The SmartWay Partnership has established protocols to evaluate the fuel-saving benefits of various devices. It provides information on a number of technologies—idle reduction technologies, low rolling resistance tire and, aerodynamic devices—that offer fuel-saving and/or emission-reducing benefits (epa.gov/smartway/technology/index.htm). It also has distributed information on other technologies that it has determined offer fuel savings, including automatic tire inflation systems.
Under-inflated tires flex excessively under load, producing heat and increasing rolling resistance, which wastes fuel. Tires inflated 10 PSI below recommended levels can reduce truck fuel economy up to 1%. In addition, stress from flexing causes fast and uneven wear, shortening the life of the tire. Add to that the fact that under-inflated tires tend to have more frequent punctures, which can lead to costly road service and loss of revenue. Goodyear studies have shown that a 15% under-inflation of steer, drive and trailer tires results in about an 8% drop in expected tread mileage and a 2.5% decrease in miles per gallon. Under-inflation is also detrimental to a tire’s potential for multiple retreads.
Despite such unnecessary costs, less than half of the over-the-road truck tires on our highways are within 5% of the recommended inflation pressure. Even with weekly pressure checks and a good maintenance program, it’s difficult to keep tires properly inflated. Because air can permeate through tires, even if the rim seal and valve stems are tight, they can loose up to 2 PSI each month.
Goodyear says, “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 under-inflation must never be allowed in over-the-road truck tires.”
Since the bulk of the load is carried in the trailer, a trailer tire under-inflated by 10 PSI can have twice the impact on truck fuel economy as the same amount of under-inflation in a drive tire. But trailer tire inflation pressures are difficult to monitor, since trailers are often away from a controlled service facility for extended periods of time. A fleet often doesn’t even own the trailers it hauls. Such circumstances place much of the responsibility for checking tire pressure onto drivers. However, according to SmartWay, only 8% of truck drivers check tire pressure with a tire gauge before each trip. Electronic tire pressure monitors, of course, will increase the likelihood of regular pressure maintenance by drivers, but certainly not guarantee it.
The next step is the use of automatic tire inflation (ATI) systems, which monitor and continually adjust the air pressure in tires, thereby maintaining proper tire inflation, even while the truck is moving. Such systems either use the vehicle’s own air-brake compressor to supply air to all the tires, or self-contained compressors mounted on each hub that are powered by the rolling motion of the wheels. Once an ATI system is installed, it should not require any special attention from the driver.
According to SmartWay, ATI systems can extend tire life by a minimum of 8%. They also eliminate the need to check tire pressure manually, saving time and labor while ensuring consistent proper tire inflation. For a typical long-haul combination truck, annual fuel savings could reach 100 gal. and eliminate one metric ton of greenhouse gas emissions. The cost of installing an ATI system in a line-haul truck is generally recouped quickly through fuel and maintenance cost savings. Truck fleets may realize additional savings from reducing the risk of expensive tire failure caused by under-inflation.