Rim Shot

Aside from extreme-horsepower super machines, most sports cars offer 16-inch-diameter wheels as the stock size, 17- and 18-inch wheels as sporty upgrades and, in some cases, 19- and even 20-inch wheels as extreme style statements. Usually, wheel/tire width increases with the diameter.

The tradeoffs are inevitable. No matter the wheel diameter, the tire diameter on a particular vehicle stays constant. So with a 16-inch standard wheel, there's a goodly amount of rubber — the tire's sidewall — between the metal wheel rim and the tire's tread. Substitute a 20-inch wheel for the 16-incher, and you end up with a rubber sidewall about as thick as a playing card is wide.

The Sport GT trim on the 2006 Maserati Quattroporte includes gargantuan 20-inch wheels.

The general rule of thumb is that the less sidewall a tire has, the less it flexes and deforms sideways as the car corners hard, which is good for handling and responsiveness. But because it flexes less, the ride is stiffer and less comfortable over bumps. There's simply less shock absorption.

ForbesAutos.com rule of thumb: 16-inch wheels are just fine for a sports car you'll use as a brisk, everyday cruiser; 17-inch wheels are a nice enhancement because they'll accept a wider variety of excellent, high-performance replacement tires when the time comes to buy new tires (and it will come surprisingly soon — see Hidden Costs); 18-inchers are great for hard chargers who can put up with a rougher ride to get every ounce of performance out of their cars; and 19- and 20-inch wheels are for people who think an automobile's running gear ought to resemble that of a stagecoach.

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