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Tire Size Explained

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					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.

First Things First
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.

To read about what style or tire you may want to use consider visiting: What do tire
types mean

And in second...
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).

Third Base
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.

Next Up
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.

Next Up
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.

The Final Lap
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.

Hopefully this has helped explain how tire ratings and sizes are defined. If you want
to learn more on tire sizing or what new or OEM tires can fit on your car see Tire
Charts or if you want to learn about the scores each individual tire has been rated by
UTQGS consider reading

				
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posted:1/18/2011
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