Explaining auto tire sizes is not as difficult as it seems. At first all those numbers and letters seem random. But the following will make them easier to read.
In this example, the sidewall on the tire says P225/50R16 91S. The letter P means Pmetric, the standard definition for tires used in America. Vehicles with the P marking include trucks, SUVs and passenger vehicles.
The numbers after the P refer to the measurement of the sidewall. This is at the tire sidewall’s widest point. The /50 determines the profile of the tire from tread to rim. The number refers to the height of the sidewall.
The next step to explaining auto tire sizes is to define the R in the tire. The R stands for radial tire. If the tire is radial, plies are going to radiate from its middle area. A D means diagonal plies. This is utilized on light trucks and spares. A belted tire will have the letter B on it.
The two numbers after the R indicate the tire diameter. The diameter referred to is that of the wheel rim and tire. Needless to say, diameters vary greatly among cars. The variation will be even greater with other vehicles.
The final codes denote the speed ratings and load. They indicate maximum tire performance under normal circumstances. Load rating tells you how much weight the car tires can handle. The speed points out the maximum speed the tires can travel. Again, this is under the optimum conditions. If the weather conditions are not ideal, the performance of the tires will be different.
Not all tires have the same numbers and letters. The letter P is usually assigned to vehicles that don’t weigh more than a half ton. The P designation only applies to American tires. It does not apply to European tires. If you see a letter T, it denotes a spare or temporary tire. Light trucks sometimes use the LT designation rather than P.
LT can only be used by SUVs, pickups and trucks that don’t exceed one ton. Delivery vans and trucks often use C rather than P. ST means special trailer service. They are typically used by utility trailers, boats and other service vehicles
As you can see, explaining auto tire sizes is not that hard. The numbers and letters will differ. But they all indicate a tire’s speed, load capacity and purpose.