Why Do Wheels Come Off Trucks?
October 2013, TruckingInfo.com - WebXclusive
It's fine to run the nuts on using an impact wrench, but final fastener torque must be measured with a calibrated torque wrench.
We don't hear many reports of wheel separations anymore, but that doesn't mean we have solved the problem. