SEMI-TRUCK TIRE SIZE In order to safely move all of their cargo, semi-trucks rely on well-built tires to transport them from location to location. These tires are big but just how big? We’ll give you more information about semi-truck tire size and the importance of these items. Semi-truck tire size: A semi-truck tire will have a series of numbers that tells you all the information you need. The first number refers to the tire’s width and is measured in inches or millimeters. The second number is the aspect ratio, which describes the tire’s length. Then there is a letter or symbol which explains the tire type. The final number describes the rim diameter and is usually measured in inches. How many tires are on a semi-truck? A semi-truck is also known as an 18-wheeler, which is directly related to the number of tires it has. Yes, a semi-truck will generally have 18 tires. The trailer itself will only have eight wheels. These are lined up in groups of two, with four on one side of the trailer and four on the other side. The remaining 10 wheels are actually all on the truck itself. There are four sets of two wheels on each side. Then, there are two wheels at the front, with one on each side. While 18 wheels are pretty standard, you can also find semi-trucks with other tire configurations. This can include 10, 26, and 3ven 24 tires, although they are less common. What size tires do semi-trucks use? The size of a semi-truck tire can be quite confusing. For example, one of the most common tire sizes is 295.75R22.5. Another common tire size is 275/70R22.5. Finally, you may also see a tire for a semi-truck marked 225/70R19.5. If you have no idea what these numbers mean, you are not alone. We’ll break down what those numbers mean in the next section. How to determine semi-truck tire size To help you understand the many numbers in a tire’s size, here is what they all mean. We’ll use a standard tire size, 295.75R22.5 as an example. Width Of Tire The width of the tire is how you come up with the first part of a tire’s size. This can still be confusing because some tires will use either inches or millimeters. As the two measurements are vastly different, you may need to use some deductive reasoning. For example, if the number is very large, then the number is more likely an indication of a measurement in millimeters. In our example, the first number is 295, and because it is such a large number, it is obvious it uses millimeters as a unit of measurement. The width of your semi-truck tire is especially important. If you have too narrow a tire, or too wide, it may not fit on the road. Aspect Ratio This ratio refers to the percentage of the length of the tire in regard to height and width. For our example, the ratio is 75, which is very common, although you can also see an aspect ratio of 70 in many other tire models. Tire Type The next category can get a bit technical. You may see an R, which stands for radial, or a -, which means the tire is bias-ply. You can also see a B which stands for bias belt or a D which stands for diagonal. An R, or radial tire type, has steel belts that run at a 90-degree angle away from the direction of the tire. A -, or bias-ply tire type, means there are nylon belts that move between 30 or 45 degrees away from the tire. Rim Diameter Finally, the last number has to do with the diameter of the rim. Note that this is not the entire diameter of the tire, which includes the rubber outside but rather just the inside hole of the tire. For our example, the rim diameter is 22.5 inches. Although this is standard, you can find other semi-truck tires with smaller, 19.5-inch rims. Note that even though the first number in our tire size was measured in millimeters, the last number is measured in inches. What is a load index? Another number that might appear on a semi-truck tire is the load index. This shows what the maximum weight capacity is for a tire to safely hold. The load index is not the weight itself but rather a number that corresponds to it. For example, the number 89 equals a maximum load capacity of 1,279 pounds while the number 88 equals 1,235 pounds. As you can see, the more tires you have, the more total load capacity the semi-truck has. This is why most back tires are doubled up so they can move efficiently and carry more weight. How to choose a semi-truck tire? Start by knowing the types of routes you are most often going to be on. Then, make sure the tires and your weight capacity are all lineups. Always buy new tires, even though it costs more money. Safety is the number one priority for semi-trucks. How long do semi-truck tires last? Semi-truck tires can last between three to six years. There are, of course, many factors that influence this timeline. The first is the terrain the truck is traveling on. Even though semi-truck tires are incredibly durable, constant driving over uneven surfaces can take its toll on the tires. Weather conditions can also affect the lifespan of semi-truck tires. Extreme heat can gradually weaken the rubber, so if the truck is constantly driving through desert areas, the tires can wear out more easily. Even if your tires look okay after six years, it is still recommended to replace them. There may be issues you can’t see by looking at them and you don’t want to take the chance of them not working. Conclusion Semi-truck tires have many different parts to them, and these numbers are reflected in the size numbers. The different numbers will tell you the width, aspect ratio, tire type, and rim diameter.
