It wouldn’t be an 18-wheeler without 18 tires. Considering how tires are a large part of maintenance expenses, it pays to know more about them and how to use them properly for maximum benefit. Here is information regarding tires you might have never thought about, or may just need a refresher.
Standard Versus Commercial
When searching for tires, you might hear of two types: P-metric and LT. P stands for passenger, and LT stands for light truck. Neither of these is used for a semi-truck and you would be best to avoid them.
Commercial tires don’t have a specific typing, so we will just call them commercial tires. Commercial tires tend to have more tread and are made of harder rubber, making them less likely to puncture but also make the drive less comfortable for the driver. They also cost a lot more than a standard passenger tire, in part because of their design and in part because of their size. Don’t try to use a P-metric or LT tire in substitution for a commercial; that’s a safety hazard.
The household name brands that make tires for 4-wheeled sedans also make commercial tires. These include Firestone and Bridgestone. Here are our top picks.
Michelin. Michelin offers some of the best tire warranties in the industry, including three retreads, seven years, and 700,000 miles. That’s enough to drive across the continental United States approximately 233 times!
Goodyear Tires. Another household name for tires, Goodyear tires also have nearly unbeatable warranties. With their Kelly line, you can have unlimited retreads for the first four years. Goodyear also has an online questionnaire to help you find the tire type you need.
Yokohama. Based in Japan, Yokohama has a similar warranty policy to BFGoodrich and heavily focuses on designing with fuel efficiency in mind.
Roadmaster Tires. Roadmaster strives to provide a balance between fuel economy, comfort, lifespan, and price to provide the best value for the average trucker.
The above string of characters might seem like gibberish to the untrained eye, but it tells us a lot about the tire. What does this combination mean? Because each section represents something different, let’s take it one step at a time.
225-Tire width. Tire width can be displayed in terms of inches or millimeters. You should be able to tell which just by looking at the number, a 225-inch tire would be more than twice as wide as the truck itself, and a 9-millimeter tire would be too small for a bicycle, let alone an 18 wheeler.
/80-Aspect ratio. The slash might make you initially think the aspect ratio is the width divided by 80, but clearly, the height of the tire is larger than 3 millimeters. No, this number represents the percentage of the length of height to width, with the slash being a divider to separate the width and the aspect ratio.
R-Tire type. R stands for radial (steel belts inside running 90-degrees from the direction the tire is facing), a dash is bias-ply (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.
22-Diameter. Not the diameter of the tire, but rather the diameter of the hole in the center of the tire. A 22-inch wheel is a perfect fit for this tire.
119-Load index. How much weight a single tire can hold. The further down you go, the more each number adds. 119 is 1,360 kilograms or about 3,000 pounds.
U-Speed rating. How fast the tire can go under its maximum load. A tire can go faster than this at a lower load, and generally, the speed limit will be much lower than your tire’s speed rating anyway. A U rating is 124 MPH.
From this, we can deduce that our mystery tire is a radial tire that fits a 22-inch wheel, is 225 millimeters wide and 180 millimeters in height, can withstand 3,000 pounds and can travel 124 MPH when carrying 3,000 pounds.
The last two bits are confusing because the charts are not linear.
Load Index Chart
Speed Rating Chart
The type of tire is not the only factor in the quality of your drive, but where you place the tire. There are three general locations to put a tire to get different changes in results:
Steer tires. The frontmost tires on your truck, and arguably the most important ones. These tires impact your truck’s handling.
Drive tires. Located where the truck meets the trailer, these tires are the ones turned to make the vehicle move. These tires determine your truck’s grip on the road, so high traction tires are a must during the winter seasons and are still a good idea otherwise.
Trailer tires. Located at the back with the trailer, these tires tend to be especially stiff to better support the weight put upon them.
You can either purchase tires specifically for the position or use all-position tires to place them anywhere. If you place a specifically marked trailer tire in the steering area, though, you may have a hard time steering.
As you drive, your tires will wear down. The thinner the tread, the harder it is to stop. When carrying a full load or hazardous materials, this can prove to be especially dangerous.
All tires are different in how fast they wear down. Check your tires regularly to check the tread. One method is the penny test: take Abraham Lincoln, put him upside down in between the treads, and see how much you can see of him. A penny is 24/32”, so the more you can see of him, the more worn your tires are.
If you can see the top of Lincoln’s head, the tread is 2/32” or less, and you are legally obligated to replace or retread the tire (although it is a good idea to fix it before it gets to 2/32”). The steer tires have even stricter federal regulations: 4/32” minimum, or the entirety of Lincoln’s head.
Aside from normal wear and tear, another consideration is the natural breakdown of rubber in the tires. A tire can last at most six years, even if it is never used. Being in extreme weather conditions such as snow or the summer desert can degrade the rubber at a faster rate.
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