To be totally honest with you, 18's will look way too small in that style of wheel. The cross spokes tend to make a wheel appear a little smaller as does the larger rim. An 18" spoked wheel like the Style 69's look a little bigger than 18" simply because of the design.

There was a thread a while back by Steved who fitted a set of 19" M3 CSL wheels on his 4.8is and they didn't fill the wheel well enough. Find that thread! EDIT: Found it! As you can see, it looks odd and those are 19's. Sure some bigger tires would help but it would still look unbalanced.

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