The tire data on the side of the tire will be in the form of this example: 235/60R17 102T. The 235/60R17 is the tire size, the 102 is the tire's load rating index and the T is the indicator for the maximum speed rating. Tire sales literature also will display the load and speed indexes in the same format.
The load rating on car and light truck tires ranges from 70 to 110. A tire with a load rating of 70 can carry 761 pounds, while a 110 rating has a load capacity of 2,337 pounds. A tire with a 101H load and speed index is rated for a maximum load carrying capacity of 1,819 pounds. A tire with a 102T rating is capable of safely supporting 1,874 pounds. The load is per tire, so a vehicle with 101H tires has a maximum curb weight of 7,276 pounds, and one with 102T tires can carry 7,496 pounds.
The letter-indicated speed ratings are the maximum speed at which a tire can be safely driven. Speed ratings are indicated by the letters L,M,N,P,Q,R,S,T and U, increasing in 10-kilometer-per-hour increments starting at 120 kph for L. Then H, V, W and Y step up in that order at 30-kph increments. Conversion to miles per hour means an L-rated tire has a maximum speed of 75 mph and a Y-rated tire can be run up to 186 mph. The tire with the 101H index is "H" speed rated to a maximum of 130 mph. The 102T tire has the lower "T" speed rating of 118 mph.
A vehicle with tires that have a load and speed index of 101H can be safely driven with a maximum weight of 7,276 pounds up to a speed of 130 mph. The 102T tires will support a weight of 7,497, but should not be driven faster than 118 mph. Both tires have relatively high load ratings. For comparison, a Chevrolet Equinox that uses tires in this load range weighs about 4,000 pounds, leaving more than 3,000 pounds of load capacity.
Vehicle manufacturers recommend against installing replacement tires with lower load and index ratings than the original equipment tires. Installing lower-rated tires can compromise the safe operation of the car. Also, the load and speed ratings are dependent on the tires being inflated to the correct pressure. Under-inflation will significantly reduce the load and speed capability of a tire.
The data printed on the sidewall of a tire provides all of the information someone needs to evaluate whether the tire is appropriate for the intended purpose. Included with tire size and application is information concerning the maximum load and speed for which the tire has been designed and tested.