How to Buy Tires

Before you buy new tires

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:

• Standard all-season tires are best for most drivers. These tires offer overall good traction (especially in dry conditions), long tread wear and a comfortable ride at a reasonable price. They lack the precise handling and grip of performance all-season tires. Tread wear is between 40,000 and 100,000 miles, and wheel sizes generally range from 14 to 18 inches, with T and H speed ratings.

• High-performance all-season tires are best for those who want better handling and grip without giving up too much comfort and wear. Tread wear is 40,000 to 70,000 miles, and these tires are appropriate for wheel sizes from 15 to 20 inches. They carry speed ratings of H and V.

• Ultra-high-performance tires are for those who want the best wet and dry braking and handling at the expense of tread life. Summer tires are not appropriate for snow or ice. Most models have no tread-wear warranty at all, although our Best Reviewed Michelin Pilot Super Sport (*Est. $195) is covered for 30,000 miles. Wheel sizes range from 15 to 22 inches, with W, Y and Z speed ratings.

• Match new tire specifications to those of your existing tire. You'll need a tire that fits your existing wheels and has an adequate load rating for your vehicle. You'll find these specifications on your existing original tires or in your vehicle's manual.

• Proper inflation is critical. No tire will perform up to its capabilities if the proper level of inflation isn't maintained. To be sure that your tires are inflated to the correct levels, check your tire pressure monthly. Doing so will not only help ensure that your car performs properly, it will also help you achieve the best possible fuel economy. We discuss the benefits of monthly tire pressure checks in a blog post on how to choose the best tire gauge.

Understanding tire sizes and speed ratings

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.

Be cautious when considering plus-sizing

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:

• The wider a tire gets, the more likely it is to float -- not bite -- on wet or snowy roads.

• The shorter the sidewall, the less cushioning between the wheel and the road. In pothole tests, Plus Two and Plus Three tires damaged the wheels on a BMW 5-Series and a Honda Accord.

• Pickups and SUVs are more prone to rollover than other vehicles. "Grippier tires that respond more quickly to the steering wheel may increase the chance of a rollover," ConsumerReports.org says. Editors don't recommend plus-sizing for pickups or SUVs unless it's a factory option.

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.