AKRON-Tire dealers in the U.S. may begin spotting a couple of new speed rating symbols on high performance tires due to engineering that keeps pushing vehicle speed capabilities higher. Until recently, the ``Z'' symbol in the tire size designation covered all tires with maximum speeds above 149 mph.
But as more vehicles race into the market with higher speed capabilities, the U.S. tire industry has decided to designate two more speed categories: ``W'' and ``Y.''
Last year the Tire & Rim Association adopted the ``W'' and ``Y'' symbols as subgroupings of the ``Z'' speed rating. These symbols appear in the service description, which includes the load index.
The ``W'' denotes a maximum speed of 168 mph; ``Y,'' a maximum speed of 186 mph.
When the ``W'' or ``Y'' appears in the service description, a ``Z'' may or may not appear in the size designation. However, tires with maximum speed above 186 mph must have a ``Z'' in the size designation.
For example, a passenger radial with a maximum speed of 168 mph would be identified: P275/40R17 93W or P275/40ZR17 93W.
The ratings originated in Europe and will be seen in the U.S. mainly on imported replacement tires or original equipment tires on European cars, according to the Tire & Rim Association.