Tire maintenance, or the lack thereof, represents the greatest vehicle operating expense behind fuel. One aspect of tire care counts more than any other: proper air pressure.
According to the American Trucking Association, underinflation is responsible for about one road-service call per truck per year. The group estimates that improper inflation increases total operating costs by $600 to $800/truck annually.
Federal Motor Carrier Safety Regulations (FMCSR) place the responsibility for proper tire pressure on operators as part of the pre-trip inspection. While FMCSR 396.11 and 396.13 call for drivers to inspect tires and report defects, the law doesn't require measuring — much less recording — air pressure.
In the old days, drivers were instructed to identify low pressures by thumping them. But tests proved this method cannot identify low pressure if it's above 65 psi.
MONITORING FROM THE ROAD
The smaller the fleet, the greater the likelihood that tires are underinflated. This is because larger fleets typically use more sophisticated maintenance practices, according to FMCSR.
Many fleet managers install visual displays of mechanical devices to help during inspection. These basic tools include pressure equalizers for duals, and pressure gauges with visual warnings that alert drivers during pre-drive inspections.
The newest tire-pressure monitoring systems are electronic. They monitor, transmit, and display pressures continuously in the truck cab. Their sensors can be mounted on a tire valve assembly or strapped to the wheel inside the well.
Models that screw onto the valve like a cap monitor only pressure. Those that are placed inside the tire, either at the base of the valve or strapped on the wheel, can also monitor temperature. Some models can be patch-mounted on the inner liner, but because they often stay with the tires, they're not as popular as other devices.
Pressure should be taken with tires cold to ensure accurate readings because the air inside expands and pressure increases when tires are hot. Thus, some manufacturers offer temperature compensation software that adjusts readings to cold tire equivalent.
So far, the most sophisticated tire monitoring system on the market combines temperature and pressure sensing, temperature compensation, and telematics.