CSA and Tires

Addressing confusion on CSA policies for tire maintenance requirements.

When the Federal Motor Carrier Safety Administration (FMCSA) first rolled out its CSA (Compliance, Safety, Accountability) program in 2010, it was known as CSA (Comprehensive Safety Analysis) 2010. “2010” has subsequently been dropped and the program name changed.

A centerpiece of CSA is the new Safety Measurement System (SMS) methodology which is used to score carriers. The SMS organizes safety performance into seven Behavior Analysis and Safety Improvement Categories (BASICs): Unsafe Driving, Fatigued Driving, Driver Fitness, Controlled Substances/Alcohol, Vehicle Maintenance, Cargo-Related and Crash Indicator.

The methodology for the SMS, contained in a 123-page document, details and quantifies how the SMS score is calculated for each carrier.

The document, published by the FMCSA, can be downloaded at csa.fmcsa.dot.gov/about/basics.aspx.

The SMS score allows the enforcement community to identify specific safety problems for fleets, and will be used to continuously monitor on-road performance to determine whether a carrier’s safety performance has improved or if intervention is warranted.

Major Impacts

Tires, along with lights, are the two biggest issues facing fleets, based on the real-world results generated since CSA began.

Tires have a major impact on a fleet’s SMS score. With 18 or more tires on most Class 8 vehicles, the score can increase very rapidly for tire issues.

Tires fall under the Vehicle Maintenance BASICs category. The violations associated with tires can be found on pages A19 to A20 in the appendix of the aforementioned referenced SMS methodology document.

FMCSA has attached a violation severity number to be used in calculating the SMS score, depending on the specific tire issue. Tires carry either an “8” or a “3” severity rating, depending on the violation.

Violations that carry the “8” severity rating include:

  • Flat tire or fabric exposed.
  • Ply or belt material exposed.
  • Tread and/or sidewall separation.
  • Flat tire and/or audible air leak.
  • Cut exposing ply and/or belt material.
  • Steer tire tread depth less than 4/32 of an inch.
  • Drive, trailer or dolly tire tread depth less than 2/32 of an inch.

It is obvious that a walkaround vehicle inspection that includes tires should easily identify these high-severity violations. Tires which show cuts and exposed steel or fabric are not recommended to be running on your vehicles.

Tread Depth

Tires with tread depths below 4/32 of an inch for a steer tire and 2/32 of an inch for all other wheel positions have been in effect for just about forever. A simple tread depth gauge will identify low tread depth tires.

Since trailer tires tend to develop more irregular wear compared to tires on other wheel positions, the issue becomes where to measure the tread depth. This is not always obvious.

Highway inspectors need to understand that many tire designs have stone ejectors built into the bottom of the tread grooves. If the tread measurement hits a stone ejector, the measurement can be off 2/32 of an inch.

Air Leaks

A tire with an audible air leak must have a large puncture and this will lead to an eventual tire failure. Just looking at a tire on a vehicle will not determine if a tire is “flat.” The tire should be measured with a calibrated tire inflation gauge.

The Commercial Vehicle Safety Alliance (CVSA) considers a tire flat when the measured air pressure is less than 50 percent of the maximum tire pressure molded into the tire sidewall.

The current industry standard followed by most fleets in considering when a tire is flat and needs to be removed is 20 percent below the fleet air pressure specification.

Pressure Gauges

Accuracy of tire air pressure gauges is a big problem. Even brand new “stick” gauges right out of the box are only accurate to +/- 3 psi. A tire with 100 psi actual could be measured as 97 psi with one gauge and 103 psi with a second gauge.

As stick gauges age, the accuracy continues to drop dramatically. The inexpensive spring inside these gauges changes its stiffness properties over a combination of time and dropping the gauge onto hard surfaces.

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