What You Need to Know About DOT Tire Regulations

Tags: Anatomy of a Trailer, Laws and Regulations

Truck maintenance is extremely important, not just to comply with federal regulations, but to stay safe on the road. The US Department of Transportation’s (DOT) Federal Motor Carrier Safety Administration (FMSCA) maintains sets for numerous regulations for vehicles with the purpose of protecting motorists and surrounding communities.

As a motor carrier or driver, it’s your responsibility to know DOT tire regulations and conduct regular checks to ensure your equipment is always in working order. With the numerous regulations and interpretations of DOT tire standards, it’s helpful to have an understanding of how they may, or may not affect drivers, carriers, and the trailers you tow.

Reference section 393.75 of the FMCSA regulations for a complete list of tire restrictions.

Importance of Checking Tires

Just like a car, commercial trucks and trailers require regular tire maintenance to prevent costly repairs or even accidents. As drivers, your tires are an essential component of your rig, and one of the easiest things to check and maintain.

There are a number of important reasons to stay on top of tire maintenance besides just meeting DOT tire standards. Quality tires that are in good working order will provide:

• Performance: Properly balanced tires with good tread and pressure will help your truck move smoothly on the road. Additionally, investing in higher quality tires can improve performance and efficiency for those long journeys. If you notice the truck pulling or vibrating, be sure to check the tires for damage or lack of tread. Not only will your truck drive well, but you may save some money on fuel with well-balanced tires.

• Safety: Besides moving freight, a driver’s top priority is to practice safe driving habits for the protection of themselves and other motorists. Well-maintained tires give you a better grip on the road­ (especially in wet conditions), the ability to stop faster, and may prevent blown tires, which present serious safety hazards.

• Longevity: Commercial trucks and trailers do a hefty amount of work hauling freight around the country and can be costly to replace. With regular maintenance, drivers, motor carriers, and fleet managers can stay ahead of looming issues and prolong the life of the truck, saving time and money on sudden repairs or purchases.

The benefits are clear, but how often should drivers be checking their tires, and what specifically should they check for? Let’s take a look in the next section.

Commercial Truck and Trailer Tire Regulations

Checking and maintaining tires goes beyond a quick check before heading out on the road. Per the FMSCA and DOT tire regulations, there are specific codes that fall into the Code of Federal Regulations (CFR) which need to be followed.

Section 393.75 in the eCFR specifically addresses tires. The following section details the primary issues to be aware of when checking tires, including specific regulations about overall tire condition, tire tread and grooves, and types of tires permitted.

1. Tread Depth

Per code section 393.75 (c), “tires shall have a tread groove pattern depth of at least 2/32 of an inch when measured in a major tread groove.” It also states that measurements can’t be taken “where tie bars, humps, or fillets are located.” DOT steer tire regulations state that depth is at least 4/32 of an inch. Not following these rules may lead to the driver being cited.

Another consideration are the regulations set by the Commercial Vehicle Safety Alliance (CVSA). They have slightly different measurements that may lead to a vehicle being put out-of-service. Any out-of-service vehicle is subject to FMSCA citations, and each violation must be addressed before the vehicle can be put back in-service.

See below for a quick comparison between the two regulations:

	FMSCA	CVSA
Steer Tires minimum tread depth	4/32 of an inch	2/32 of an inch
Other Tire minimum tread depth	2/32 of an inch	1/32 of an inch

Measurements are to be taken at a “major tread groove,” but there are different interpretations of what that is. For example, the thin decoupling groove on the shoulder of a tire isn’t actually a major groove. Thus, it’s important to check specific grooves that apply to the DOT tire regulations and CVSA regulations to know whether or not tires need maintenance.

2. Inflation Pressure and Flat Tires 

Any tire that is flat or has a leak renders a vehicle inoperable but following inflation pressure guidelines may help prevent flat tires in the future. The DOT tire regulations from the FMSCA for inflation pressure are:

• No motor vehicle shall be operated on a tire that has a cold inflation pressure less than that specified for the load being carried.
• If the inflation pressure of the tire has been increased by heat because of the recent operation of the vehicle, the cold inflation pressure shall be estimated by subtracting the inflation buildup factor shown in Table 1 from the measured inflation pressure.

