225/60s on stock 15"x7"s?

If you do that the diameter of the wheel will increase and the speedometer/mileage reading will be off.

I'm running 215-65-15's on the SDL. The tie rod clearance is about 1/2 inch. If you go to the 225's, you will be quite close to the tie rod. I don't think the wheel will actually hit it, but, it might be too close for comfort.

If you go to a 225/55 the rolling circumfrance will be almost exactly the same as the standard 205/60. You will not notice a difference in speedo accuracy.
Rod...

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

original size: 205-65/15

size 1: 215-60/15 speed reading +1.3%

size 2: 225-60/15 speed reading -0.5%

size 3: 225-55/15 speed reading +2.9%

so if you are moving up to a 225, stick to 60 sidewall as it will remain as close as possible to the car's original speedometer setting.

I think the question pertains to the fit of a 225/60 on a 7 inch rim. I'd say its fine, as I have had 225/60's on 7 inch pontiac rims, and the fit is within the limits of the rim.

My 1990 560SEL registers 67 1/2 MPH when I am actually traveling 65 MPH. How do I know this? I checked it with my handheld Garmin GPS and the faster you are moving the more accurate the device becomes and is sensitive to .1 MPH.

A cool way to confirm your speed.

Gary