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.

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.

• Get the lug nuts or bolts tightened by hand, not with an impact wrench. Follow the torque specs in your car owner's manual or from the wheel maker; recheck torque after the first 100 miles.

Original-equipment tires typically emphasize ride comfort and all-weather grip; plus-sizing reduced both in our tests using a Honda Accord and BMW 5-Series, each with common-model tires. Use the data below and our test results in the color-keyed graphs in What you gain and lose to decide whether the pros outweigh the costs. Plus-size with caution, especially if you drive under varied conditions.

Best for those who want well-rounded performance under a variety of driving conditions.

But factory tires typically compromise optimal cornering grip for all-around versatility.

Best for those who want better handling and cornering without losing much foul-weather grip.

But ride still suffers, and costs for wheels and tires are significant even at this level.

Best for those who value style and dry-weather grip over all-weather performance.

But ride and all-weather grip decline; the risk of damage from potholes and curbs increases.

Best for warm-weather drivers who want even more style and are willing to pay for it.

But you’ll need to be especially careful through puddles; potholes or curbs pose added risks.

Large sport-utility vehicles and pickup trucks allow extra-large plus-size options up to 28 inches in diameter.

We tested a late-model Chevrolet Tahoe SUV with plus-four and plus-eight wheels and tires in line with the extreme sizes typical for trucks. As with our cars, the Tahoe sacrificed ride comfort and snow traction at the large end of the spectrum.

Those are some of the reasons we do not recommend plus-size tires for these mostly all-weather vehicles. Larger, grippier tires could also make some of these trucks tippier by sticking rather than sliding under hard cornering forces and also during emergency road maneuvers--a major reason some auto manufacturers advise owners to stay with the tire size and type the vehicle came with.  

Extreme plus-size truck tires put an even greater strain on brakes, wheel bearings, and suspension parts. The plus-four package we tested weighed 104 pounds more than the originals, while moving up to a 24-inch-diameter, plus-eight package added 152 pounds to the total.

Then there’s the added risk to your back and your wallet: At 92 pounds and $1,360 for each plus-eight wheel and tire we tested, changing even one wheel and tire is likely to be a daunting proposition. And because larger wheels and tires are far more vulnerable to damage, you could wind up parked at the roadside sooner than you think.

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