Here's a brief primer to help you determine what to look for and evaluate your options.
Typically, the larger the wheel, the shorter and wider the tire. Aspect ratio (the tire height compared with the tire width) affects handling, traction and ride comfort. A lower aspect-ratio number improves handling and traction on dry roads at the expense of ride smoothness, gas mileage and wet-road handling. A higher aspect ratio number, on the other hand, will improve your ride smoothness.
Deciphering Sidewall Speak
The numbers are pretty easy to understand once you know the manufacturer's code. The first number is the tire width in millimeters from sidewall to sidewall. The number after the slash is the aspect ratio: In this case, the height is about 65 percent of the width. The next letter, either "R" or "B," indicates tire construction: "R" means radial; "B" means bias ply. The next two digits show the wheel diameter – in this case, 16 in.
Following a space will be two or three digits that describe load index, a range that indicates how much weight the tire is certified to carry at maximum inflation pressure -- in this example, "98" indicates a maximum load of 1,653 pounds. The next letter (H or Q through Z) represents the speed rating – in our example, the "T" means that the tire is rated up to 118 mph. (Speed-rating and load-rating charts are available on most tire manufacturers' Web sites.) Finally, some tire codes may include one extra designation: "M&S," meaning the tire is rated for mud and snow.
Try to rank performance (traction and handling), comfort (ride smoothness) and budget (tread life, season-specific and gas mileage) in priority order. Performance tires grip the road better but produce a rougher ride. Look for AA- or A-rated tires for the best wet-stopping performance. Touring tires provide smooth rides on highways. Summer tires are for temperate climates. The newest energy-conserving tires designed for hybrids boost mileage by reducing friction.
Drivers in snowy regions must decide whether to buy all-season tires for year-round use or to invest in two sets of wheels and tires (snow tires on steel wheels for winter and three-season tires on alloy wheels for the rest of the year). Dedicated snow tires such as the Bridgestone Blizzak combine softer rubber that stays flexible in cold weather with aggressive tread patterns designed to grip snow. They are superior to all-season tires in deep snow but are less suited to driving in heavy rain.
Sipes: Small slits add traction in icy and light-snow conditions
Grooves: Channel water away
Blocks: Provide primary traction
Ribs: Provide a continuous-contact band
Dimples: Improve tire cooling
Shoulder: Provides continuous contact with the road while turning
Tread-life rating is one of the key ways tire makers encourage us to spend more and to choose their tires over competitors'. Predicted wear mileage generally rises with price. This is a decent way to compare durability within a brand, but it is less helpful when deciding between brands. Tire manufacturers do their own wear tests on a standard 7,200-mile course but are free to forecast long-term durability based on their own interpretations of the data. Discount brands' projections may be more optimistic than realistic.
Tread Wear Warning Signs
One-side tread wear: Tires that show excessive wear on one side are often an indication of a misaligned front end or worn steering components.
Even tread wear: Ideally, if your tires have been appropriately inflated and rotated and the car is properly aligned, your tires will have even tread wear.
Outer-edge tread wear: When the tires show excessive wear on both the inside and outside edges, it is often a signal that the tires have been used with the pressure too low.
Center tread wear: High tire pressure will make the center of the tire tread wear excessively; this also reduces the contact surface with the road and reduces traction.
When comparing prices, be sure to find out what's included. Fees vary for mounting, balancing, valve stems, Tire Pressure Monitoring System (TPMS) servicing and disposal fees. Also check the freshness dates to confirm that the tires are no more than a couple of years old. Rubber dries out and hardens as it ages; the younger the tire you install, the longer it will last. Independent tire dealers carry the broadest selection. Online retailers are great for comparing test results, surveys and consumer reviews on specific brands and models.
Follow these practices for tire safety, durability and fuel efficiency: