increased weight of larger wheels, more prone to pothole damage, degraded ride quality, but
damn they look better. :-)
__________________ John P. (TT 225)
2011 S5 Coupe Quartz/Magma/Sport Diff/Carbon/B&O/6-Speed Manual
• A.W.E. Tuning Exhaust
• H&R Street Coilovers
• Vossen CV3 20"x10.5" x 4 (first in the U.S. on all four corners)
• Dipstick mod
• Clear bra
-2001 Audi TT quattro (Deposit placed in 1998; Car sold in 2008)
I can't think of a single advantage other than looks if you like a larger wheel
As John pointed out in almost all instances an 18" wheel will weigh more than a 17". The sidewalls will be shorter with a resulant stiffer/harsher ride. The costs are always higher, many shops might not be able to install 18" tires when you need new tires.
The diameter of the wheel has nothing to do with clearing larger brakes, only larger rotors. The calipers can have clearance issues with a 19 and 20" wheel, it is all about inner wheel curvature and the wheel offset.
The gap between the fender arch and the top of the tire will remain the same no matter what size wheels you use, the perception will only appear to be great with a larger diameter wheel because the tire sidewall is shorter. This is all based on you getting the correctly sized tire to keep your speedo accurate.
Less tire wall deflection is only plus...negatives are covered below.
A profile that short on the street not only makes the ride racecar hard but increases likely hood of rim and tire damage on public roads. 18s that work on street were designed that way from ground up with higher profile tire incorporated in orginal design.