The Origin of Speed Ratings
We can thank Germany's famous Autobahn for tire speed ratings. Tire speed ratings range from A (the lowest) to Y (the highest). But the chart is not completely in alphabetical order. For example, H is between U and V, with the common perception that H stood for "high performance" at one time. As manufacturers continue to add speed to their vehicles, tire speed ratings evolve to match the speeds. For example, Z was the highest rated speed at 149+ until W & Y were used to match the higher speeds of exotic sports cars.
Speed Ratings Refer to More Than Just Speed
Speed ratings make a difference not only in regards to speed, but in regards to ride comfort, wearand cornering ability. Typically, the higher the speed rating, the better the grip and stoppingpower, but the lower the tread life. You can always increase the speed rating of the tires on your vehicle for improved performance, but can never decrease it without reducing the vehicle top speed to that of the lower speed rating selected. In many countries, the law requires that tires must be specified, and fitted, to exceed the maximum speed of the vehicle they are mounted on, with regards to their speed rating code.
A tire's speed rating is an indication, expressed as a letter code on the sidewall of the tire, of a speed the manufacturer expects the tire to be able to sustain over a long period of time without failing. The top speed rating semi-alphabetic code and the corresponding top speeds are:
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