Never Thought About What Is Inside

The common stick tire pressure gauge


While I have been using them for many, many years, I’ve never given much thought to the common commercial stick tire pressure gauges. That was until I read an article in a recent issue of “Commercial Fleet Tire Digest,” a monthly publication produced by Pressure Systems International, the manufacturer of the Meritor Tire Inflation System by PSI. The article described how this tool functions and provided some cautions, and I thought the information was worth sharing. The 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, explained the article. The spring pushes back and the calibrated rod (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. “A good gauge will have been calibrated properly and the pressure numbers marked appropriately at the factory to match the spring, said Pressure Systems International. “However, even a brand new reasonably priced gauge will only be accurate to +/-3 percent. Over time, this inaccuracy increases.” For instance, the spring constant or spring stiffness will change significantly based on the ambient temperature. “Most pressure gauges are calibrated at a room temperature of 68 degrees F,” wrote Pressure Systems International. “If you are checking tire pressures in the middle of winter and it is 20 degrees F, the spring stiffness will increase and any readings you take may be significantly lower by several psi or more. Conversely, when you do a tire survey in Phoenix during the summer, the spring stiffness decreases and the pressure results will be higher by several psi. Another factor affecting the accuracy of the stick tire pressure gauges is that this type of gauge gets dropped on hard surfaces and over time, the stick will not sit properly inside the spring causing additional error. There is also error associated with reading the correct number on the stick. The article concluded by noting: “Utilizing a master air gauge check station is the best way to verify stick gauges for accuracy. But you need to be aware that even a master gauge is only accurate to +/- 2 percent.”