Understanding Semi Truck Tire Size

Having the correct semi-truck or 18-wheeler tire size is vital in the operation of any size fleet of trucks. Properly operating tires impact the bottom line regarding the amount of time the trucks can be on the road and the safety of your operators and others on the road. Having the wrong semi-truck tire size can mean that general wear and tear happens faster. The size matters when understanding how the placement of each tire. More maintenance or less time on the road means your payload is not being delivered.

Common Semi-Truck Tire Sizes

Over the last few years, the most common truck tire sizes include but are not limited to 295/75R22.5, 275/80R22.5, and 225/75R19.5. While these cover average truck tire sizes and the list is good information to have, it is not ultimately helpful if you don’t understand what these numbers mean to you and your truck/s.

If we take that first size, 295/75R22.5 and explain how semi-truck tires are sized, those numbers break down into several informative categories.

Truck Tire Sizes Explained

Tire width - The first number in the series denotes the tire width. Semi-truck tire width can be displayed in terms of inches or millimeters. In this case, a 295-inch wide tire would be massive, so a quick assumption can be made that this is a millimeter marking. Having the correct semi tire width is vital as it is literally where the rubber meets the road.

Aspect Ratio - The second notation (75) after the slash mark is the aspect ratio. It represents the percentage of the length of height to width. This number is an important sizing calculation in tire fitting, and along with rim diameter will help you determine your best tire and wheel combinations.

Tire Construction Type - In this example, the letter R stands for radial (this notates that the steel belts inside are running 90-degrees from the direction the tire is facing). If you see a dash, then the tire is bias-ply (this notates that the nylon belts running anywhere from 30 to 45-degrees from the direction the tire is facing). Much less common are B for bias belt and D for diagonal.

Rim Diameter - The following number, in this case, 22.5, is the diameter. This does not apply to the diameter of the whole tire, but rather the semi-truck wheel diameter (the hole in the center of the tire). You would need a 22.5-inch wheel to fit this tire.

When reading the sidewall, you will encounter two additional numbers.

Load index - This number will indicate how much weight or load carrying capacity a single tire can hold. For example, 89 = 1,279 pounds, while 88 = 1,235 pounds.

Speed rating - You will see a speed rating letter at the end of the string. This indicates how fast the tire can go under its maximum load. A tire can go faster than this number at a lower load, but typically the tires can withstand a higher speed than the speed limits you will encounter.  

How can GCR Help You Find the Right 18-Wheeler or Semi-Truck Size Tire?

No matter the size of your fleet or the needs that your trucks meet, we have the right tires for you. Whether you are looking for steer tires, drive tires, trailer tires or all position tires, we can outfit every wheel position of your commercial truck. Whether you’re looking for a top-tier fuel-efficient tire or a more economical option, we carry a wide variety of brands and semi-truck tire sizes, and we can get you and your truck back on the road quickly.