Well I bought one tire to try it out on my spare rim Kumho Ecsta 4x 255/35-18 on my 18X8 et38 Rim... I mounted the tire and tried it out on the front and it fit with no rubbing at all!! I took it for a test ride and we also pushed front end down, and no rubbing. Tire looks good on the rim, it is a hair wider then the rim but should be good if I accidently hit the curb. I think 245 would be the perfect fix/look but I think the 245/40-18 (25.7 diameter) is to tall...The 255/35-18 is 25 diameter and that is stock height. On my wife's car when going to a 25.4 diameter tire it seem to make the car feeler slower and I am afraid that a 25.7 will be even worse.
So now that I know they will fit, here is my next question.. I have original M3 front rims that are 18x8 et47 I believe. Would it look better to have 18x8 et47 in front and 18x8 et38 in the back? If I am not mistaken, the back rims look more sunken into the wheel wells then the front. So would the two different offsets look better and would it handle alright. I know there is a lot of talk about square setups being better. Would this still be considered square with 255/35-18s on front and back? Thanks for everyone's input!!!