Hey, guys. I'm getting ready to get r-compounds for autocross. I'm going to put them on my 17x7.5" wheels that I use for the winter. I'm doing this as a cost-saving measure and don't believe that it will cause any detriment to speed, unless I can't fit as much tire on them.

I understand that the stock wheels are 18x8", is that correct?

Is there any way that a 275/40/17 Victoracer will fit on my 7.5" wide rim? I was running 245s on my 7" wide stock wheels for my Z3, and they fit ok. I'm increasing the width of the tire more than I'm increasing the width of the wheel here, though (by a little more than double).

Nobody makes 265s in 17", so I drop down to 255s. I can get the Victoracer V700 in a 255/40/17, which will be 2.5" shorter overall than stock, effectively lowering my gear ratios. I could go with a V710 in a 245/45/17 that's only .8" shorter than stock. So, Is the V710 better-performing enough to offset it's 10mm narrower tread width? Will the tread wear be at least as good as the Victoracers?

Thanks, folks.

Of your choices the fastest will be the 245-45 V710... The victoracer will last the longest, but the V710 is durable. Mine have about 55 runs so far. It will not be as fast as the 245-35-18 due to diameter and sidewall flex but it is a good way to get started. btw you do realize this is not B stock legal and you will be in SP or SM.

Also not sure how you did your math on tire size:

Tire Size Sidewall Diameter Circumference Rev/Mile Difference
225/45-18 4.0 in. 25.97 in. 81.59 in. 777 0.0%
245/35-18 3.4 in. 24.75 in. 77.76 in. 815 -4.7%
245/45-17 4.3 in. 25.68 in. 80.68 in. 785 -1.1%
255/40-17 4.0 in. 25.03 in. 78.64 in. 806 -3.6%

Of course with the 17's you can't run stock class.