Understanding Tire Load And Speed Ratings

The tire load index indicates the maximum weight a tire can bear with proper inflation (as recommended by the manufacturer). Tire speed rating indicates the fastest speed the tire can reach before its performance is affected by driving forces (temperature, friction, rolling resistance).

Tire Load Index

The tire load index is a code expressed in numbers indicating the maximum load the tire can safely handle whenever properly inflated. The number is found on the tire sidewall varying typically between 75 and 150, and it corresponds to a weight capacity in pounds (or kilograms) to a standardized chart.

Tire Load Index Chart

A tire load index chart is a standardized table indicating the tire's load capacity at the pressure recommended by the manufacturer. The key components of the tire load index chart are the load index numbers (typically from 0 to 150) and the tire weight capacity (in kg or lbs) corresponding to each load index number.

To read tire load capacity, find the load rating number on the tire sidewall. For example, a tire with a sidewall marking “225/40 R 18 94 Y” has the “94” load index. This index refers to a tire weight capacity of 1,477 lbs according to the tire load index chart. This means that a 4-tire vehicle has a total load capacity of 5,908 lbs as the tire load capacity is multiplied by the number of tires.

_{Tab. 1. Tire load Index Chart}

Tire Speed Rating

The tire speed rating denotes the maximum speed at which the tire can safely perform on the road while carrying the vehicle's weight until driving forces affect its performance (rolling resistance, temperature, friction). The speed rating is marked by symbols from A to Z, which drivers can find at the end of the tire's sidewall marking. These letters are read according to a standardized speed rating chart.

Speed Rating Chart

A tire speed rating chart is a standardized table indicating the maximum speed the tire can safely handle. The key components of a tire speed rating chart include the speed rating letter (from A to Z) and the actual maximum speed (in mph or km) corresponding to the speed letter. For example, the "Y" speed rating on a “225/40 R 18 94 Y” sidewall marking corresponds to 186 mph, which is the maximum recommended speed limit to drive safely.

_{Tab.2. Tire Speed Rating Chart. *The ZR symbol may appear instead of W or Y in the size designation for tires having a maximum speed capability above 149 mph. The ZR designation including the (Y) speed symbol must appear on the tire sidewall for tires capable of withstanding over 186 mph.}