhappy at home and unable to have meaningful relationships with women. - Joseph Heller