Mixing Tires(Lea en español)
As a general rule, tires should not be mixed on any vehicle unless specified as acceptable by the tire or vehicle manufacturer. Drivers should avoid mixing tires with different tread patterns, internal constructions or sizes, and use identical tires on all of their vehicle's wheel positions in order to maintain the best control and stability. Additionally, drivers should never mix winter tires with all-season/summer tires, or mix run-flat tires with non-run-flat tires.
This is one of the reasons that it is desirable to have all of a vehicle's tires wear out at the same time. It's confirmation that the vehicle design, driving conditions and maintenance practices worked in unison to equalize tire wear and performance. It also lets drivers know they got their money's worth out of the current tires and allows them to choose a set of replacements that will either maintain the Original Equipment (O.E.) tires' capabilities, or help tune the vehicle's qualities to even better suit their needs.
Unfortunately wearing out all tires at the same time isn't always possible. Sometimes vehicle design, the use of differently sized tires on front and rear axles, insufficient maintenance and/or driving conditions conspire to prevent it from happening.
If a vehicle's tires don't all wear out at the same time, drivers are typically forced to decide whether they should purchase a new set of tires (forfeiting the worth of the two tires not fully worn out) or just a pair of replacements. While purchasing a new set of tires is best because it will maintain the handling balance engineered into the vehicle while restoring poor weather traction, it is also more expensive. And while purchasing a pair of replacement tires reduces immediate expense, it brings with it the options of choosing exact, equivalent or alternative tires.
Of the three, the best choice is to select the exact tire currently on the vehicle. This assures that the tire's physical dimensions, internal construction, tread design and tread compound are equal to the tires being replaced.
The second option is to choose equivalent tires from the same tire performance category that share the same speed rating, handling and traction characteristics of the original tires. While this isn't as desirable as selecting the exact tire currently on the vehicle, it can become necessary when the original tires are no longer available.
The third option, choosing alternative tires, should only be considered as a temporary solution in an emergency situation. Using alternative tires from different tire performance categories, with alternate sizes or different speed ratings can unbalance the vehicle's handling in poor weather or when pushed to the limit in an emergency.
Because tires play such an important role in every vehicle's comfort qualities and handling capabilities, it is always best to drive on tires that are identical in every detail, including tire brand, model, size and remaining tread depth. Anything else involves some type of compromise.