Need some advice and answers.

First answer: Wider is taller, so when you go with a wider tire for the rear, you need to use a lower profile to keep the same ride heighth. If you used the same width front and back it wouldn't be necessary.
Second answer: more than likely you will have a problem. 315 rears are about as big as you can fit under a pony, and with the Eibach drop, you have a 97% likelihood of rubbing. I am going with a 305 rear tire on 18x10, so I know I won't have to worry.
Hope that helps, good luck

315/30/18's will clear with a sportline kit. i have seen it in person.

The taller tire is used on the front to compensate for the skinnier width. The second number on any given tire size is the aspect ratio of the first number (width in mm). Here's the formula to figure the overall height of a tire...



For example, to get the diameter of the O.E. tires (245/45ZR17)...

(245x.45)x2
.....25.4......+17 = 25.68 inches

Now say you're going to 18s...if you get a 275/35ZR18 in the front, the diameter is 25.58 and a 315/30ZR18 rear would be 25.44, which is about as close to the same height as you're gonna get, both with each other and with the O.E. size (so as not to screw up you're speedometer).



As for the rubbing, I've seen it done and I've also heard of problems. I would imagine that any difference would be from the offset of the wheel. As long as they stick out far enough, you shouldn't have any issues with rubbing on exhaust, shocks, the trunk, the back seat, etc...(after all, those things are friggin' HUGE)

SaleenGT2001 said:

315/30/18's will clear with a sportline kit. i have seen it in person.

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