First, experts say you must understand the kind of tire you need. Regular and high-performance all-season tires will satisfy the largest percentage of consumers, but models for SUVs and other trucks are different than those for cars and minivans. Ultra-high-performance summer tires are appropriate only if you're willing to sacrifice all-weather versatility, tread life and price to improve your car's acceleration and handling.
Choose a tire type and size to suit your vehicle and driving conditions:
Tire sizes are represented by a ratio followed by a whole number. The ratio comprises the width in millimeters from sidewall to sidewall and the percentage of that width that makes up the profile (the distance between the rim and the outer edge of the tire); the whole number is the rim diameter in inches. A tire with a size of 215/60-16 is 215 mm wide, 129 mm (60 percent of 215) from the ground to the rim and is intended for a 16-inch wheel.
Tire manufacturers use letters to represent the maximum speed at which a tire should be driven. There are about 20 different speed ratings, but the most common are Q (up to 99 mph), S (up to 112 mph), T (up to 118 mph), H (up to 130 mph), V (up to 149 mph) and Z (149 mph and above). Some Z-rated tires have an extra rating to show that they can handle even faster speeds: W (up to 168 mph) or Y (up to 186 mph). Experts say that even if you have no intention of driving at speeds of 130 mph or more, tires with a high speed rating are also better performers at more mundane speeds. While snow tires and most all-season tires perform well with Q, S or T speed ratings, performance tires should have at least an H speed rating.
An ongoing trend for car owners is to plus-size tires and wheels. Drivers buy larger wheels and shorter, wider tires. For example, if your car specifies a wheel size of 16 inches, increasing wheel size by one inch would result in a 17-inch wheel or Plus One for your vehicle. The tire you buy will then need to have a shorter sidewall, and usually a wider tread, to accommodate the same load and tire diameter.
Although many drivers are doing this for cosmetic reasons -- a larger wheel and narrower tire has a sportier look -- some experts say you can gain traction and handling by plus-sizing, because a wider tire can get a better grip. However, ConsumerReports.org says Plus One gains you the most benefit at the lowest price. Increasingly larger Plus Two or Plus Three wheels and wider tires cost exponentially more and offer smaller performance gain over Plus One. They also add some risks, ConsumerReports.org says:
There are many considerations that will factor into a decision to plus-size. First, your car must be able to accommodate the additional offset of a wider tire. "Be wary of spacers, which retailers often sell as a way to make wheels fit by moving them out from the hub," ConsumerReports.org says. Also, you must be sure that the tire's load rating is at least the same as your factory-specified tire; the tire may require a pressure change to achieve that. The new wheels should be made specifically to fit your vehicle to prevent strain on the lug nuts and bolts. Experts advise buying from a dealer/installer with experience in plus-sizing who can identify the appropriate size options for your car.