So, you need to replace a flat tire that cannot be repaired. That’s bad enough. But then the repair guy says that you really should replace all four of your tires. Do you really need to replace three tires that seem perfectly good, just because one bit the dust? In many cases there are several good reasons why you should replace all four tires, instead of just the one that went flat.
The reason most all-wheel drive vehicles manufacturers recommend that you replace all four tires at a time is because all four wheels should have the same rolling circumference. If the wheels are not uniform, abnormal drivetrain wear can occur, resulting in costly problems down the road.
All-wheel-drive systems are designed so that the differential and the computer work together to send the right amount of torque to each wheel to minimize slippage and maximize control. When one of the tires is a different size than the others because three tires are worn and one is brand new, the computer will take an inaccurate reading and the differential will have to work excessively hard. This can eventually result in damage to the drivetrain.
Unless your tires are brand new, the wear on all of your tires means you should probably bite the bullet and buy a new set. Additional benefits you’ll gain with a full set of tires for replacement include a more comfortable ride and better safety. Uneven tires can result in road noise and a vehicle that handles improperly, affecting maneuverability, traction, and smoothness of the ride.