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It is recommended to replace your tires in sets of four for all vehicles, but it is particularly important for all-wheel drive vehicles. All four tires should be the same size, brand, tread design, construction, and tread depth to prevent differences in the outside diameter of each tire. Even slight differences in the outside diameter may cause drivetrain damage or mechanical malfunction

Two Reasons to Replace All Tires at Once

1. Mismatching AWD Tires Can Damage Your Vehicle

Front tires on an all-wheel drive (AWD) vehicle often wear more quickly than those on the rear axle. It can be tempting to only replace the two front tires, but a new tire is larger than one of the same brand, type, and size that’s partway through its tread life.

  • A difference in diameter of less than half an inch between front and rear tires on your AWD can mean trouble for the drivetrain, or the parts of the car that transfer the power to move the vehicle forward.
  • If the two tires on one axle are spinning faster than the others, your car’s electronics may think those are slipping, and put you in the wrong gear. Most AWD systems in today’s cars include sensors on each wheel that monitor traction and wheel speed hundreds of times per second. This is what allows the AWD system to work in slick conditions, by sending power to whatever wheel(s) have the most traction.
  • When smaller tires are spinning faster, the system may put your vehicle into four-wheel lock, the gear that’s used for driving in slippery conditions.

2. Transfer Case Problems

  • In vehicles equipped with all-wheel drive (AWD) systems, the transfer case (gears that transfer power from the transmission to both the front and rear axles) and the car’s internal computer work together to send power out to each wheel. The amount of power-per-wheel can vary, depending on each wheel’s individual work load. For example, in a straight line each wheel carries a reasonably similar load. In a cornering situation, the stress on each wheel is very different.
  • The amount of power the internal computer sends to each wheel—based on what your AWD vehicle needs to go down the road—helps to manage how hard the transmission and transfer case are working. Inconsistent outside diameters caused by different tire sizes, tread patterns, or tread depths can force an AWD computer’s readings to fluctuate, and various wheels will receive inefficient or incorrect power loads. As a result, the drivetrain (computer, transmission and transfer case) must constantly readjust, doing more work than necessary and eventually, may break down.

While replacing your tires in sets of fours will greatly reduce your risk of problems, regularly rotating your tires and keeping them properly inflated will ensure your new tires wear evenly. Even tread wear is key to keeping your all-wheel drive system operating at its best. Check out our Tire Buying Guide to discover which treads best match your driving needs