How To Read Tire Sizes

Knowing how to read tire sizes is easy to do once you know what the markings on the side of the tire represent. The markings on the tire let you know everything about the tire from what type of vehicle should be using it to the maximum amount of speed the tire can roll safely. The size of the tire is easy to determine when you know what to look for in a tire.

Every vehicle will have the recommended tire size usually found on the inside of the door or the door to the fuel tank. However, it is up to the owner of the vehicle to make the final decision to what size tire he wants to drive on safely, so make sure you have the correct tire put on your vehicle by knowing how to read the size of the tire.

Things you'll need:

• A tire

Here is an example of what can be printed on the side of a tire: P255/50R16 91S

1. The first letter on the tire identifies the type of vehicle that can safely use the tire. When the tire has the letter "P," this means the tire was made to fit mainly on passenger vehicle. 
2. The numbers after the first letter tells you the width of the tire in millimeters. The tire showing the number 225 indicates that the tire is 225 millimeters across from the widest point of its outer sidewall to the widest point of its inner sidewall when mounted and measured on a specified width wheel. The following numbers after the slash mark are the measurement from the edge of the inner rim to the thread of the tire itself, so with the tire showing "50" indicates the height of the tire's sidewall.
3. The letter following the tire's sidewall height represents the internal construction of the tire. The R on tells the owner of the tire that it is made of radial but which is usually the construction of a tire, however there are some tires that will have a D and that will stand for diagonal which is a bias ply construction which is seen on light size trucks and spare tires. 
4. The "sixteen" on the example tire is the wheel's diameter in inches and the size rim that the tire will fit. The numbers you will usually see on a tire are sixteen, but the wheel's diameter can also size eight, ten, twelve, thirteen, fourteen, fifteen, sixteen, seventeen, eighteen, nineteen, twenty, 22, 23, 24, 26 or 28. It is important to get the correct wheel diameter because if the tire is too large or small for the rim, it will not fit properly and will come off while driving. 
5. The last set of numbers and letters represent the maximum speed and weight for the tired. Some people don't realize that every tire is tested for the amount of weight it can carry and the maximum speed it can safely roll. You should definitely be aware of these two symbols because only you know how much weight will be in your vehicle and how fast you enjoy driving.