We have seen some compelling but anecdotal evidence suggesting that wheel-end tightness can affect fuel economy — sometimes significantly. Joel Morrow, head of research and development, Ploger Transportation, has posted on Facebook about his experience with wheel bearings. He claims that the difference between factory-tightened tractor and trailer wheel bearings and those adjusted to a slight preload condition with a special tool produced a before-and-after improvement of 1.4 mpg in testing done prior to last year’s Run on Less fuel economy challenge sponsored by NACFE (the North American Council on Freight Efficiency).
We are not aware of any testing on wheel-bearing adjustment done to prescribed standards, but Morrow says bearing adjustment on new vehicles straight from the factory is inconsistent.
“We just took delivery of 10 new [tractors], and on two out of the 10, every wheel-end on the truck was too tight,” he says. “Most of the trucks had one or two wheel-ends that were too tight. On two other tractors, all the wheel-ends were just fine. Trailers are even worse than tractors. It’s not uncommon among a group of new trailers to see half of the wheel-ends too tight regardless of the supplier. We’ve seen this condition on several different brands of wheel-end. There’s just no consistency in that adjustment.”
Morrow says the condition is associated with the pre-adjusted bearing and hub assemblies that use a spacer to maintain bearing tolerance following a prescribed tightening procedure with pre-determined torque values. He suspects there may be some calibration issues with the tools used to install wheel hubs at the factory.
Bryan Williams, ConMet’s vice president of engineering, adds, “Proper torque at the factory is critical to ensure the bearing adjustment is correct. If the torque applied was too high the bearings can be put into excessive pre-load, or if the torque was too low, the bearings can have excessive endplay. Both of which could affect fuel economy and the performance of the bearings over time. Typically, wheel bearings have very limited impact on rolling resistance, however many alternative factors, including but not limited to wheel seals, lube, environmental factors, and the installation process have a much more significant impact on the rolling resistance.”