How to Read Speed and Load Rating Index

Using a 195/65/15 91H tyre size as our example, the 91H at the end of the size represents the tyre's service description. A service description identifies the tyre's load index and speed rating. Service Descriptions are required on all speed rated (except for Z-speed rated) tyres manufactured since 1991.

The first two digits (91H) represent the tyre's load index and are followed by a single letter (H) identifying the tyre's speed rating.

Load Index

195/65/15 91H - The load index (91) is the tyre size's assigned numerical value used to compare relative load carrying capabilities. In the case of our example the 91 identifies the tyres ability to carry approximately 615 KG per tyre.

The higher the tyre's load index number, the greater its load carrying capacity.

91 – 615 KG per tyre

92 – 630 KG per tyre

93 – 650 KG per tyre

A tyre with a higher load index than that of the Original Equipment tyre indicates an increase in load capacity. A tyre with a load index equal to that of the Original Equipment tyre indicates an equivalent load capacity. A tyre with a lower load index than the Original Equipment tyre indicates the tyre does not equal the load capacity of the original.

Typically, the load indexes of the tyres used on passenger cars and light trucks range from 70 to 110.

Speed Rating

ZR tyres are for 149MPH and above

Speed ratings were established to match the speed capability of tyres with the top speed capability of the vehicles to which they are applied. Speed ratings are established in kilometers per hour and subsequently converted to miles per hour (which explains why speed ratings appear established at "unusual" mile per hour increments). Despite the tyre manufacturer's ability to manufacturer tyres capable of high speeds, none of them recommend the use of their products in excess of legal speed limits. The maximum operating speed of a vehicle must be limited to the lowest speed rated tyre on the vehicle.

Speed ratings are based on laboratory tests where the tyre 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 tyre's required speed has been met.

It is important to note that speed ratings only apply to tyres that have not been damaged, altered, under-inflated or overloaded. Additionally, most tyre manufacturers maintain that a tyre that has been cut or punctured no longer retains the tyre manufacturer's original speed rating, even after being repaired because the tyre manufacturer can't control the quality of the repair.

Specific Information For Certain Tyres