Heavy Truck Tire Failures Expert Article

Among the various types of mechanical failures that a commercial truck may experience, brake loss and tire failure are the two that are most likely to cause a crash. This article discusses the technical aspects of tire failures, and the responsibilities that CDL drivers and Motor Carrier have to inspect their tires to reduce the chance of a tire related crash.  

Tire Failures in Heavy Trucks

Commercial, medium-heavy duty tires are designed to support the higher loads seen in vehicles that are designed to haul cargo in the tens of thousands of pounds. A single commercial tire can support about two tons, or about the weight of a small car.

The largest contributor to a commercial tire’s ability to carry such heavy loads is its structure and the inflation pressure maintained, which can be more than three times the normal inflation pressure of a passenger car (up to 120 psi vs about 30-40 psi for a passenger car or light truck).

A passenger car or light truck radial tire relies upon polyester cords to provide the structural integrity necessary to carry a load. A commercial medium-heavy truck tire utilizes twisted steel cables in its structure and needed for the higher load capability of these tires. 

Certain configurations of commercial tires are capable of sharing loads of up to the 80,000 pounds of Gross Combined Vehicle Weight Rating (GCVWR) of a tractor trailer combination with up to 18 tires or more. A passenger car or light truck with only four tires is typically rated at 4,000 to 7,000 pounds GVWR. 

The perception that commercial tires are safe because they are stronger provides a false sense of security, because commercial tires are also subjected to higher stresses in a normal operating environment.  

Commercial Tire Blowouts

A commercial tire’s increased strength also makes them more dangerous when a blowout occurs and the higher inflation pressure is released almost instantaneously. A blowout is a direct result of a structural failure. 

Due to the size and height of the sidewall, blowouts to commercial steer tires can result in the immediate loss of steerability and control. The drag that is created by the blowout and the shift in ride height will typically pull the vehicle in the direction of the failed tire. The resulting yaw is difficult to recover from, creating a dangerous condition for the occupants of that vehicle and the other vehicles sharing the roadway.

Blowouts typically involve a tread separation. When performing an investigation of a tread separation, it is important to note if the tread separation resulted from the blowout, or whether the blowout followed the tread separation. 

Common Causes of Commercial Tire Blowouts

Causes of commercial tire blowouts can include:

• Underinflation/Overloading
• Punctures
• Improper Repairs
• Impact/Road Hazard
• Mounting Damage
• Excessive Speed
• Improper Application
• Manufacturing Defects

Some of the symptoms listed are controllable variables such as inflation, punctures, or improper repairs, and overall tire condition. These are generally identifiable by an inspection of a trained commercial driver during a pre-trip or post trip, visual/tactile inspection. 

Other forensic evidence may involve structural damage that would not have been evident during a reasonable visual inspection. The latter investigation would require a tire’s removal from the wheel to inspect it internally. 

Underinflation leads to tires operating in an overdeflected state. Overdeflection will generate higher than intended temperature exposure to a tires structure. Heat is any tire’s worst enemy, and tires are not self-healing. Once an area is affected, the injury can grow and lead to internal structure damage that can eventually lead to a blowout.

Forensic investigations of failed commercial tires involve identifying physical features consistent or inconsistent with known symptoms of failure and rely upon the investigator’s experience and background in identifying the physical evidence in a failed tire to identify rarer symptoms of a tire failure such as manufacturing defects.

Even with tighter federal safety and performance standards, commercial tires are not immune to manufacturing variation which may lead to defects and subsequent tire failure. 

Commercial Driver and Motor Carrier Responsibilities

Along with brake loss, tire failure can be one of a commercial driver's most terrifying and potentially life-threatening experiences.

While not all tire failures in commercial vehicles can be avoided, many can be avoided by drivers diligently conducting pre-trip and post-trip inspections, along with routine checks.

The Federal Motor Carrier Safety Regulations (FMCSRs) outline specific tire regulations. In addition to the general pre-trip requirements under 49 CFR 392.7(a), the driver must ensure that the tires and various other components are in safe operating condition before driving. Furthermore, 49 CFR 393.75 specifically addresses tire requirements.

Driver Responsibilities

Drivers must not operate the vehicle if any of the following conditions exist. If any are identified, drivers are expected to report to management and have the issues corrected.

• The steering axle tread depth must be at least 4/32 inch, while all other axles should have a depth of at least 2/32 inch. For accurate measurements, a tread depth gauge should be used in the major grooves at several points.
• Using a calibrated pressure gauge, check that all tires are inflated according to the manufacturer's specifications (the maximum cold inflation pressure is printed on the tire's sidewall). Underinflation can result in heat buildup and blowouts, while overinflation can lead to reduced traction and uneven wear.
• Carefully inspect the sidewalls and tread for cuts, cracks, or bulges, as well as for any exposed ply or cord and any separation in the tread or sidewall.
• Check for mismatched dual tires. Look for even wear and similar tread depths, and make sure no debris is present between the duals.
• Ensure that valve stems are free of cracks or leaks, and that valve caps are securely in place.
• While checking the tires, also examine the wheels and rims. Look for cracks, loose or missing lug nuts, and oil leaks from the hub.

Motor Carrier Responsibilities

Motor carriers have specific responsibilities under the FMCSRs concerning the maintenance, inspection, and safe condition of tires on their commercial vehicles.

Regulation 49 CFR 396.3 holds a motor carrier accountable for inspection, repair, maintenance, and consistently ensuring safe and proper conditions. It also prohibits a motor carrier from operating or allowing the vehicle to be operated if any tire is deemed unsafe and could likely lead to an accident or breakdown, and requires periodic inspections or replacements, and mandates that the maintenance and repair records be retained.

Failure to meet outlined standards of care may lead to out-of-service orders, enforcement actions from the Federal Motor Carrier Safety Administration, and potential litigation from negligence claims.

Trucking Operations, Vehicle Engineering, & Crash Reconstruction Expertise

Our investigations of tire failure incidents typically involve a review of all available documentation from the driver’s pre/post trip inspections, incident reports, and maintenance logs for the truck and trailer. Robson Forensic also employs vehicle engineering experts who understand the handling dynamics of heavy trucks and the physics required to accurately and dependably reconstruct collisions involving these massive vehicles.

For more information, submit an inquiry or call us at 800.813.6736.

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