Are You a 'Thumper'?

Despite the fact that tire inflation is one of the most important factors determining the life of a tire and ensuring optimum fuel economy, many drivers neglect their duty when it comes to regular checks of tire air pressure.

According to the Environmental Protection Agency's SmartWay Transportation Partnership, a recent survey of combination trucks found that less than half the tires surveyed were within 5 percent of the recommended inflation pressure. Another industry survey indicates only 8 percent of truck drivers check tire pressure with a tire gage before each trip.

One reason truckers may find it difficult to keep tires properly inflated is that truck tires can lose up to 2 psi each month, even if the rim seal and valve stems are tight. And a fleet may not be able to inspect or monitor its trailer tires regularly due to the fact that extended periods of time are spent away from service yards and because trailers are interchangeable. This places greater responsibility for checking tire pressure onto drivers.

Many drivers still rely on a highly unsophisticated and unreliable tool to check tire pressure, especially on inside duals the Tire Thumper, a wooden stick that resembles a Billy club. While they can't replace a tire gauge for accurately checking tire pressure, they can give an indication that the pressure between a pair of tandems is close. Whacking the tread of a tire with the device gives an audible thump, which changes pitch with the pressure in the tire.

Basically you are listening to the sound the thumper makes, and feeling way it reacts in your hand. A properly inflated tire will produce a sharper "thwack" sound when hit, and the thumper will bounce back sharply.

If a tire is significantly under-inflated, the sound will be more of a dull "thunk," and the thumper will not bounce back so well. But there are problems with this form of tire checking. If it's really cold, thumping won't even find a flat tire with certainty. And it's not a good way to tell if the tire is say 10 pounds low, but it will show if the tire is dramatically underinflated, say 50 pounds low.

And that's not good enough. According to Goodyear, proper inflation of radial truck tires is the most important maintenance practice to ensure long tire life. Once proper tire inflation has been determined, it should be maintained at that level as consistently as possible. "Loads carried may be increased/decreased for a given tire inflation when operating at reduced/increased speeds, but underinflation must NEVER be allowed in over-the-road truck tires," Goodyear states.

One way to prevent tire pressure underinflation is by the use of electronic tire pressure monitoring systems that signal to drivers when a tire becomes underinflated.

A more sophisticated method of ensuring proper tire pressure is use of automatic tire inflation (ATI) systems. ATIs monitor and continually adjust the level of pressurized air in tires, maintaining proper tire inflation automatically while the truck is in motion.

One ATI system uses the vehicle's own air-brake compressor to supply air to all the tires. Once an ATI system is installed, it should not require any special attention from the drivers. This eliminates the need to check tire pressure manually, which saves time and labor while ensuring consistent and proper inflation.

Savings and benefits ATI systems can not only extend tire life but truckers can also offer additional savings from reducing the risk of expensive tire failure caused by underinflation. Installing an ATI system on a truck's drive and trailer axles costs up to $800. However, for a typical long-haul combination truck, annual fuel savings could reach 100 gallons, saving $346 in fuel costs. Annual tire maintenance costs can also decrease.

The cost of installing an ATI system in a long-haul truck is generally recouped in just over two years through fuel and maintenance cost savings, according to SmartWay.

There is some evidence that loss of tire inflation pressure can be slowed by using nitrogen gas instead of air to inflate tires. While this method is not recommended as a substitute for regular checks of tire pressure, testing by the U.S. Department of Transportation has shown that nitrogen inflation reduces the rate of pressure loss.

There have been no scientific studies to document fuel savings obtained through the use of nitrogen inflation, but anecdotal reports indicate some fleets are seeing benefits from this approach, SmartWay says. One large national fleet reported to a panel of the National Academy of Sciences that it observed a 1 to 1.5 percent reduction in fuel use after using a nitrogen inflation system. Additionally, nitrogen inflation systems typically remove oxygen and water from the inflation gas; both oxygen and water can contribute to tire aging.

Paying close attention to inflation pressures and to tires that have run underinflated has never been more important, considering the potential for sidewall ruptures, the value of retreadable casings, the potential degradation of fuel economy and the cost of tire related downtime, Goodyear notes.

The tire industry recommends checking inflation pressures once each week on all tires with a calibrated tire gauge or a gauge that is checked periodically with a gauge known to be accurate. Thumping is not recommended!