Understanding the letters and numbers on your tire sidewall can be a bit confusing. Tires gives us some insight on how to read a tire size. My simple explanation addresses all the different specifications that are written on your vehicles tire. The sidewall of a tire contains a couple of key features:

Let's Take a Look for Instance at this Tire Size 215/55ZR17 94W

The "215" in the first part of the tire size represents the section width of the tire. The "55" represents the tires aspect ratio or height. The "R" stand for Radial in tire construction and the "17" stands for the wheel diameter in inches. The "94" is the load index and represents the tires maximum load capacity at maximum inflation pressure. The "W" represents the speed rating which is the max allotted speed of a tire.

Another bit of information contained on a tire sidewall is the maximum load capacity. The max load displays a weight at a certain PSI. But this is not the recommended tire pressure that you should inflate your tires to. Instead follow the manufacturer recommended tire pressure setting as seen on the inside of a car's door jam.

Hopefully this video can give you some insight on how to read a car tire.