Replacing four tires
If you begin with four new tires, they should all grow old together. So ideally, every so often you would buy a whole new set of four tires. That’s the best scenario and a very common scenario as well. But that’s not always the way things go. Sometimes one or two tires wear out long before the others. The main reason this happens is because owners forgot to rotate their tires. When your tires stay on the same wheels, they wear unevenly. We’ve written more extensively on this matter. Simply put, depending on your car, different tires will carry different weights and stresses. As a result, they will wear at different rates and in different areas. The simple solution is performing consistent rotations every oil change. But there are other causes of premature tire failure, including a bad tire, tire damage, driving on a flat tire, etc.
Replacing two tires
If two out of your four tires still have a lot of life left, only replacing the two older tires is a real possibility. The key is to make sure that the two new tires and the two remaining tires have tread depths within 4/32 inches of each other.
If you go this route, you should install the two new tires on the rear and place the worn tires on the front. This is because the front tires usually bear more weight because of the engine, and they always have more control because they’re attached to the steering wheel. This naturally gives the front tires more traction whenever you’re driving in slippery conditions. And for the same reasons, most experts agree that it’s easier to control a front-tire blowout than a rear-tire blowout. So it’s best to keep your best tires on the back.
There is one thing to consider before buying just two tires. Once you have mismatched tires, it becomes harder to rotate or ever get back into four evenly worn tires.
Replacing one tire
It is generally not a good idea to only replace one tire at a time. While there is some room for variance in the size of the front and rear tires, there is much less wiggle room allowed in side by side tires. This is because side-by-side variation can destabilize the car as well as cause problems like premature drive-train failure.
If one of your tires has been damaged, but the other three are fine, then we recommend replacing two tires. This way you only purchase one “extra” tire. But if you’re set on just replacing the damaged tire, it may be worth looking into a used tire shop. You will need to get a single new tire that matches, as close as possible, the diameter, tread depth and tread design of its counterpart. However, know that there are implicit dangers in going this route. It is always better to have an exact match for your side-by-side tires.