Most people remember the myths of years past that claimed you had to replace the tires two at a time or replace all four at once. In the past, snow tires used to be mounted on the drive wheels for winter usage, and you wanted to mount two at a time to ensure that the wheels that helped you gain traction (either the two in the front or the two in the rear) were both of the same tread and brand.
However, you can safely replace just one tire as long as the others still have plenty of tread. Most technicians and mechanics do recommend that you have four matching tires that are the same model, same type, and have the same degree of wear. The reason is that when the tires match, they behave the same way. Whether you are braking, taking a corner, or accelerating, all four tires are predictable and balanced. If the balance is off even slightly, you are likely to notice changes in traction and performance.
What is the Tread Depth?
Tread depths are always measured in 32nds of an inch, which can be confusing for average drivers. To get a better idea, most new tires have between 12/32 and 10/32 inches of tread or about 5/16ths to 3/8ths of tread. If you buy one new tire and the other tires have only lost up to 4/32 their original depth, you can probably replace the damaged tire and have no issues. However, if the other tires have lost more than 4/32 inches of tread, it may be wise to replace all the tires when you replace one that is damaged.
Why AWD Is Different
Along with that, some exceptions prove the rule. Many all-wheel-drive vehicle manufacturers recommend that you replace all four of the tires at once regardless of how much tread is left. They reason that the new tire is bound to have a larger diameter than the others. Therefore, even if the others have only lost a few 32nds of their depth, they can spin faster than your new tire. That minuscule difference can cause your AWD system to try to engage itself on dry pavement, which could damage the system.
With an AWD vehicle or a traditional four-wheel-drive car, all four of the tires should ideally be replaced together so that they all have the same traction amount and diameter.
What about Front- and Rear-Wheel-Vehicles?
Similar guidelines may also apply to front- and rear-wheel-drive vehicles. If half the tread on all four of the tires is gone, you shouldn’t replace just one of the tires because it results in one wheel that spins slower than the others, which can send false signals to your antilock braking system and traction control system. It can also result in one tire that has more/less traction for braking, accelerating, or cornering, which might affect the car’s behavior.
Regardless of whether the car is a rear-wheel or front-wheel-drive vehicle, it is better to replace the pair of tires that reside on the same axle. However, you should consider replacing all four tires if the tread on the current tires is worn significantly.
Why Shaving Isn’t Suitable
Many repair shops can ‘shave’ the new tire so that it has a matching depth with the other tires. Some dealerships can also shave off the tread depth using a special machine. However, most manufacturers and mechanics do not recommend this method.
If you do choose to replace one tire only, your replacement should have the same tread pattern, size, and model number as the other tires. If necessary, you might consider having the new tire shaved to prevent excess wear and keep everything balanced.