by Tim Plaehn
tire image by Sasha from Fotolia.com
The data printed on the sidewall of a tire provides all the information someone needs to assess whether the tire is suitable for its intended purpose. Information about the maximum load and speed for which the tire has been designed and tested is included with the tire size and application.
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 capacity index, and the T is the maximum speed indicator. The tire sales literature will also show load and speed ratings in the same format.
Car and light truck tire load capacities range from 70 to 110. A 70 load capacity tire can carry 761 pounds, while a 110 has a 2,337 pound load capacity. A tire with a load and speed index of 101H is rated for a maximum load capacity of 1,819 pounds. A tire rated 102T 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.
Lettered speed ratings are the maximum speed at which a tire can be driven safely. 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 increase in that order in 30 km / h increments. Converting to miles per hour means that an L-rated tire has a top speed of 75 mph and a Y-rated tire can run up to 186 mph. The 101H index tire has a nominal “H” speed of a maximum of 130 mph. The 102T tire has the lowest “T” speed rating of 118 mph.
A vehicle with tires having a load and speed index of 101H can be driven safely with a maximum weight of 7,276 pounds up to a speed of 130 mph. 102T tires will support a weight of 7,497, but should not be driven faster than 190 km / h. Both tires have relatively high load capacities. For comparison, a Chevrolet Equinox that uses tires in this load range weighs about 4,000 pounds, leaving more than 3,000 pounds of cargo capacity.
Vehicle manufacturers recommend not installing replacement tires with lower index and load ratings than original equipment tires. Installing lower rated tires can compromise the safe operation of the car. Additionally, load and speed ratings are dependent on tires being inflated to the correct pressure. Underinflation will significantly reduce the load capacity and speed of a tire.