Originally Posted by ReRisenAngel
I'm not getting all gangstered up I can tell ya'll that for sure. I'm simply trying to ascertain the widest tires I can fit so I can weigh possible performance advantages. I won't lower the car unless I believe it provides a higher advantage than the wider tires, since I do track for lap times.
Anyways, so I think I got it. 235 40 18 on 18x8.5 with an offset of 37 should provide the widest tire with the least change properties, BUT it may rub at the lock-to-lock points and probably will rub when in a tight turn unless I significantly stiffen the suspension.
For the rear if I go to 285 30 19 on 19x10 with the same offset of 22 that will do about the same. Overall effect is a slightly lower top speed because of a slightly smaller diameter tire but I'd have allot more rubber on the pavement at any given time.
Does all that sound right? And if I put 18x8.5 with an offset of 33 on the front, and then put 245 35 18 tires would that pull the wider tire away from the inboard wheel well and push it a little toward the fender, possibly enough to keep from rubbing?
EDITED
That's pretty much the story.
The tire sizes you mention can be mounted on the OEM rims, no problem. The OEM's are 18X7.5 and 19X9, BTW.
Keep in mind that if you change aspect ratio, you should do it on both front AND back, or you'll end up aiming your headlights into the sky. The chubbiest tire combination that should be safely considered for mounting on the OEM rims are:
255/35R18 front and 285/30R19 rear.
Note that BOTH aspect ratios are down one notch, but BOTH tires are darn close to OEM tall. Also note that you WILL experience a little rubbing up front at full turn lock, but it's tire rubber against the flexible plastic wheel well liner; no big deal.
Not too many manufactures offer tires in BOTH sizes, tho.
Post some pics when you're done! Good luck.