Consider how much productivity road, water, and other maintenance crews lose when their truck loses a tire out in the field:
- Road service call = $250 to $350.
- New tire = up to $500.
- Lose a load, extend the time it takes to close out the work order, and have unhappy drivers and/or residents calling the office to complain.
Not exactly a warm and fuzzy moment fit for a Mastercard commercial.
No one can guarantee your vehicles will never have a flat, but if your shop maintains proper tire pressure you'll minimize the possibility of catastrophic tire failure.
Nothing But Air
As Harvey Brodsky, director of the Tire Retread & Repair Information Bureau likes to quip: “In real estate, it's location, location, location. With tires, it's inflation, inflation, inflation.”
Today's truck tires are sophisticated devices designed primarily to hold air. Tire components do two things: They keep the carefully engineered tread on the ground, and they keep air in the tire. The tread transfers forces to the ground for acceleration, braking, and cornering. The air supports the truck.
Air isn't just something to fill the tire. It's the reason the tire exists. Air is a critical, structural part of the truck.
Too much air, and tires become hard. They lose their ability to absorb shocks and to yield to rocks and objects that would cut, puncture, or abrade the tire. Excessive air pressure gives a harsh ride, damaging truck components and affecting driver comfort.
A few years ago, the Federal Motor Carrier Safety Administration (FMCSA) checked pressure on 4000 tires over several weeks and found more than 7% underinflated by 20 psi or more. Less than half were within 5 psi of their target pressures.
More than 19% of the tires in fleets of 50 or fewer vehicles were underinflated by 20 psi or more. In fleets of 3000 or more, only 2% of tires were underinflated. The difference is due to the more sophisticated maintenance practices of larger fleets, according to FMCSA.
When tire pressure is low, tread contact area elongates. That changes the rolling radius of the tire and increases the amount of flexing a tire experiences. Excessive flexing deteriorates fuel economy and destroys tires.
To illustrate, try flexing a paper clip. Move the wire back and forth and eventually it will break. If you touch the tips where it snaps, they'll be hot. A flexing tire can generate enough heat through internal friction to break wires in its steel cords and melt the rubber holding the tire together. That's why we see thrown treads littering the highways.
Many people think those are retreads, but if you look carefully, you'll see wire strands coming from the rubber on most of them. That's a sign that it was the carcass that failed, not the tread layer.
Gauging For Pressure
During pre-trip inspections, many drivers “thump” their tires to detect if one is low. Yet tests have demonstrated that at above 65 psi, it is almost impossible to tell if a tire is low just by sound. Shop personnel should gauge tires if drivers won't do it. One reason large fleets have far fewer underinflated tires is because dedicated yard and shop personnel gauge tires regularly.
There are devices to help check and maintain tire pressure:
- Dana's Central Tire Inflation System is a variation of a system the U.S. military uses. Pressure can be raised or lowered as needed to meet conditions: low pressure for low-speed, high-flotation locations such as a muddy jobsite; normal pressure for street use; high pressure for highways when fully loaded.
- Air pressure monitors from Doran, Tire Stamp, and other companies have sensors either strapped to the wheel or in the valve cap that transmit to dashboard-mounted displays and alert drivers when pressure is lost.
- A calibrated tire gauge. A gauge can be off by as much as 10% to 20% if dropped or handled carelessly. You can take your gauges to your tire dealer (if they don't have a way to calibrate gauges, find another dealer) or buy a calibration machine for your shop.
For fleets of 10 or more trucks, a $200 unit from ValvePal pays for itself with just one saved tire. Their Gauge Testing Station is pressurized with shop air, then the regulated output is zeroed electronically. Accuracy is within 1.5%.
Air pressure is critical to operating economy and tire life. So take the steps necessary to ensure tires are inflated to the proper psi to prevent those not-so-priceless moments from happening to your drivers.
— Paul Abelson is a former director of the Technology and Maintenance Council of the American Trucking Associations, a board member of Truck Writers of North America, and active in the Society of Automotive Engineers.