For those of you who put bigger tires on your stock 18's!!
 

Did you run into any problems running a bigger tire on a 8.5 inch rim? Any benefit to running the bigger tire or should I stick with the stock sizes?

What would be the ideal size to put on the stock 18" rims?

I was thinking 245/40 fronts and 255/40 rear.

255 should be fine i believe. Ive heard of someone putting 275 hoosiers on their stock wheels, which seemed wayyy off.

I have 275/40/18 on my rears with absolutely no problems. Michelin pilot sports. Understeer was increased because of contact patch difference between f/r but traction on take off is great.:D

Best thing to do is to keep the final diameter of the wheels correct. 255/40 front and 275/40 rear is the best... I dont know what is going to happen with the 8x18 wheels and the 275/40. No problems for those with RAYS (8.5x18 rear).

Do a 265/40 on the 8.5" rear, it looks good...

Yea, I had 275-40's on stocks....no problems

265/40's Rear, 245/40's front. I don't have pic's of the fronts but here are the rears.

No problems at all and much better bite.

If you like a particular tire, and its available in stock size, then get the stock size. If the sizes are limited, plus or minus 10 mm should be fine.