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The conventional wisdom among drivers of all-wheel-drive vehicles has been that when they need to replace a single tire, every tire should be replaced. Doing that ensures that the AWD system won't experience unbalanced wear and that there's balanced traction at all four corners.
This approach may work when it's naturally time to replace four worn tires, but it can be costly when just one tire goes flat or is damaged. There's a clever solution that protects the car and lets owners avoid buying tires by the set: shaved tires.
What's the Problem?
A tire's circumference gets smaller as the tread wears and the amount of rubber decreases. As a result, a worn tire rotates faster than a new one. For example, Subaru warns owners that mismatched tire circumferences can cause serious mechanical damage to a car's all-wheel-drive system. Drivers with an AWD vehicle should refer to their car’s owner’s manual for specific guidance on tire replacement.
It's always best to use four tires from the same brand—and the same model—on a vehicle. Unless specified by the automaker, tires should be the same size, and have the same speed rating and load index. (See our tire buying guide to learn how to read a tire.) Refer to the tire information placard usually found on the driver’s doorjamb for the appropriate tire size and recommended inflation pressure.
Buying four new tires may be needlessly expensive for drivers who only need a single tire to join the three other moderately worn tires. But you can buy a single new tire from TireRack.com and have the company shave it to the tread depth that matches the depth of your other tires. It will shave any tire you buy from the company, usually for $25 to $30. (Call TireRack customer service at 888-981-3953 for more details.)
This service is relatively inexpensive compared with the alternative: buying four new tires.
Note that shaving a tire will likely nullify its tread-wear warranty. Other retailers may offer a similar service, though the special equipment to shave a tire’s tread isn’t common.
How Worn Is Too Worn to Shave a Tire?
A typical new all-season tire will have a tread depth of about 10/32” and is worn out at 2/32”. So shaving a replacement tire makes the most sense if the remaining tread on your tires is no more than about half-worn, at approximately 6/32”.
Drivers interested in this strategy should buy a tread-depth gauge (readily available at auto-parts stores). They can measure the tread depth of each tire in the grooves that have tread-wear indicators, which are raised platforms set 2/32” high that appear flush with the tread to indicate that a tire is worn out.
If the wear seems inconsistent between tires or there's evidence of uneven wear, such as one groove wearing faster than another, then it would be better to buy four new tires and have the car checked out for suspension or alignment problems.
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