How to Know if you Have Unidirectional Tiresby Jody L. Campbell
A unidirectional tire is also referred to as a directional tire. This means that the tread pattern of the tire is formed to rotate on the vehicle in only one direction. This prohibits a crossing pattern for tire rotations, and also can result in faster tire wear. However, the unidirectional tire offers better traction for traveling on wet or snowy roads. Most tires on cars are symmetrical or non-directional tires.
Read the information on the sidewall of the tire. There will be one of two possible indicators stamped on the sidewall of a unidirectional tire: Either an arrow will be pointing in the direction of a forward motion on the sidewall (in which case every tire on the vehicle should have the arrow pointing to the front of the vehicle), or there will be printed words saying "This Side Out."
Look at tread pattern of each tire. A unidirectional tire's tread pattern will form into the shape of a "V" as you face the front of the tire. Symmetrical tires will offer a tread pattern that goes in one direction up to the center of the tire, and then the tread pattern will form in the other direction for the remaining half. This ensures that regardless of how the tire is mounted, it will not matter.
Inspect all the tires on your vehicle. Do not assume that they are all unidirectional or otherwise, especially if you bought the car used. It is possible to have mixed tires and have unidirectional and non-directional tires on the same vehicle. Although a misplaced unidirectional tire on a vehicle is not necessarily a safety hazard, it will compromise the performance of the tire and should be corrected.