I just did that title to get your attention.
Down to business. im looking at 18x8.5's (which are sized to fit) and looking at a 275/35/18 on the rear and a 245/40/18 on the front? out side of possible oversteer and a crappy ride any other laws of physics that im going to be breaking unknowingly??
Also, correct me if im wrong but if a 275/40/17 (25.66 diameter) fits without rubbing on the car, then a 275/30/18 (25.7 diameter) SHOULD clear if i have no rubbing, at full lock rubbing is alright to me, being if im at full lock at speed im about to die anyways. So anyone with 18's help me out

 

You are correct about the 275's in the front. With actual sizes (wheel and tire) matched up you will have the same results. Should work providing the fronts have the correct offset/backspacing. Another thing to keep is mind is your stance. What kind of drop do you have? One thing I'm not sure of is tire sizes for those wheel sizes. Not sure if a 275/35/18 will fit on a 18x8.5. When you run less sidewall, the fitments become less forgiving as far as width. Check the tire manufacturers and if they say it'll fit then go for it.

 

i wanna know the same thing, if i can ut on 265/40wr-18 on a 8.5" wide rims. i'm looking at 18"x8.5" rims for ,my car. after i finish the install on my exhaust

 

a 275/35 fits perfect on a 9.5 i wouldn't try to put them on any other size rim.