TPMS for trucks: A look at band-mounted, valve cap and valve stem extension systems
While there are millions of vehicles on the road that have tire pressure monitoring systems, the same cannot be said for the commercial truck market. But that doesn’t mean they are not out there. In fact, a growing number of fleets are using tire pressure monitoring system (TPMS) technology to help lower their tire costs by warning drivers and/or maintenance personnel when a tire has insufficient air pressure.
At this point in time, any application of a TPMS in the truck tire market is purely voluntary since there are no federal regulations mandating it in vehicles over 10,000 pounds gross vehicle weight.
However, the National Highway Traffic Safety Administration (NHSTA) has been performing speed and endurance tests on truck tires and retreads over the past year or two. And while no official results have been released, preliminary reports have not been favorable in situations where tires and retreads are operated under-inflated. In all likelihood, these tests will lead to more stringent testing standards for new truck tires, and there is a strong possibility that retreads will be regulated in one way or another.
Improving safety is going to be the primary reason behind the changes. Of course, the technology is already there: it’s called an inflation gauge. But NHTSA makes a living by protecting motorists because we aren’t smart enough to protect ourselves. It’s not difficult to imagine future regulations for TPMS on commercial vehicles. Hopefully, the truck tire industry won’t be saddled with a non-standardized number of different systems that the retail tire segment must now navigate.
Speculation aside, there is a growing number of TPMS systems operating on tractors, trailers and motor-homes that can pull into any bay at any minute and create serious problems. Commercial tire technicians must know what to look for or they can easily damage components during service. Therefore, I’m going to focus on “live” TPMS systems that continuously measure inflation pressure during operation.
As it stands today, there are four types of sensors on commercial vehicles: band-mounted, valve cap, valve stem and valve stem extension. It’s important to note that many of these systems can be installed at the dealer level should customers request some form of tire pressure monitoring device.
SmarTire Systems Inc. offers band-mounted TPMS sensors. SmarTire’s SmartWave system contains sensors that are mounted with a stainless steel strap on each wheel. The sensors measure tire pressure and temperature every 12 seconds and then transmit the data to a wireless receiver every three to five minutes. If a sensor detects a pressure change of 3 psi, the regular schedule is broken so the sensor transmits data immediately. A display in the cab can be as simple as a warning light or as complex as an integrated unit that includes real-time data.
A unique feature of this band-mounted system is a break-away cradle for the sensor so any mistakes by a tech are not compounded by the high cost of replacing the whole sensor. Traditionally, band-mounted sensors are located either at the valve stem or directly opposite the valve stem, so techs should check both places after unseating the beads in order to locate the sensor.
If the sensor is positioned at the valve stem, then the demount process must begin at the valve stem for both the top and bottom beads. However, if the sensor is opposite the valve stem, then the demounting must also begin opposite the valve stem. The mounting process must begin opposite the sensor to ensure it isn’t damaged by the bead after it becomes positioned in the drop center of the rim.
Valve cap system
Perhaps one of the easiest truck TPMS systems to service is the PressurePro valve cap system from Doran Manufacturing LLC. To the outside observer, it couldn’t be any more simple because the valve cap is the sensor. But the first things techs must realize is that the valve cap sensors must be secured to the valve stems using special locks that require an allen wrench to remove. If you can’t seem to unscrew the cap, don’t run for a pair of locking pliers!
The other mistake that can be made with this system is the improper installation of the valve core. Doran has a special Dill Valve Tester that can be used to ensure that air pressure can be read by the sensor contained within the valve cap. When the tester is depressed in the valve stem, the tech should hear a strong hissing sound.
Passenger and light truck tire TPMS systems have traditionally utilized a valve stem sensor at the OE level. Some of them are easy to recognize because a metal stem with a collared nut is obviously different from the standard rubber snap-in valve stem. The same cannot be said for commercial truck TPMS that use a valve stem sensor.
Like any valve stem sensor, if it is removed from the rim for any reason, the rubber seal kit must be replaced or the chances of a leak increase. That means techs must be capable of demounting and mounting the tire while the stem is in place.
If you come across one without breaking it during the bead unseating process, all of the same principles apply to the position of the sensor during mounting and demounting.
Valve stem extension
The final type of TPMS hardware for commercial trucks that can cause problems for unsuspecting techs is the valve stem extension device. Mobile Awareness LLC offers such a device that contains a flexible hose extension for duals. The sensor is at the end of each extension so it rests next to the hub. This makes maintenance easier, so making sure of the seal between the valve stem and the extension is very important.
Additionally, the protection of the sensor during wheel removal is imperative. Sensors can be easily damaged if techs try to remove disc wheels without removing sensors from the hub. In some applications, the sensor and attaching bracket must be removed so the proper socket will need to be available. This can cause a problem in some road service applications, especially if the correct socket set isn’t on the truck.
By no means has this been a comprehensive look at TPMS for commercial trucks. I’m positive there are other systems out there that accomplish the same goals with a different approach. But these are the ones I’m aware of. As far as I can tell, there are no complicated recalibration procedures for any of these systems; all of the differences are based on physical application.
It also is important to note that our industry is at the mercy of drivers. If they fail to tell your tech that the vehicle has TPMS, they will still expect us to fix it if we break it. So the best approach is to embrace the technology and make sure everyone knows what to look for.
This article is part of an exclusive on-going series written for CTD by Kevin Rohlwing, senior vice president of education and technical services for the Tire Industry Association.