TECH CENTER - TIPS TO HELP UNDERSTAND SPEED RATING

Tips to Help Understand Speed Rating, Service Descriptions and Load Index

If we use a P205/55/R15 88V tire size as an example, the 88V is the service description. A service description lists a tire’s speed rating and load index. This information is required on all speed rated tires since 1991 (except for Z rated tires). The first two numbers of 88V indicated the tires load index and then is followed by a letter (V for example), this indicates the speed rating.

Speed Rating

Some roadways around the world, have different laws and do not require speed limits. Speed ratings were created to match the speed capabilities of a vehicle to the same speed capabilities of a tire. Some tires are manufactured to reach very high speeds, although manufactures always recommend to never use their tires in excess of the legal speed limit posted. The ratings are obtained in a laboratory where a tire is pressed against a large metal drum used to reflect the applied load. The tire is then run at increasing speeds, (6.2 mph increments every 10 minutes) until the required speed is met.

Speed ratings only apply to tires that have never been damaged, loaded incorrectly, over/under-inflated. Even if the tire is repaired i.e. a tire patch or a tire plug, the manufacturer retains the original speed rating. Here are a few examples of how the speed rating has been marked on tires:

225/50SR16

225/50SR16 89S

225/50R16 89S

All of these examples are accepted as ways of identifying speed ratings.

225/50SR16	112mph, 180km/h
225/50HR16	130mph, 210 km/h
225/50VR16	in excess of 130mph, 210km/h

Here are the most common seed ratings and their descriptions

L	75mph	120km/h	Off-Road & Light Truck Tires
M	81mph	130km/h	Temporary Spare Tires
N	87mph	140km/h
P	93mph	150km/h
Q	99mph	160km/h	Studless & Studdable Winter Tires
R	106mph	170km/h	H.D. Light Truck Tires
S	112mph	180km/h	Family Sedans & Vans
T	118mph	190km/h	Family Sedans & Vans
U	124mph	200km/h
H	130mph	210km/h	Sport Sedans & Coupes
V	149mph	240km/h	Sport Sedans, Coupes & Sports Cars

Z-speed rated tires were first introduced as the highest speed rating in excess of 149mph. Although a z-speed rated tire is rated above 149mph, it is not specified exactly how much further than 149mph it is capable of going.  This eventually lead to the creation of W- and Y- speed ratings to identify exact mph specifications for the needs of newer vehicles that have very high top-speeds.

W	168mph	270km/h	Exotic Sports Cars
Y	186mph	300km/h	Exotic Sports Cars

Even though the Z-speed rating still appears in the tire size, such as 215/40ZR16 91W, the Z shows that the tire is capable of going in excess of 149mph, 240km/h; the W, however, states that the tire should not exceed 168mph. Most recently, tire manufacturers have included a Y-speed rating in the service description in parentheses such as 295/35ZR20 (99y). The top speed of this speed rating is in excess of 186mph as shown below:

285/35ZR19 99Y	186mph, 300km/h
285/35ZR19 (99Y)	in excess of 186mph, 300km/h

 

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