You probably have noticed a set of numbers and letters on the side of your tires before, but not all know what they mean. They may seem a little perplexing, however they’re really very simple to understand. In this case we’ll focus on one of the most purchased tire sizes: P 215 / 60 R 16 89S.
In this case the P is P-metric (it can be remembered as Passenger) meaning that the tire is meant for use on Passenger vehicles. This can include Light Trucks, SUVs, Vans, and certainly regular cars.
Others you may find are:
T which is placed on the spare – it stands for temporary.
LT is for Light Truck metric and is designed for tires on automobiles capable of carrying sizable loads and trailers. Trucks and SUVs will often have LT tires.
C means for commercial and will typically be seen on vans and delivery trucks that can move big loads.
ST means Special Trailer and really should only be used on utility, boat, or car trailers. They should never be put on regular cars or light trucks.
If your tire doesn’t contain a first letter it simply means the tire size is metric size and mostly found on cars in Europe.
This is the collection of numbers after the first set of letters. It defines how wide the tire is from the widest portion of the outside sidewall to the widest part of the inner sidewall. In this case the value is 215 millimeters (nearly 8.5 inches – simply divide the value by 25.4 to see it in inches).
Following the first group of digits and a slash is a two digit value that defines the tire’s aspect ratio. This is the percentage of the tire’s sidewall height in comparison to the section height. In this case it is sixty which means the section height is nearly five inches. The larger the number is the taller the sidewall is and the lower the number the smaller the sidewall will be.
After the second set of numbers is a letter or two (R in this case). This stands for the tire’s construction type. R means that the tire is a radial. This will be seen on most all cars. Another letter you may see is D which means the plies are diagonal. This will most usually be found on light trucks and spares. If the letter is a B it stands for Belted and implies that the plies are reinforced with belts and are crisscrossed. This will not be seen on many cars these days.
Together with the second group of letters you can sometimes spot a second letter, most likely a Z, which stands for the tire’s speed rating.
Many tires will also have a final set of numbers and letters. The Service Description for the tire can be found here. They define the speed rating and load index. In our example the last three are 89S. This means that the tire has a load index of 89 and a speed rating of S. 89 equates to 1323 pounds (per tire). S means the tire is safe at speeds of up to 112 miles per hour.
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