One of the defining features of an all-wheel drive car is its unique ability to divide the horsepower produced by the engine between each of the vehicle's wheels. On loose, slippery or snow-covered surfaces, this feature is especially useful as the car is much less likely to lose control. To accomplish this, all of the car's wheels are connected mechanically through special drivetrain differentials that temporarily allow the wheels to spin at different speeds while cornering or encountering instability such as on snow, ice or sand. The downside of this is that the tires on an all-wheel drive car must be properly matched and worn evenly. Otherwise, the differentials must function continuously to adjust to the mismatch, causing undue wear and tear on the tires.
All-Wheel Drive Tire Requirements
With an all-wheel drive vehicle, it's important that each of the tires match in terms of size, tread design, tread depth, manufacturer and inflation pressure. Using tires that match completely helps to reduce overall strain. As the differentials cause the tires on an all-wheel drive vehicle to rotate irregularly relative to each other, mismatches can lead to tires with differing circumferences. When the circumference between 2 or more tires does not match, one tire will experience more revolutions per mile. This leads to excessive and unnecessary strain on the vehicle's drivetrain. At worst, parts of the drivetrain may break down as a result of even the smallest mismatch.
How to Avoid Problems
The best way to avoid experiencing any problems with mismatched or unevenly-worn tires is to prevent these issues before they ever arise. Start by having the vehicle's tires rotated at regular intervals. While cornering, accelerating and braking, each of car's tires are put through different levels of stress. Tire rotation helps to even out the wear and tear, so no one tire experiences an excessive amount of strain. Not only will tire rotation get the most mileage out of the tires, it will greatly reduce the likelihood of damage to any of the drivetrain components.
It's a given than tire sizes should always match on all-wheel drive vehicles. Tread depth and tread design should always match, and it's imperative that the same brand of tire be used when replacing one or more. The reason being is that different manufacturers produce tires that vary both in terms of tread design and depth, although the size specifications may match perfectly. Even the slightest variation can cause problems.
If tire replacement is in order due to a blowout, accident or other reason, it is not necessary to replace all 4 tires on an all-wheel drive vehicle. Chances are, the remaining 3 tires have life in them yet. In order to avoid unnecessary strain on the drivetrain and to save yourself the expense of total replacement, it's possible to shave tread off of the new tire. This process uses a special tire lathe to match the circumference of the new tire with the 3 older tires. Tire shaving results in matching tread depths, equal circumferences and a stable drivetrain. While the new tire may lose some mileage life, the net effect will be positive.