It’s a scene played out countless times a day: A truck driver climbs into his cab and cranks his rig. While the big diesel is warming up, he reaches down behind the seat or into the storage space in the door and pulls out a heavy wooden club. He climbs out and walks around his rig, thumping each tire along the way to ensure they have the proper air pressure.
According to industry experts, he’s wasting his time.
“When I see a truck driver walking around thumping their tires, I tell them they might as well take that stick and whack the hood of their truck to see if it needs oil,” says Harvey Brodsky, managing director of the Retread Tire Association. “That’s how accurate a tire thumper is.”
William Estupinan, vice president of technical service for Giti Tire USA – which markets and sells GT Radial commercial tires in North America – is somewhat more generous discussing tire thumpers, but just as dubious as Brodsky.
“If you think you have a ‘well-calibrated’ ear, thumping the tires could possibly give you an idea of the difference in pressure between one tire and the other, but it will never tell you the actual air pressure,” he says. “And the typical sound of a tire at a particular pressure will be different if the tire is hotter.”
Furthermore, Estupinan says, it doesn’t take much variation from optimal pressure to produce serious problems. Consider:
“That’s not to mention factors like irregular wear, higher thermal and mechanical fatigue of the casing, lower retreadability and even premature failure,” Estupinan says.
So even if a thump is close, it’s not good enough to determine if a tire is inflated safely enough to carry a load. The only acceptable and reliable way to check tire pressure, Brodsky says, is by using a calibrated tire gauge at least once a week.
HOW TO USE A CALIBRATED GAUGE:
Getting in the habit of putting a gauge on a value stem can be a tough adjustment for busy truckers.
“Considering the old saying that time is money, the time saved by not inspecting the tires, about 20 to 30 minutes, with a gauge but rather with a thump will be more than lost in the monetary terms of irregular wear, reduced wear life and even losing the tire if the air loss is caused by a puncture,” Estupinan says.
Once a driver is in the habit of checking tire air pressure regularly, his next goal should be to determine the optimum pressure required for his operation.
Steer tire pressure is most critical, says Guy Walenga, Bridgestone/Firestone’s director of engineering for commercial products and technology. Walenga and Doug Jones of Michelin Americas Truck Tires offer these tips:
HOW TO ESTABLISH IDEAL PRESSURES
Affected trucks include model year 2008-2018 Freightliner Cascadia and Western Star 4700, 4900, 5700 and 6900 trucks. DTNA says after hard brake applications, the brake light pressure switch may not activate the brake lights with the light application of the brake pedal.