Originally Posted by dcstep
I'll be using 30-series, 18" tires for my autocross set up next year. I'll be going to a 10" to 10.5" rear wheel to allow as much tire as possible back there, to gain acceleration, since AX is mostly run in 2d gear and I now spin my 19" wheel/tire set at will anywhere on the course. The low profile will give both a wider contact patch and stiffer sidewall. The front tires will also be 30-series and about 20mm narrower than the backs, to maintain balance.
The added advantage of 18", 30-series tires will be that the final drive ratio will be slightly higher numerically, improving mid-gear acceleration.
For street, I'll be staying with the 19" factory option, forged wheels in summer and 18" factory wheels, with snow tires for winter. I think these are the best compromise of ride and handling, where my AX setting is aimed at acceleration and handling with no concern for ride.
Sorry, how do you figure the 18 x 30 tires will give you a lower profile side wall?