Why Do Wheels Come Off Trucks?
October 2013, TruckingInfo.com - WebXclusive
Seasonality also appears to have been a factor, although hard conclusions about why remain elusive. Separation incidents reported in Ontario spiked to around 35 per month in January and February 1997 when the monthly average over the year was about 5 or 6. Fastener-related separation accounted for 25 of the recorded incidents while bearing related failures accounted for about 8 to 10. The following year, the seasonal increase was present, but with the heightened awareness of the problem, and after the training programs were in place, the numbers dropped to about half the previous year's numbers.
Drivers should be trained to inspect their wheels. Early detection can prevent a loose wheel from becoming a separation statistic.
In 643 incidents where the mode of failure was reported, failure of the wheel fasteners occurred in 65% of the incidents, while wheel bearings were the mode of failure in 26%.
Failure of the wheel itself or the axle spindle resulting in separations accounted for only 9% of the 643 incidents. Those types of failures are considered exceptions to the norm.
Of a group of 80 separation reports generated between 2000 and 2003 involving wheel fasteners, 66 or 83%, noted that the suspect wheel had recently been repaired. This turns out to be a critical observation.
One of Ontario's coroner's jury recommendations was a training and certification program for workers who remove or replace wheels on trucks, trailers and motor coaches. It's an offense in that province for a non-certified technician to install a wheel, and there is a sign-off procedure to document who did the work.
The training program covers, among many other things, proper wheel-nut torqueing procedures, which investigators had discovered was lacking in the province. Proper procedures include removing all rust and debris from mating surfaces, proper inspection of the fastening hardware and proper fastening, which means at the very least using a calibrated torque wrench rather than an impact wrench to tighten the lug nuts.
Investigations of many wheel-separations revealed that wheel nuts had worked lose due to lost clamping force attributed to material lodged between the wheel discs breaking free and/or fasteners damaged by over-torqueing. As we have noted, the number of reported separations has dropped since the training, certification and sign-off programs went into place. No longer, in Ontario, can just anyone grab an impact wrench go to town on a truck wheel.
The Ontario regulations also require a recently installed wheel to be retorqued after 50 to 100 miles. While many carriers and owner-operators say the requirement is burdensome, it appears to have contributed to a reduction in wheel separations.
Check out the October edition of Heavy Duty Trucking for more on the procedures and techniques for proper wheel-end maintenance.
You can read a very good synopsis of the events in Ontario in a report written by the Ontario Ministry of Transportation's Rob Monster. It's well worth 10 minutes of your time. You can down load it here.
Additional Wheel Separation Reports
Heavy Vehicle Wheel Separations: Exploring the Causes