Plus-size tires: When more is less

Larger wheels and tires have taken the fast lane, from street racing to showroom. Tire wheels sized 16- to 18-inch are common place on new vehicles leaving the factory. Older cars still on the road today typically came equipped with 14 and 15 inch tires.

The big-wheeled look has also grown into a significant aftermarket business for tire dealers as drivers increase wheel diameter anywhere from 1 to 8 inches or more beyond the originals—known as plus-sizing.

Style is fueling most of that growth. But retailers also point to more cornering grip and handling. The larger the wheel, the shorter the tire's sidewall and the wider its tread must be to maintain the same outside tire diameter and prevent reducing the tire's load-carrying capacity. The shorter and wider the tire, the better the handling and cornering grip.

Some plus-size wheels and tires live up to their image. Our tests of plus-one, plus-two, and plus-three wheels with common-model tires show that increasing wheel diameter 1 inch—or one plus size—offers the greatest benefit in overall performance. After that, you're likely to pay for small gains in grip and handling with big losses in ride comfort, hydroplaning resistance, and snow traction.

You may also pay more than you bargained for at the counter: Figure on at least $1,000 for four plus-one wheels and tires for a car and $5,000 or more for the largest plus sizes sold for SUVs and pickups.

Plus-sizing brings additional risks for those trucks, since grippier tires that respond more quickly to the steering wheel may increase the chance of a rollover (see Special risks for SUVs below). That's why we don't recommend it for those vehicles unless it's offered as a factory option.

Wheels that fitThe offset between the wheel centerline and mounting area is just one of the specs that determine which wheels and tires fit your vehicle.

Plus-sizing isn't for everyone. If you like the way your vehicle rides and handles, stick with the size and type of tires that came with it.

Will plus-sizing pay off? and the color-keyed graphs in What you gain and lose detail what you're likely to gain and lose as you size up. Here's what to think about if you determine that the style and performance of plus-sizing are worth the compromises and costs:

Consider all the risks. You may not care about snow traction if you live in the Sunbelt and drive mostly on dry roads. That's where the wider footprint and stiffer, shorter sidewalls of large plus-size tires perform best. But driving through puddles is more treacherous wherever you live. That's a compelling reason to choose the plus size closest to the original wheel and tire size, which offers the most performance gain with the fewest sacrifices.

Increased risk of damage from potholes and curbs is another consideration. Besides compromising ride, shorter sidewalls provide less cushioning for wheels and tires. Our pothole test bent the plus-two and plus-three wheels on our BMW 5-Series and damaged the wheel and tire on our plus-two-equipped Honda Accord.

Get the right tire size. A car or tire dealer can tell you the proper plus sizes for your car based on its original tire size.

A rule of thumb: Increase tire width by 10 millimeters and decrease sidewall height by 5 to 10 percent for each 1-inch increase in wheel diameter. And make sure speed and load rating of new tires is at least as high as on the factory originals.

Also check the recommended inflation pressure when switching between a P-metric tire and Euro-metric tire size designation, since doing so may require a pressure change to maintain your tires' load-carrying capacity. Guidelines vary among tire manufacturers, so it’s best to stay with the same size designation if possible. Tire makers' recommended pressures may vary from those auto makers suggest.

Check the wheels. Most plus-size wheels are aluminum or some composite. Quality varies widely. Fordged wheels are more expensive, but tend to be stronger than some cast alloy wheels.

Make sure that plus-size wheels were made specifically to fit your vehicle. They should have the right lug-nut pattern so that the holes line up precisely with the holes or threaded studs on your vehicle. While some “universal fit” wheels are made for several vehicles, they can put added stress on the lug nuts or bolts and come loose while driving. Some wheels also need special nuts or bolts.

Another wheel caveat involves offset—the distance between the wheel's hub-mounting surface and centerline, as shown in the image above. Have the retailer confirm that plus-size wheels have the correct offset for your vehicle. And be wary of spacers, which retailers often sell as a way to make wheels fit by moving them out from the hub.

Try to buy tires and wheels as a set. Local tire stores and mail-order retailers often sell wheel-and-tire packages with the tires mounted and wheels balanced. Packages are an easy way to choose wheels and tires that fit your vehicle.

Wherever you buy wheels and tires:

• Use an installer experienced with plus-sizing, especially if the retailer mounts the tires and wheels. Inexperienced shops could damage both during installation.

• Get a return guarantee that covers damage, and includes shipping if you buy by mail, if the plus-size wheels and tires the store suggests rubs against the wheel wells or changes speedometer readings.

• Have suspension parts serviced, if needed, and wheels aligned to prevent the new tires from wearing prematurely.