AWD / 4WD Replacing 1, 2 or 4 Tires
Jan 6, 2023
Replacing just one or two tires on an AWD vehicle could cause unnecessary wear and tear on your drivetrain, or confuse the traction control system to think that you are frequently losing traction. A new tire is larger in diameter than one of the same brand, type and size that’s part way through its tread life. In fact, studies have shown that differences of just 2/32 of an inch in tire tread between tires on the same vehicle can impact vehicle performance. For example, if you were to replace just two tires on your AWD or 4WD vehicle, you would have a slightly larger diameter on the new tires, due to deeper tread. A small difference in the front and back tire diameter means the two axles are always turning at different speeds, even if the car is going straight down a highway. This is contrary to how the vehicle was designed to operate and will likely lead to early malfunction.
Mismatched Tires on AWD Vehicles May Cause Damage
Four-wheel drive and all-wheel drive vehicles are equipped with additional differentials and/or viscous couplings that are designed to allow momentary differences in wheel speeds when the vehicle turns a corner or temporarily spins a tire. However, if the differentials or viscous couplings are forced to operate 100% of the time because of mismatched tires, they will experience excessive heat and unwarranted wear until they fail.
The drivetrain is the system that transfers power from the engine to the wheels. By having different size tires, even when they are labeled the same size, they are putting more stress on the drivetrain which will eventually cause problems to the system and your AWD vehicle.
Ideally, whether your vehicle is AWD or has a conventional drive system, you should have all four tires replaced so that they are all the same size with the same amount of traction. This is the best way to go so that you are not damaging your drivetrain or any other parts of your vehicle.
Tread Depth & Circumference
By only replacing one or two tires on your vehicle, you could be causing damage to your drivetrain. As tires are used and driven on, the tread life of that tire is diminished. This makes the tire diameter smaller than a new tire. By replacing one tire, it forces the other tires to spin slightly faster to keep up with the new one. Due to the increased diameter of the new one, a single revolution of the tire will travel farther than the older tires.
As an example of different tire diameters resulting from tires of different tread depths, we’ll compare two 225/45R17-sized tires, a new tire with its original tread depth of 10/32-inch and a second tire worn to 8/32-inch of remaining tread depth. The new 225/45R17-sized tire has a calculated diameter of 24.97″, a circumference of 78.44″ and will roll 835 times each mile. The same tire worn to 8/32-inch of remaining tread depth is calculated to be 1/8″ shorter with a diameter of 24.84″, have a circumference of 78.04″ and will roll 839 times per mile. While the difference of 1/8″ in overall diameter doesn’t seem excessive, the resulting 4 revolutions per mile difference can place a continuous strain on the tires and vehicle’s driveline. Obviously, the greater the difference in the tires’ circumferences, the greater the resulting strain.
Replacing Pairs or Individual Tires
There are several suggestions that have been offered to drivers who are replacing pairs or individual tires on their four-wheel drive and all-wheel drive vehicles. Some vehicle manufacturers recommend that all tires maintain the same rolling radius and circumference, while others suggest that all tire circumferences remain within 1/4- to 1/2-inch of each other. Other vehicle manufacturers recommend that all four tires remain within 2/32-, 3/32- or 4/32-inch of each other, or within 30% of each other in relative remaining tread depth.
Regardless of the vehicle manufacturer’s recommendations, the least stressful application is when all four tires are the same tire brand, tread design and equivalent tread depth.
Before buying pairs or individual tires for all-wheel drive and four-wheel drive vehicles, drivers should read their vehicle’s owners manual or contact the dealer’s service department for confirmation of their specific vehicle’s requirements. (Photo: Transfer case damage due to running different tire sizes for an extended period of time.)