Ever wonder what the letter in your tire size means? For example, the "Z" in 245/45ZR17 or the "H" in 205/55R16 89H. This letter is the speed rating of the tire.
Tires are tested in laboratory conditions under load by tire manufacturers to determine the maximum speed capability of the tire.
Shown below is what the speed rating letter equates to in MPH.
|L||75 mph||120 km/h||Off-Road & Light Truck Tires|
|M||81 mph||130 km/h|
|N||87 mph||140km/h||Temporary Spare Tires|
|P||93 mph||150 km/h|
|Q||99 mph||160 km/h||Studless & Studdable Winter Tires|
|R||106 mph||170 km/h||H.D. Light Truck Tires|
|S||112 mph||180 km/h||Family Sedans & Vans|
|T||118 mph||190 km/h||Family Sedans & Vans|
|U||124 mph||200 km/h|
|H||130 mph||210 km/h||Sport Sedans & Coupes|
|V||149 mph||240 km/h||Sport Sedans, Coupes & Sports Cars|
|W||168 mph||270 km/h||Exotic Sports Cars|
|Y||186 mph||300 km/h||Exotic Sports Cars|
While a Z-speed rating still often appears in the tire size designation of these tires, such as 225/50ZR16 91W, 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.
You can learn more about speed rating and the other letters and numbers on the sidewall of your tire in "How to Read Speed Rating, Load Index & Service Descriptions."
Disclaimer: It is important to note that speed ratings only apply to tires that have not been damaged, altered, underinflated or overloaded. Additionally, most tire manufacturers maintain that a tire that has been cut or punctured no longer retains the tire manufacturer's original speed rating.