You probably have noticed a group of letters and numbers on the sidewall of your tires before, not everyone knows what they mean. They may seem a bit perplexing, but they are actually pretty easy to get. For this example we'll use one of the most common tire sizes: P215/60R16 89S.
First Things First
In this case the P is P-metric (or you can simply think Passenger) meaning that the tire is meant for use on Passenger vehicles. This can include SUVs, Light Trucks, Vans, and certainly the average cars.
They could also be:
T which is stamped on the spare - it means temporary.
LT which for Light Truck metric and is designed for tires on autos made for carrying sizable loads and trailers. SUVs and Trucks will often have these.
C means for commercial and will commonly be seen on delivery trucks and vans that are designed move big loads.
ST which stands for Special Trailer and really should only be used on utility, boat, or car trailers. They should not be used on regular cars or light trucks.
If the tire does not show a letter first it just means the tire size is metric size and usually seen on cars from Europe.
To learn about what style or tire you should use try reading: Winter,Summer,and All Season Tires
This is the three numbers after the first collection of letters. It means how wide the tire is from the widest part of the outside sidewall to the widest part of the inside sidewall. In this case the numbers stand for 215 mm (nearly 8.5 inches - just divide the number by 25.4 to find it in inches).
Following the first set of digits and the right slash is a 2 digit value that is in place for the tire's aspect ratio. This is the percentage of the tire's sidewall height compared to the section height. In this explanation it is 60 which means the section height is nearly five inches. The higher the value is the taller the sidewall is and vice versa.
Following the aspect ratio value is a letter or two (R in this explanation). This stands for the tire's internal construction. Here we have an R which stands for radial. This will appear on nearly all cars. Another example is D which means the plies are diagonal. This will most commonly be seen on spares and light trucks. If the letter is a B it stands for Belted and implies that the plies crisscross and are also reinforced with belts. This will not be seen on many cars these days.
And in fifth...
With the second group of letters you can find a second letter, most usually Z, which stands for the tire's speed rating.
The Final Lap
A lot of tires will now have a final collection of letters and numbers. These stand for the tire's Service Description. They rate the speed rating and load index. In this case the last three are 89S. What this means is that the tire has a load index of 89 and a speed rating of S. S means the tire is secure at speeds of up to 112 mph. 89 means the tire can support 1323 pounds (remember, this is per tire).
Hopefully this has helped show how tire ratings and sizes are defined. If you wish to learn more about tire sizing or what OEM or new tires will fit on any car visit Tire Specs or if you plan to find out about the scores each individual tire has been given by the Government consider looking at UTQG Scale