But things are beginning to change now.
The first element of change is the Transportation Recall Enhancement, Accountability and Documentation (TREAD) Act, which is forcing at least the more sophisticated fleets to look at TPMS systems. Now the National Highway Traffic Safety Administration (NHTSA) is turning its attention to TPMS systems for commercial trucks and is expected to issue a notice of proposed rule making by 2007. Most people believe NHTSA will require some type of tire pressure monitoring solution for trucks.
Also, some types of systems have easily provable returns on investments (ROI) and have been around long enough to get the bugs out of their technologies. Tire pressure equalizers, originally introduced in the early 1980s, still find favor among truckers who want a simple solution to tire pressure monitoring and irregular tread wear.
Tire pressure equalizer systems constantly monitor tire pressure and equalize dual tire pressure by allowing air to transfer from one tire to another as they run down the road. A check valve connected to the valve stems with hoses opens to allow airflow between the tires but closes and shuts the air off in case of an instantaneous air loss, which prevents both tires from going flat.
In a slow leak situation, the valve isolates both tires after a pressure drop of approximately 10 psi. Since a central valve is located in these devices, a single airing point is provided that eliminates the need to remove the hoses to add air to the tires and makes airing the tires easier since both tires in the assembly are aired at the same time.
Users of these products see almost immediate improvement in irregular wear on their drive and trailing axle tires. Cupping, which is caused by a pressure differential between dual tires, is eliminated with equalizers. The equalizers also provide a visual indicator of air pressure conditions in the tires that can be seen from about 20 feet away. A driver doing his pre-trip inspection can easily see if his tires are good to go or not, thereby reducing enroute tire failures.
Some fleets using the new wide-base tires are installing equalizers to monitor pressure in these tires. They simply plug off one side and use it to check pressure during the pre-trip inspection. And these systems are relatively inexpensive-running around $60 per axle end. About 1 million Cat's Eye and Visualizer equalizers have been sold in the last 20 years.
Constant central tire inflation systems (CTIS) also are making inroads in the trucking industry. These systems take the air stored in the air brake tanks on a vehicle and use it to supply air to the tires to maintain tire pressure at a single, preset level.
Plumbed through the axle, they automatically sense the pressure in the tires and inflate as necessary when they lose air. Therefore, they eliminate the need to check tire pressure manually and allow a vehicle to remain in service despite small air leaks in one or more of its tires. Most of these systems are designed only for trailers at present and are usually installed at the factory when the trailer is built.
Users of CTIS have stated that the bugs in most of the systems now on the market have been worked out and that these systems pay for themselves if they eliminate just one emergency road call on the vehicle. These systems cost about $600-$700 per trailer and require virtually no maintenance.
One large fleet has found that enroute tire failures that used to run 40-50 a day have been reduced to 10 a day even though truck mileage has almost doubled. In addition, the company has gained 0.2 mpg in fuel economy. Tread mileage also has improved because cupping is a thing of the past due to CTIS maintaining the same pressure in all the trailer's tires.
Arvin Meritor's PSI inflation system has been installed on more than 500,000 trailers since it was introduced in 1994, and today the company dominates this market segment. However, now there are five manufacturers producing these systems, and with trailer builds way up this year due to the improved economy and the need to replace aging fleets, many fleets are spec'ing these systems on their new equipment. So expect the numbers of CTIS-equipped trailers to increase dramatically.
A ways to go
But since the early 1990s, the holy grail for fleets has been to have a tire pressure monitor system that provides temperature, pressure and mileage data, transmits that to the cab, the maintenance facility and/or the dispatcher via satellite and also provides the information the fleet needs to manage its tire assets better at little cost.
This information would help them determine what tires should and should not be retreaded, what wheel position they should be retreaded to, what their actual cost per mile is, what tires to buy, etc. TPMS systems for commercial truck tires are being developed to do these things, but none are all the way there yet.
There are three basic types of tire pressure monitors: valve stem mounted, wheel mounted and tire mounted. All of these systems monitor tire pressure through a device that senses the pressure and forwards a radio frequency signal to a display of some kind that is located in the tractor cab or in a more remote location. Many systems also monitor temperature and convert the actual hot tire pressure to cold pressure so that meaningful data is related to the user.
All of the systems on the market today are relatively new, and many are still in the process of working out the bugs. Fleet experience with them is extremely limited.
While many TPMS systems have the hardware to monitor tire pressure and temperature, they lack the software to convert this data into a useful tool for the fleet.
One company, TireStamp Inc., has taken a different approach to tire pressure monitoring. Instead of developing hardware, it has concentrated on developing a software solution that continuously collects tire and vehicle performance data from any integrated TPMS device. This data is pre-processed onboard the vehicle and transmitted off the vehicle utilizing the existing telematics communication method utilized by the fleet.
Several types of relevant reports are generated that help the fleet manage its tire assets. With fleet permission, retreaders could also access the database to determine a tire's mileage and heat history prior to retreading it.
TPMS systems are probably the greatest step in tire technology to come about since the low profile tire and will be the next big product commercial tire dealers will have to sell and service.
We've come a long way from the first pneumatic tires, but the importance of maintaining inflation pressure has not changed. The way we do it, though, would spin the heads of those early inventors.