The numbers you see on the sidewall of a tire, contain valuable details about the tire. The alphanumeric code holds in itself the complete description of the tires, which helps people decide whether a tire is suitable for their vehicle or not.
A typical code on a Light Truck & SUV tire looks like; 35(Diameter)x12.5(Width)R20(Rim Size) E(Ply Rating) and our tires will have another spot on the tire with Load Index and Speed Rating. A speed rating will be an alphabetic number ranging from L-Z stating how fast the tire is rated for. If you are driving then you should know that the code on the sidewall, contains details of the tire from the speed rating to the manufacture details. Reading and understanding the speed rating chart will let you know the service description of the tire. The speed rating is usually located next to the load index, which will tell you how much weight the tire can hold. The load index will typically be first and then the speed rating. For instance, our Claw 35x12.5R20 E has a load index of 121 and a speed rating of Q. To understand the actual meaning of the code, you need to read a tire speed rating chart.
Understanding the Speed Rating and Reading the Speed Rating Chart
Speed rating on the tire displays the top-speed of the vehicle at which a tire safely functions, beyond this, it is not safe to use the tire, and it may burst. Locating a "Q" on a TreadWright sidewall would indicate the top of 99mph. The speed rating that you will find on the tires may be from the following; L, M, N, P, Q, R, S, T, H, V, W and Z. The tires with a rating from M to W, are designed to perform at top-speeds from 130mph to 186mph. For tires intended for vehicles with a top speed higher than 149mph, are assigned with a Z-speed rating.
Understanding the Z-Speed Rating
When the manufacturers designed the Z-speed rating tires, they did not specify the top-speed at which these tires were capable of functioning perfectly, without wear-and-tear. To specify the maximum speed rating for Z-rated tires, the manufacturers began to add W, Y, and (Y) ratings to the code. Therefore, a tire with a Z-speed rating has a code similar to 225/50ZR16 91W. The Z in this code specifies that this tire is perfect for vehicles with a top speed higher than 149mph, and the additional W-rating displays that it is safe to use for a vehicle with a top speed of 168mph. A Y-speed rating on the tire is an indication that it is safe to use the tire for a vehicle with a top speed of 186mph, while (Y)-speed rating specifies that the tire is perfect for a vehicle with a top speed of 186mph.