I have two brand new Michelin Pilot MXX3s that are 235/40/17. I can buy a pair of Bridgestone Potenza RE070 225/45/17s for $40. I know that they will be about .5" different diameter. Is this a problem? They will be run on 4 17x8.5" Contour Replicas on my 95 M3. Which should I run where? I know that the 235s should be on the back because they are wider, but I don't know whether the tread or sidewall on the two different tires would be better on the front compared to the back. I wouldn't think that less than 0.5" in width would make a huge difference in look or handling. Or should I just keep looking for another pair of 235/40/17s?

I would look for another 235/40 size tire. If you must, run the 225/45 up front, seems like to good a deal to pass up. Anyhow, the OEM staggered tire sizes for E36 M3's were 225/45-17 and 245/40-17 on 7.5" and 8.5" wheels respectively