i was running 225/60/15 and was really happy with the look. i had to go all the way to 205/60/15 ! you may not have as much trouble as i had though...thanks to input from another thread here i learned to i foolishly trusted the sales rep at summit to sell me the right centerlines. i have 15" autodrags with the 3 5/16" backspace. i was told that with front discs i should have bought the 4 7/8" backspace. i feel that should be the difference in being able to fit 215/60/15 in front. (i am unsure that 225 would work though). i have 275/60/15 in the rear and want to balance the look with as large a tire as i can go in front.
http://www.miata.net/garage/tirecalc.html
a cool tire size calculator.....