I would consider a 235 and lower your profile. I am not sure what size rims you have but for argument will will say 16's. You may have 205 or 225 width already. If a 205 then a 55 profile, and for 225 a 50 profile. I would suggest something like a 235/40/16 or a 235/45. Possible even a 245. This should help grip and lower hiegh of the tire and rim combined. This should help improve excelleration (slightly) and maybe even drop a little weight. Obviously I am assuming that these would only be used for Auto-X. Need more info, send me a PM and I can help clarify what I have just rambled about. Good luck
edit: 255 is probably to wide for the front, but may be possible.
A non-M E46 can usually fit a 255/40/17 on all 4 corners with the proper offset. The problem is that the offset that clears the fender lip in back will rub the strut like crazy in fromt. For the serious autocrosser, a set of 4 17x9s with an offset around 50mm, a pair of spacers (15mm?), and longer lugs for use up front with the spacers would go really well with some 255/40/17 Kumhos. If you run with the big boys and use Hoosiers, 245/40/17s are at least as wide as Kumho 255/40/17s and are the only way to go at Topeka.
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