Heavy Truck Tires: Their Various Roles and The Importance of Inspections


Expertise Includes:

    • Tractor Trailer Accidents
    • Vehicle Collision Reconstruction
    • Crash Data Retrieval
    • Forensic Mapping Technology
    • Motorcycle Collision Reconstruction

No one would argue that a tractor trailer is the same as an automobile (be it a truck, car, or SUV). The first thing that would come to mind is sheer size. Tractor trailers are larger in size and weight, and no doubt for good reason, these heavy trucks are designed to carry tens of thousands of pound of load.   An empty tractor with a semi-trailer comes in at around 35,000 lbs. A regular midsize car tips the scales at roughly 3,500 lbs.  Lots of parts of a tractor trailer are important, so to say this one or that one rates more important would be impossible (beyond the driver of course); however, a tractor trailer’s tires are definitely at the top of the list and regulations on heavy truck tires set the minimum standards on their acceptable conditions. Paying close attention to the tires during a tractor trailer post collision inspection can identify poor maintenance of the tires and ultimately the vehicle as a whole.

There are many differences between tractor trailers and cars. To be expected, tractor trailer tires are different and are held to a different standard, FMCSA standards! Tractor trailer tires are a team, working together to transport the load across the roadway. The tire’s location determines its function.  Because of this, there are different requirements for each tire’s position. Some tires are responsible for steering the truck. These tires translate the driver’s input into the tractor and ultimately the trailer’s direction of travel. Handling both longitudinal and lateral friction, they also tend to carry a larger portion of the weight with the truck’s engine poised on the front axle. These tires typically require higher pressure than the other tires. The next two axles of tires are responsible for propelling the truck and its load forward, but that’s not their only responsibility, they must also support the rear of the tractor and the front of the load. Lastly, the rear tires of the vehicle are responsible for supporting the rear of the trailer and its load. Again, there are typically two axles of four tires each.  Do not be misled, there are not two tires in one location so that if one fails the truck can keep on rolling to its destination. There are two because it takes that many to support the weight. Continuing on the lone tire after the failure of the first (for any more distance but to get off of the roadway) jeopardizes the safety of the truck, the load, and people. Because of the difference in their responsibilities compared to automobile tires, truck tires are designed differently and of a different compound. They have a different sidewall and a different tread composition. This can affect the way a tractor trailer relates to the roadway in how it stops during braking application versus how a car would respond in the same conditions.

Section 393.75 of the Federal Motor Carrier Safety Administration (FMCSA) Regulations addresses the importance of tractor trailer tire maintenance. It requires that the major grooves of a steering tire be no less than 4/32 of an inch.  Anywhere on the tire that major groove is less than this minimum is a violation. The other tires of the tractor trailer can go as low as 2/32 but the same rule applies. Nowhere on these tires can the major groove be less than 2/32 inch.

Tread wear below FMCSA minimums can come from many problems, such as flat spots from locked brakes. Just one area less than the minimum is a violation. One flat spotted tire beside one within specifications shows lack of attention.

Flat spots from poor brake adjustment and inattentive driving will cause the driver issues. No tire can have any visible body ply or belt material on the sidewall either. This sort of damage is typically from curb impacts, potholes, or other contact damage. There can be no tread or sidewall separation, no cuts that expose the body ply or belt material.

This steering tire is worn so that the outer major groove is barely visible and the belt material is worn through in several places. Far less than 4/32.

With the ability to recap truck tires, poor quality work or aged tires can have tread separations, while general roadway use (or in the case of pulpwood or other trucks that find themselves off road) tires come in contact with a spectrum of things that cause damage. A truck driver should regularly inspect the tires. The tire’s pressure must not be less that the tire’s rating on the sidewall. The tire pressure should be checked “cold” before the trip but can also be checked enroute and adjusted for the heat from traveling.

Possibly on it’s way to pick up it’s next load, this vehicle was observed traveling down the roadway with the inner tire’s tread visibly below standard.

Tractor trailers carry a lot of weight. Their size and weight needs to be under control whenever they travel across the roadways. Outfitting the vehicle with the proper tires for the job and maintaining those tires to the manufacturer’s and regulation standards help to ensure, as much as possible, that the trip can be done safely by keeping all 18 wheels on the road. Unacceptable tires found in a post-collision inspection can indicate issues of procrastination, lack of attention, and poor budgeting.  While it is expensive to outfit a tractor trailer with tires and to keep acceptable tires on it, the cost can be a lot worse if a tire fails from either poor condition or defect and contributes to a collision.

Aaron (Al) Duncan II, ACTAR, is a senior vehicle reconstructionist with Warren. Prior to joining Warren, he worked for 23 years as a South Carolina Highway Patrol Trooper to include 10 years as a Multi-Disciplinary Accident Investigation Team (M.A.I.T.) member. Al has investigated in excess of 1000 vehicle accidents and incidents, as a trooper. Al has testified multiple times in state courts and has been a court qualified as an expert in accident investigation and collision reconstruction. Al’s work expertise focuses on investigating and reconstructing vehicle collisions involving single and multi-vehicles, animals, pedestrians, motorcycles, heavy trucks and commercial vehicles. He is also a skilled user of forensic mapping technology and computerized collision diagramming software for collision scene analysis. Al has been trained in tractor trailer accident reconstruction by the Institute of Police Technology Management (IPTM) and is experienced in the data download and analysis of airbag black boxes (Crash Data Retrieval Units) in automobiles, pickup trucks and SUVs. He holds a Bachelor of Science Degree in Political Science from Lander University in Greenwood, South Carolina and completed the Law Enforcement Basic Program at the South Carolina Criminal Justice Academy in Columbia, South Carolina.

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