it says that one of the Wheel/tire special combos is the JSM with the 235/40/17 tire size. Won't the sides be a little soft since the wheel is 7.5" width as opposed to 8"? Just wanted to know if performance would be adversely affected...15.4 lbs is a light weight after all for a 17" wheel!
I've had 235/40-17 tires on 17x7.5" Enkei RPF1 wheels (ET48) for almost 20k miles - they are fantastic in every sense. I've autocrossed them, too. Certainly, you'll get a fraction less responsiveness than if you used an 8"-wide wheel, but I doubt seriously you'd notice the difference in everyday driving. The added benefit is rim protection - I can pull right up next to the curb without worrying about my rim.
rpmchris, thanks for the reply. I was actually considering the RPF's in black (tirerack.com) but when i saw that they were 7.5" i was disappointed, as i wanted to run the 235/40's. (too bad the 225/40 size is so rare!)
May I ask what tire brand and model you are running?
I'm running Goodyear F1 GS-D3 tires, arguably the best dry AND wet summer performance tires around (on my Marble White MX-5, an old pic on page 4 of the Enkei RPF1 thread). They are probably 1/2 used now, with 20k on them - I'm happy they've lasted this long (including 3 autocrosses last year), considering they're relatively expensive.