1) It would be nice to go with the same size all around (so that I can rotate them all) - given that, my research pretty much points to 235/40 tires as the largest that will fit (front and back) w/out fender rolling or spacers, assuming I go with 17x8 wheels. Does this sound right, and does the fact that my car is lowered by 3/4" or so by Eibach Pro-kit springs affect the fitment? I haven't got a definitive answer on this from the shops I've called so far, so I'm wondering if any of you have empirical data.
2) Since the stock tires I've been running with are 245/40 in the back, will going to 235's back there cause any noticeable/significant traction loss? (Btw, I'm planning to go with an R-compund tire, so maybe the decreased track width will be offset by the extra stickiness of the new tires over the Michelin Pilot Sports.)
3) If I decide to stay with different sizes on the front than on the back, and stick with 245's in the back, will it be OK to go with a 17x8 rim (as opposed to the stock 17x8.5), or should I stick with a 17x8.5 wheel back there? I know that there are issues with having a tire that's too wide for the rim it's mounted on. Having to get a 17x8.5 would affect what brands of wheels I can go with, e.g. BBS rc does not apparently come in a 17x8.5.
4) Again, if I stay with with bigger rear tires - will 255/40's fit? I've heard they will, but again I'm not sure if the lowered state of the car affects it. If 245's are OK on an 8" rim, will 255's be as well, or would I then definitely be pushing the envelope?