The Compliance, Safety, Accountability (CSA) program for commercial trucks and buses from the U.S. Department of Transportation's Federal Motor Carrier Safety Administration measures carrier and driver safety performance under its Safety Measurement System (SMS).
SMS replaced the SafeStat system for identifying unsafe carriers through safety audits.
Under the CSA’s enforcement program, carriers and drivers are penalized for all violations under the program’s seven Behavioral Analysis and Safety Improvement Categories (BASIC). Tires fall under the Vehicle Maintenance BASIC.
One of the problems with the CSA program is that underinflated tires are considered a violation, yet there is no precise definition of exactly is an underinflated tire.
Consequently, underinflation is completely subjective for CSA compliance officers doing roadside vehicle inspections.
Creating a standard definition
In an effort to develop an industry standard for what an underinflated tire is, the Technology & Maintenance Council (TMC) has created a definition of an underinflated tire that it will submit to the Commercial Vehicle Safety Alliance (CVSA) for adoption.
This was announced at the TMC’s Fall Meeting and TMCSuperTech (National Technician Skills Competition) held Sept. 10 to 13 in Pittsburgh, PA.
TMC is North America’s premier technical society for truck equipment technology and maintenance professionals.
CSA compliance officers use the CVSA’s North American Standard Out-of-Service Criteria manual as a guide.
While the manual defines a flat tire - a tire that is 50 percent below the maximum tire pressure that is marked on the tire sidewall, or has noticeable (can be heard or felt) leak - it doesn’t specify what an underinflated tire is.
CVSA is an international, not-for-profit, voluntary organization comprised of local, state, provincial, territorial and federal officials from the U.S., Canada and Mexico that have responsibility for commercial vehicle safety operations and who perform vehicle inspections and conduct other safety related programs.
TMC’s recommended definition is that a tire is underinflated if its hot inflation is less than 70 percent of the maximum inflation pressure that is molded on the sidewall of a tire.
In other words, any tire with a hot inflation pressure above 70 percent is not underinflated.
A tire with an inflation pressure at less than 70 percent to 51 percent below the stated maximum inflation pressure on the sidewall is underinflated.
Tires inflated 50 percent or less of the maximum inflation pressure written on the sidewall should be considered flat.
For example, if the pressure written on the tire sidewall is 120 psi, it would be considered underinflated at 84 to 61 psi (70 to 51 percent of 120 psi).
TMC is also recommending to CVSA some guidance on where tire tread depth measurements should be taken. Here again, compliance officers have no guidance.
TMC is suggesting that such measurements be taken between two adjacent major tread ribs where there are no tread wear indicators, as measuring on an indicator will not provide a true measurement of tread depth.
Tread wear indicators are designated on the upper sidewall/shoulder of a tire.