The bling factor has influenced most everything about cars it seems, including big wheels that require paper-thin sidewall tires. The practical advantages of the 18, less expensive and broader selection of tires, more wheel protection from potholes, better ride. For experienced drivers on track, the slightly higher sidewall offers more slip angle, so the loss of grip should be just a bit better communicated and easier to handle. IMO, a good rule is to use the smallest wheel that allows sufficient brake clearance with close to OE offset.
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