I'm trying to match up the sizes for ADR M-Sports 18", and Goodyear Eagle F1 GS-D3's.

I don't want to have to roll my fenders, or do any extra work to get my tires and wheels to fit. I don't want to stretch the tires either, as I heard it means your wheels get more exposed to potholes and such.

For the M-Sports, I wanted to use 18x8.5 for fronts, and 18x9.5 for the rears. I believe this is wider than stock, which would be nice.
I don't know what size tires support that without stretching, so this is where I need help. Also on the ADR website, under specs for the M-Sports, there is something called PCD. They vary from 5x112, 5x120, and 5x114.3. What do those mean?

Stock tires (I have a 2006 enthusiast) are 225/45R18 front's and 245/45R18 rear's. I don't understand how I am supposed to figure out what setup will work with 18x8.5 and 18x9.5's. What's optimal for wanting widest tire, without going low-profile, and not having to roll fenders or anything?

 

your bolt pattern is 5x114.3, I suggest a tire size of 255x40F and 275x40R.

 

255x40 and 275x40... won't that mess up the spedometer because the aspect ratio is moving from 45 to 40? (I have no understanding of tires.. excuse me..)

 

the speedo is hooked into the trans (essentially measuring the rotation of the rear tires). however the actual speed difference with the setup I recommended is 0.1% which is nearly indistinguishable on the speedo.

http://www.miata.net/garage/tirecalc.html (look here)

 

The wheels are the same size as the NISMO wheels. Use the NISMO recommended tire sizes.

 

yeah hell if your fast enought your eletrionic MPH dont keep up anyways haha!