If you have an All Wheel Drive (AWD), part time Four Wheel Drive (4WD) or a Full Time 4WD (FT-4WD) vehicle, you may find yourself saying this when you want to buy less then four tires.
Let’s just say it… if you have an AWD or FT-4WD vehicle, replacing one tire is almost never an option. If you drive a part-time 4WD vehicle it is recommended that you replace your tires in pairs. On AWD and FT-FWD vehicle, you may need to change all four tires (even if only one tire has gone bad). With AWD and FT-4WD vehicles, replacing less than 4 tires can be harmful to your vehicle’s drive-train. This is why many AWD/FT-4WD vehicle manufacturers state that all 4 tires need to be replaced at the same time.
Let’s discuss this. When you bought your AWD/4WD vehicle, you bought a vehicle that is engineered with some of the latest safety and technological features. These features help you keep control of your vehicle even when one or more of your tires lose traction. Your vehicle has a specialized drive-train or drive-line (which contains differentials, a transfer case, specialized gears, and drive shafts), and these components can allow each of your tires to spin at different speeds from each another. Some vehicles can have all four tires spinning at different speeds! This feature helps the tires to keep traction in slick or muddy environments. The specialized drive-line components are only designed to allow momentary differences in wheel rotation speeds when a vehicle turns a corner or temporarily spins a tire. In order for this system to work properly, all the tires must be the same tread pattern, the same tread depth, and from the same tire manufacturer. If the tires have different tread patterns, manufacturers, or tread depths, the differentials (and other related components) will be forced to work 100% of the time -- which they are not designed to do. This will cause excessive heat and unwarranted wear on the drive-line components until they fail.
When replacing tires on AWD and FT-4WD vehicles, the tires must always be the same size, model, and tread design. When replacing less then four tires, the remaining tire life must be measured to see if the remaining tread depths are sufficient for the AWD/FT-4WD system to function properly. Replacing one or three tires is not an option unless you are utilizing a full size spare of the exact size, manufacturer, model, and tread depth of the new tires you plan to install. Otherwise, you’ll need to change 2 or 4. Some vehicles allow for the replacement of two tires if certain criteria is met. For example, some AWD/4WD vehicle manufacturers specify that you can replace 2 tires if the other tires are within 2/32 of an inch from the new tires. This translates to a tread depth within 20% of most new tires. (Most new tires start with 10/32’s of an inch.)
Here are some examples of vehicle manufacturer’s recommendations. One owners manual states that the “rolling radius of all 4 tires must remain the same”, or within 4/32-inch of each other in remaining tread depth. Another recommends that tires should be within 30% of each other. And yet another states; on AWD vehicles, all four tires need to be within ¼ inch of tire circumference or about 2/32-inch of each other in remaining tread depth.
The best place to search for tire replacement guidelines is in your vehicle’s owner’s manual. Here at Lex Brodie’s we recommend referring to your owner’s manual when replacing tires on your AWD/4WD vehicle. If the manual does not state the proper way to replace tires we will recommend no less than 2 tires (only an option when the remaining tires are with in 2/32nd of the new tires tread depth). This will ensure that the drive-line is undamaged, and also help keep you safe.