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.