When cruising with some friends yesterday in the new turbo M3 it became readily appearant I need stickier rear tires. When I punched it in second gear the rear 235/40-18 S02's spun as my friend slowly pulled ahead of me. I could even feel the tires slip when punching it in 3rd gear at about 60 mph.
I currently have Breyton Softline 18x8.5 with 235/40 S02's front and rear.
I am thinking about buying a pair of the new S03's for the rear, will an S03 in 245/40 fit the rear with no problems on a lowered M3 with Bilstein Sports and Eibach pPro-Kit springs?
Can someone recommend a better/stickier tire for the rear?

235/40/18 is already taller than stock. 245/40 will throw your speedometer off. I'd go with 245/35/18 all around. Toyo Proxes T1 have it on that size and they are excellent tires. www.treadpot.com is a good place to get Toyo tires.

OK, thanks man.

Go with 255's in the rear. They will fit if you do some fender rolling