Where to Install a Pair of New Tires?
Ideally, it is best to replace all four tires at once so that every tire’s size and profile matches one another. This will provide the most consistent performance while ensuring maximum safety. However, it’s not always the most economical to replace all four tires, especially when perhaps only two tires are worn and the other two tires still have good tread depth.
No matter if your car is FWD, RWD, or AWD/4WD, it is recommended to install a pair of brand new tires on the rear axle of the vehicle. Virtually all tire manufacturers will recommend doing this because it is the safest way to install two tires on a vehicle. To minimize any liability, these companies will always recommend going about it the safest way possible: installing the new tires on the rear axle.
Why Install on the Rear?
The assumption here is that the new tires installed on the vehicle will be able to provide more traction with the road under most circumstances. These tires will grip the road much better than the existing tires already on the car. This matters when the car is making a turn and you lose traction (e.g. rain, sand/mud on the road, etc). Because the new tires will have more tread than the existing two tires on the other axle, it will be less likely to hydroplane or lose grip than the other tires.
Essentially, the two new tires grip the road well while the two existing tires don’t. This lost of traction of the two used tires will cause the car to slide in different ways. Imagine there is a wet road and a car is going around a curved road. Here are two scenarios of a car losing traction, one with new tires on the front axle, and the other with new tires on the rear axle.
New tires on the front axle
Front tires keep grip, rear tires lose grip so rear end starts coming around and you lose control in a spinout (oversteer condition)
New tires on the rear axle
Rear tires keep grip, front tires lose grip so you can no longer steer and the car continues its line off the road (understeer condition)
In both cases, you certainly may lose grip and consequently lose control of the vehicle. But, an oversteer condition is generally a more dangerous case than an understeer condition. This is because with oversteer, the car spins which tends to be more difficult for the general public to control. With understeer, the car continues going straight instead of driving through the turn which is a more controllable situation for the everyday driver. Therefore, it is generally safer to install new pair of tires on the rear axle and keeping the existing worn tires on the front axle.