Can I Just Replace One Tire When It Goes Flat?

What Shoppers Should Know

• It’s rarely a good idea to replace just one tire with a new one.
• There are other options besides replacing all four tires.
• Uneven tire diameters can throw off the anti-skid system and even cause undue wear.

While it’s tempting to buy just one new tire to replace one that has gone bad, it’s almost never a good idea. Only if the others have little wear and you’re buying an identical tire is it advisable to mount only one new tire on your car.

That’s largely because your car’s electronic stability control — a valuable dynamic safety feature — relies on wheel-speed sensors to determine wheel speed, which is then used to make adjustments to keep the car stable. A new tire would have deeper tread,and thus a larger circumference, that would make it spin more slowly than a worn tire to cover the same distance. That difference could confuse the antilock brake system.

Related: How Do I Find and Stop a Slow Tire Leak?

On all-wheel-drive vehicles, it may be even more important that all tires have close to the same amount of tread and thus be the same circumference. That’s largely because many AWD systems include mechanical components that can wear out if they have to compensate for different tire rotation speeds. This also makes tire rotations more important.

Some Notes on Tread Depth

A tire’s tread depth is typically measured by 1/32 of an inch. New passenger-vehicle tires usually start with about 9/32 to 12/32 of an inch of tread. They’re commonly considered “worn out” when the tread is down to 2/32.

Although it’s not ideal, some experts say you can get away with putting just one new tire on a car if the others are at 70% of the new tire’s tread depth. So, if the new tire starts with 10/32 of tread and the old tires all have at least 7/32, you’d probably be OK. However, as mentioned above, that probably doesn’t apply if your vehicle has AWD. Check your owner’s manual under “Tires” for any guidance pertaining to replacing tires to be sure.

For the safest performance, you should also have all tires be not only of the same size, but also the same brand and model. They should also be the same type (i.e., don’t mix all-season and summer tires). This is so they all provide the same level of traction, as different brands and different types of tires can have different levels of grip.

Alternatives to Buying Four New Tires

While the tire dealer may suggest you buy four new tires when one goes bad — and that’s ideal — it’s not very cost-effective and may not be entirely necessary.

If your vehicle is either front- or rear-wheel drive and the tires have at least half their life left, you might consider buying just two new tires.

In that case, the two new ones should go on the rear of the car. This might seem counterintuitive, as the front tires typically carry more weight and have to do the steering, the combination usually making them wear faster. But putting the new tires in the rear reduces the chance that they’ll hydroplane over standing water (meaning the tire starts riding on a film of water, thus losing contact with the pavement). If that occurs, the back of the car loses traction, which can cause the car to lose its directional stability and thus spin.

Also, some tire shops have the capability of shaving some tread off a new tire to get it closer to the tread depth of the older ones. This will cost some money, so balance that against applying the charge to buying a second tire. However, if your car has AWD, this may be a more attractive option than buying four new tires.

Some tire shops also sell used tires. Often these are the three good ones left after someone decided to buy four new tires when one went bad. The trick is finding one of the same size as your others … of the same brand and model … and with close to the tread depth you need.

Relatively few vehicles today have a full-size spare tire, but if yours does, you might use that one in combination with one new tire to make a pair — using your other old tire as the spare. This will require extra charges for mounting, dismounting and balancing tires, but it may work out to your advantage.

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Why a Flat Tire Might Not Be Repairable

Many flat tires can be repaired with either a plug or a patch. However, any cut, hole or bulge in the sidewall of the tire can’t be repaired, and some tire shops won’t repair a hole that’s in the outer edges of the tread or if the tread is worn down too far. The hole could also be too large. Regardless, you’re pretty much at the mercy of the tire dealer’s judgement.

Some shops also won’t repair run-flat tires. That can be a real problem, as they may not keep many (or any) new run-flat tires in stock. In that event, you may be forced to replace a damaged run-flat tire with a regular tire of the same size — on a temporary basis, critically — until you can get to a shop that has or can order the proper run-flat tires. Note that some cars fitted from the factory with run-flat tires don’t have any spare tire at all, so if your new “regular” tire goes flat, you’re stuck. That’s a good reason why this should only be considered a temporary, emergency solution.

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