Truck Tires and Gauges
By David A. Kolman
I’ve been using a stick truck tire gauge for as long as I’ve been trucking – and that’s a long time (never mind the exact number of years). However, I’ve never given much thought to what’s inside these gauges, or how they function. That is until I ran I into a chatty truck tire salesman. (Is there any other kind?)
He and I got to talking about the importance of regular tire pressure checks for getting the most life out of any tire. He agreed with me that the only true way to check a tire’s air pressure is to use a properly calibrated tire gauge. Kicking, banging or thumping a tire is not effective.
Early on in my trucking career, a heavy truck mechanic told me that trying to determine the air pressure inside a tire by banging on it is as effective as trying to check the level of motor oil in an engine by banging on the vehicle’s hood.
The tire salesman explained that a stick pressure gauge has a calibrated stick with numbers that fits inside a helical spring. When gauge is applied to the tire valve stem, pressurized air rushes in and pushes the piston to the right. The spring pushes back and the calibrated stick moves to the right.
When pressure is released, the piston moves back to the left but the measuring stick stays in place so the measurement can be read. He pointed out that the spring stiffness will change significantly based on the ambient temperature. For example, if you’re checking tire pressures in the winter when it is 20ºF outside, the spring stiffness will increase and any readings you take may be significantly lower by several psi or more. Conversely, if you’re checking pressure in Phoenix during the summer, the spring stiffness decreases and the pressure results will be higher by several psi.
I never realized that.
What I did know was that stick tire pressure gauges get dropped, which I assumed could affect the gauges accuracy. Indeed it does, I was told. Over time the stick will not sit properly inside the spring, causing additional error.
Thanks to a talkative salesman, I’m now wiser about the use and acre of stick truck tire gauges.