Inflation Pressure Measurement Correction for Heat:

Table via eCFR

Heat causes tire air pressure to increase, which can lead to inaccurate readings and under-inflated tires on the road. Over time, that can lead to flat tires, which come with a high CSA score that can put a vehicle out of operation.

One note to make is for commercial vehicles that have a defective tire. If the driver removes the defective tire from the axle, it is permissible for them to drive with three tires on an axle instead of four, provided that the remaining tires don’t exceed the maximum weight allowed under section 393.75.

3. Exposed Belt Material

The CSA states that a vehicle is inoperable if it has a tire that:

• Has body ply or belt material exposed through the tread or sidewall
• Has any tread or sidewall separation
• Is flat or has an audible leak
• Has a cut to the extent the ply or belt material is exposed

How to Interpret a CSA Tire Score

When the CSA calculates scores on vehicles, tires fall under “Vehicle Maintenance” on the BASICs (Behavior, Analysis, Safety Improvement Categories) assessment. Information is gathered from roadside inspections to develop scores, which are weighted depending on the types of violations found.

Tire violations carry some of the highest weight possible on the CSA scale, in which 8 is the highest:

8-point Tire Violations

• Flat tire
• Exposed fabric, ply, or belt material
• Tread or sidewall separation
• Audible air leak
• Cut that exposes ply or belt
• Poor tread depth

3-Point Tire Violations

• Re-grooved tires
• Tire load weight rating
• Under-inflated tires

Vehicle maintenance violations remain on the fleet’s record for 24 months and may affect the driver’s scores as well.

How to Decide Which Tires You Should Buy

Deciding which commercial tires to buy depends on a variety of conditions, including:

• Do you need soft or hard tires? Each offers different performance benefits depending on the type of truck.
• Will tires promote better fuel efficiency?
• What is the cost per mile on the tire? Is there a manufacturer’s warranty and if so, how long?
• What is the manufacturer’s reputation?

If you’re looking for commercial trailers for rent or purchase, you’ll want to consider the tires as well. Different types and sizes of trailers have different requirements that the trailer experts at Hale Trailer Brake & Wheel, Inc. can help you assess to make sure you get the right parts for your trailer.

The US Environmental Protection Agency (EPA) also offers a list of suggested tires and brands that are SmartWay approved for class 9, long-haul tractors and trailers.

Weather and Tire Choice

In addition to the factors mentioned above, weather plays a role in what type of tires are needed on a commercial truck or trailer. You want to think about what season it is, geographic region, road conditions, and terrain that may be encountered. Some conditions to consider are:

• Will there be snow and ice?
• Is rain common in the region?
• Will you be driving on rough roads with potholes, or need to drive in rougher terrain, like a dirt road?

You’ll also want to consider what your vehicle’s load rating is. Tires are marked with the maximum weight they can carry. Per DOT tire regulations, a vehicle should not operate if its weight exceeds that listed on the tires.

Steer tires are extremely important to the overall efficiency and safety of a commercial trailer. They take more wear from rubbing on curbs and affect the overall handling of the truck. Since they’re so important, you want to make sure that the steer tire you choose is high-quality so that it can withstand weather and road conditions over time.

Whether you’re looking for steer tires or general shoulder tires, durability is important. If you know rain and snow are a possibility, choosing a tire with deeper tread and the ability to resist cuts and curb damage will help you maintain good traction on slippery surfaces.

Where to Rent DOT-Compliant Commercial Trailers

If you have a fleet of commercial vehicles or are a driver, you’ll want to consider the unique needs for your freight and transport and how that affects your trailer choice. Hale Trailer Brake & Wheel, Inc. is the premier trailer company to help solve all your trailer equipment service and retail needs. Contact us to learn more about finding the right trailer/tire combination.