March 25

Truck and Trailer Tires: Understanding Load, Sizes, and More

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If you drive a work truck, a lot rides on your vehicle. And your truck relies on durable, long-lasting performance tires. 

Are your tires the most suitable tires for your truck? Do you know how to select the best tires for your truck? 

Determining the best tires for your truck means understanding how you use your truck affects your tires and means having a thorough knowledge of tire performance characteristics. 

How to read your tires 

Knowing which tires you should install on your truck starts with knowing how to read a tire. 

The tires for trucks classified as light duty have a marking that begins with LT. The letter(s) at the beginning indicate tire type. LT stands for light truck; P stands for passenger; ST stands for special trailer; and T stands for temporary.

Light-duty trucks have a gross vehicle weight rating (GVWR) of up to 10,000 pounds and are classified as truck class sizes 1 and 2. Examples of light-duty trucks include the base truck versions of all popular, non-commercial truck manufacturers, such as Ford, Chevy and Toyota. 

Tires for medium-duty and heavy-duty trucks have different specification markings and will be discussed next.

Following the LT on light-duty trucks is a number. This number represents the width of the tire (measured from sidewall to sidewall) in millimeters. Many tires will be in the 200’s. 

This number is followed by a backslash and another number (two to three digits in length) that outlines the aspect ratio of the width to the height, so the number 60, for example, indicates the tire’s height sidewall is equal to 60 percent of the tire’s width. 

This number is followed by a letter that indicates the tire’s construction type. The most common letter is R; it stands for radial. Radial tires have layers of fabric of the tire is constructed of cords running at right angles to the circumference of the tire. Off-road trucks and construction equipment usually come equipped with bias tires, which are marked with a “B”.

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Compared to bias tires, radial tires are more flexible, so they offer a better long-drive ride and they last longer and cost more. Bias tires, on the other hand, are solid and robust compared to radial tires; they are less likely to get damaged or punctured, so they are better suited to off-road driving.

This letter is followed by a two-digit number, which represents the tire’s rim diameter measured (from tread to tread) in inches.

Following the rim diameter is another two or three-digit number, which indicates the tire load range that can safely be placed on the tire. So, a truck that weighs 9,000 pounds (which is near the top of the weight range in the light-duty truck segment) may have tires rated at 120; 120-rated tires have a maximum weight of 3,086 pounds. When you multiply that by four tires, that results in a total of 12,344 pounds, which means the 9,000-pound truck can carry up to 3,344 pounds (payload plus people).  

You needn’t factor in the weight of anything towed—only the weight of what is hauled. Towed loads rest fully on their own tires.

Next is the tire’s speed rating; this number corresponds to a maximum speed that the tires can safely perform. Letters that appear early in the alphabet correspond with low speeds and letters that appear later in the alphabet denote faster safe driving speeds. For example, tires marked with the letter D can be driven up to 40 mph, tires marked with the letter L can be driven up to 75 mph and tires marked with the letter Q can be driven up to 100 mph. 

Following the speed rating may be more letters or a symbol. These indicate special performance features such as snow tires or high-performance tires. 

The final component of this set of codes is the name of the manufacturer of the tire. 

Reading the fine print 

This marks the end of the larger alphanumeric markings on the tire. Near the rim of the tire are more markings, which relates some new and duplicate information. 

The letters DOT, which stands for Department of Transportation, indicate that the tire has met all DOT regulations. The alphanumeric sequence succeeding DOT is a code created by DOT to help track tires after being sold. This sequence is called the Tire Identification Number (TIN) and consists of up to 12 alphanumeric symbols to identify where and when the tire was manufactured.

Succeeding the TIN are indicators of the tire’s composition and materials used. An example is 10 Plies chord. This indicates the tire has a chord composition and the 10 plies is a measure of the tire’s load rating—also called load range, load index or ply rating. A higher ply count contributes to a greater load carrying capacity. 

Historically, the ply rating used to express the literal number of layers in the tire, but now it’s a measure of the tire’s strength.

The next string of information pertains to the tire’s treadwear, traction and temperature. The Uniform Tire Quality Grade (UTQG) treadwear rating is expressed as a number. Higher numbers indicate greater tread, resulting in longer life. Traction is expressed as a letter (AA, A, B or C); AA offers the best traction and C offers the worst. And, temperature, which expresses the tire’s ability to resist and dissipate heat, is also expressed as a letter (A, B or C). Tires marked A have the best reaction to heat and C has the worst. 

The maximum load rating is represented again; this time, it’s expressed in pounds.

Succeeding that is the recommended maximum permissible inflation pressure.

Whether the tire is radial or bias is stated again, this time, in plain English. 

In total, tires reveal a dozen data points by which to compare tires, so knowing how to read a tire in its entirety is essential to selecting the best tires for your truck. 

Larger trucks 

Trucks with a GVWR between 10,001 pounds and 26,000 pounds are considered medium-duty trucks and are classified as truck class sizes 3-6. Garbage trucks, fire trucks, dump trucks and concrete mixers are popular applications for medium-duty trucks. 

