You’ll find that if you don’t rotate your tires as often as you change your oil, your front two tires will wear out somewhat faster than those on your rear axle. Therefore one of the ways people try to save money on tires is by replacing just two tires at a time. While this may be fine in certain circumstances, it’s always advisable to equip your vehicle with four tires of identical size, model, and manufacture. On staggered fitment vehicles the process is slightly different. The wheels on the back of the vehicle are a different size than those on the front. This is typically done on rear wheel drive cars. Budget limitations may make you hesitant to buy a full set if you, for instance, hit a nail and lose a tire, but there are a few factors to consider that will help clarify your decision.
Mismatched Tires Can Cause Drivetrain Damage
Understand that mismatched tires are a leading cause in drivetrain damage in all-wheel drive vehicles. That is because a new tire without any wear to its tread has a greater circumference than an older tire with its tread worn down. So placing two new tires on the rear axle of your vehicle will cause a discrepancy in how quickly that axel spins versus the front axle with its worn tires. As one axle must spin faster to keep up with the other, stress builds in the drivetrain, which can lead to repair costs that far exceed what you might have saved on tires.
Different Tread Pattern Can Affect Handling & Braking
By similar principle, it is not recommended to have tires of different tread patterns on the front and rear axles of an all-wheel drive or two-wheel drive vehicle. Because your tires’ tread and rubber compound work to maintain grip on the road in various weather conditions, mismatched tires can throw off your vehicle’s performance in handling and braking, even on a perfectly dry road.
How Many Tires Should I Replace?
If your existing set of tires is relatively new, with minimal wear, you may be able to replace just two. It is important to first consult your owner’s manual for the vehicle manufacturer’s recommendation on tire replacement of your all-wheel drive. If no recommendations are found, then the general rule of thumb is the difference in tread depth between the new tires and the ones you’re keeping on the vehicle should not be greater than 3/32nds of an inch, for the reasons already stated. You should also ideally purchase tires identical to the ones being replaced.
The new tires should go on your rear axle, and the tires on your rear axle (presuming they’re in good shape) should move to your front axle. Why do this? Putting tires with greater tread on the front axle may cause you to oversteer, resulting in your rear wheels skidding out, potentially putting you into a spin. But having tires with less tread on the front axle may only cause a loss of traction, such as hydroplaning on a wet road, which can be counteracted by decelerating, not braking or cutting the wheel, and gradually steering to correct any drift as your tires regain traction.
It’s advisable to consult with a tire expert to measure the tread of your tires before replacing only two of them. Measuring by 32nds of an inch requires greater accuracy than you can get with the penny test. Remember the general rule of thumb if the vehicles owner’s manual has no recommendation is, if the discrepancy in tread depth between new and old tires is greater than 3/32nds of an inch, replace all four tires. It isn’t worth the cost or safety risk to do otherwise. And never buy used tires to match your old ones. It’s a circumstance in which you can’t trust what you’re buying.
In all cases, consult your driver’s manual for manufacturer recommendations on tires, rotations, replacements, and other relevant guidelines for your vehicle.