airkewl

I have a 99 C4 and it came with 7.5" and 9" x 18 turbo twists with 225 40 18 FT and 265 35 18 rears (Continentals SportContact 2). I am replacing the wheels with 8s and 10x18s (turbo twists). I know that the C4 is sensitive to tire sizes front to back, as the rotation difference determines the amount of differential lockup. The later C4s (2003 I think) used 225x40 fronts, and 285x30 rears. Is that model year specific, as in the later models are programmed differently? Or is that a permissible amount of difference in circumference (the 285x30s actually have a smaller height and circumference than the fronts).

Also, I have a friend at a Mercedes dealership, and he has offered me a free set of brand new SportContact 2's in 275x35x18 that were take-offs (E55 I think). If I wanted to keep the same circumference ratio as now, I could run 235x35 fronts and be just about bang on what the ratios are now front to back, although they both would increase height and circumference moderately. But that would also keep the rears slightly taller than the fronts, which seems like the right look.

So, can I run tire combinations outside of the front to back ratios that came stock? And do you think the 275's are a good choice, either with 225x35 or 235x35 fronts. I know Continentals would not be most people's choice, but the price is right.
Tony