Understanding Tire Side Wall Markings

It is good to understand the markings on the side of a tire because it provides a wealth of information. The name of the manufacturer and the name of the particular tire are obvious. Start by looking close to the bead by the wheel. The size of the wheel will be depicted in metric, along with the type of wheel, such as bias or radial. The size on a tire is important to understand. For example a 225/45/17 is broken down thusly: The 225 is in millimeters and relates to the width of the tire. To convert this to inches just divide the 225 by 25.4 and you have 8.86 inches. The next number, "45," is the percentage of height to width. In this case the tire is 45 percent as tall as the tread is wide. Lastly the final number is simply the size of the rim which is 17 inches in diameter.

Further down on the side is the load rating and the maximum tire pressure. The load will be specified in pounds under maximum pressure. This is per tire. A stamp with two numbers followed by a letter designates the load rating and most importantly, the speed rating. The reason the speed rating is so important is that it relates to the ability of the tire to dissipate heat at high speeds. These speed ratings show the safe speed the tire can be operated at for extended periods of time without coming apart. An "S" is 113 miles per hour, an "H" is 131, and a "Z" is over 131. Now, not many people will drive at these speeds, however it does mean how long the tire will last and how good it handles.

In order for a tire to have a high speed rating, means that it has a serious sidewall resulting in less tire bend in turns giving excellent handling in comparison to a slow speed rated tire. This is because these tires have much more steel in the bead and a much stiffer sidewall. Place an "S" rated tire (unmounted) next to a "V" rated tire and push down on it. The S rated is much softer and can be readily flexed where you can sit on a V rated tire and it will barely flex.

Moving along the side of the tire you will see a temperature rating: A, B or C, followed by a treadwear number such as 450. These numbers are particularly important when buying a tire. The higher the temperature letter -- A being the best -- means the tire will run cooler which relates to harder tread. The treadwear is the minimum mileage the tire is expected to go, in this case 45,000 miles.

Another number on the side wall starts with the letters "DOT," for department of transportation followed by the compliance number. Next to this number are four more numbers -- the first two are the week of the year the tire was produced and the last two are the year.

If the tire has an M/S on the sidewall it means the tire should do well in the mud and snow. This is not very reliable through experience. A good snow or mud tire must have tread that is far apart to keep the snow from packing in between the treads and turning the tire into a snowball.

Lastly, move from the sidewall for a moment and look at the tread on the tire. Notice that between the tread and evenly spaced are small protrusions or humps. Normal passenger car tires start at 11/32 of tread. The hump represents 2/32 of tread. This is where the tire must be replaced. When a tire's tread gets this low, the tire becomes much more susceptible to puncture and separations.