With some medium-duty trucks, you need different tires depending on their position on the truck. Tire position on light-duty trucks is irrelevant; you can put the rear tires on the front and the front tires on the rear. They are called all-position tires. However, tires for medium-duty trucks have different tires for steer and drive positions, since the tires are optimized for those positions. 

Steer tires influence ride and handling; their ribbed tread designs helps channel water away from the tire. Drive tires usually feature lug-type or siped tread designs to increase traction levels on various surfaces.

Heavy-duty trucks have a GVWR of more than 26,000 pounds and are classified as truck class sizes 7 and 8. Trucks that haul heavy cargo long distances fall into this category. 

They require steer and drive tires for the tractor portion and trailer tires for the trailer. Trailer tires must withstand strong lateral and braking forces, along with carrying varying loads. 

Treads reflect application and environment 

When selecting tires for your truck, you should know how much load you expect to put on them, on what surfaces you will drive the truck, and other environmental conditions. 

Having the wrong tires on a vehicle can cause problems, beginning with diminished tread life, which increases costs, and escalating to bursting a tire while driving on the highway, which increases costs, leaves a driver stranded on the side of the road and negatively impacts schedules. 

Manufacturers of medium-duty tires classify tires by application; it works as a convenient way of helping people (who aren’t tire tread aficionados) choose the correct tires. 

Tires are classified by market (waste haul, long haul, construction, forestry, and mining) and by work environment: 

  • Highway/Urban – a smooth tread provides a quiet, smooth ride and longevity
  • Maximum traction – a deep, wide tread provides superior traction in loose soil, gravel, sand and other soft terrains
  • All-terrain – some trucks regularly get driven in all sorts of conditions, so these tires offer adequate off-road traction and better handling while highway driving
  • Winter tires – treads have larger gaps and remain flexible in cold conditions for maintaining grip on snow and ice and in temperatures below 45oF. 
  • All season – an aggressive tread pushes out rocks and dirt for superior off-driving in muddy and snowy conditions
  • High-performance – rated for fast speeds (up to 168 mph); ultra-high-performance tires are rated for speeds up to 186 mph

Some tire OEMs may have different names for their tires, but most truck tires fall into one of these categories. 

Trailer tires 

Trailer tires have less tread pattern variation than truck tires. They all fall somewhere onto the highway—off-road spectrum; highway trailer tires offer greater fuel efficiency and longevity and off-road trailer tires offer greater traction and durability.

However, one choice that is more common on trailer tires is tire width. Trailer tires come in various widths to distribute the weight of the load across a greater surface, thereby decreasing PSI (pounds per square inch). 

The single most important criteria when choosing trailer tires is the tire’s load rating. The tire load rating indicates the maximum load a tire can safely carry. 

When calculating the load rating you need, consider the GVWR of the trailer and the weight of the largest load you expect to tow. Add those two numbers together and divide by four. 

Find the load rating that corresponds to the number you just calculated, and then choose the tire with the load rating one higher than the one you calculated. It’s best to choose a tire load rating that is higher than what you think you need for two reasons:

  1. The tire load rating is designed to carry the maximum load specified on its sidewall under specific conditions. The first condition is the tire needs to be at optimal inflation, so its ability to carry a load can be compromised if underinflated or overinflated. 
  2. The tire doesn’t have any damage or excess wear, because this can compromise the tire’s ability to carry a load. 

How to examine tires 

When buying used tires (or a used vehicle equipped with tires), there are a number of best practices you should follow. 

  • Read the tire sidewall. Assuming the tire is the right size, you want to check the tire’s load rating and speed rating to ensure it can carry the load you expect to put on it and that it can safely drive at the speeds. Verify the tire’s year of manufacture, the manufacturer, and that it’s DOT approved. Also check for any performance characteristics (such as all-season or mud and snow). 
  • Check the tire tread depth. In most states, a tire is no longer road worthy when tread depth drops below 1/16th of an inch. Stick a penny in the tread, Lincoln’s head first. If the top of Lincoln’s head is exposed, the tire has little to no life left in it. 
  • Check the treads and sidewall for damage, such as cuts, scrapes, punctures, bulges, bumps and cracks.
  • Check for signs of excess wear or irregular wear. Irregular can happen on one side of a tire or the front tires may be more worn than the rear tires or vice versa. 
  • Move the vehicle forward or reverse about a foot to expose parts of the tire that couldn’t be seen previously due to the ground or wheel house. 
  • Check the tire pressure with a tire pressure gauge and when the tires are cool. If the tires aren’t properly inflated when up for sale, what are the chances the owner kept them properly inflated while using them? 
  • Ask if there is any warranty left on the tires. Ask if they have refilled the tires after driving them on insufficient air pressure. Tire association’s and tire OEMs warn end-users not to refill tires that have lost at least 20% of their air and have been driven on; in that case, the tire is considered to be too damaged to safely use.


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