[330iGt]

Go for the 235's on a 8.5 wheel, and the 255 is ok if you want a staggered setup. The difference is only 1% or so, but when your rear tires are near 30% and your fronts 70%, the difference is much greater than the original 1%.

But of course, 235's would be most track friendly.

 

[330iGt]

I should have eleborated...

If you are a performance oriented person, stick with the 235's all around. The extra width in the rear will make the car understeer quite a bit and you don't really need anything larger than 235's, because our cars do not put down that much power to create massive tire spinning.

If you are more show, then the 255 in the rear should be just fine with the 235's up front. The difference of 1% is the difference between the 225's and 235's, which is really negligible, if you take into account that percentage rises just by having uneven tire wear in the front and the rear.