Speed ratings are designed to match the speed capability of tires with top speed cababilities of performance vehicles. Tire manufacturers do not recommend the use of their products in excess of legal speed limits.
How does a tire manufacture determine the speed ratings for their tires? Speed ratings are based on laboratory tests: a tire is pressed against a large diameter metal drum to reflect its appropriate load, and run at ever increasing speeds (in 6.2 mph steps in 10 minute increments) until the tire's required speed has been met.
Note: Speed ratings only apply to tires that have not been damaged, altered, under-inflated or overloaded. Most tire manufacturers maintain that a tire that has been cut or punctured no longer retains the tire manufacturer's original speed rating, even after being repaired, because the tire manufacturer can not control the quality of the repair.
When Z-speed rated tires were first introduced, they were thought to reflect the highest tire speed ratings that would ever be required, in excess of 240 km/h or 149 mph! While Z-speed rated tires are capable of speeds in excess of 149 mph, how far above 149 mph was not identified? That ultimately caused the automotive industry to add W and Y speed ratings to identify the tires that meet the needs of new vehicles with extremely high top-speed capabilities.
When a Z-speed rating appears in the tire size designation, the Z in the size signifies a maximum speed capability in excess of 149 mph, 240 km/h. The W in the service description indicates the tire's 168 mph, 270 km/h maximum speed. When the Y-speed rating indicated in a service description is enclosed in parentheses, the top speed of the tire has been tested in excess of 186 mph, 300 km/h. As vehicles have increased their top speeds, tire speed ratings have evolved to better identify the tires capabilities, allowing drivers to match the speed of their tires with the top speed of their vehicles.
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SYMBOL DESIGNATION
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MPH
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km/h
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VEHICLE / TIRE TYPES
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Y
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186
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300
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Exotic Sports Cars
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W
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168
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270
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Exotic Sports Cars
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V
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149
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240
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Sport Sedans, Coupes, Sports Cars
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U
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124
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200
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Sport Sedans, Coupes
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T
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118
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190
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Family Sedans, Vans
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S
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112
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180
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Family Sedans, Vans
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R
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106
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170
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H.D. / Light Truck Tires
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Q
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99
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160
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Studless / Studdable Winter Tires
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P
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93
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150
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N
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87
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140
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Temporary / Spare Tires
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M
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81
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130
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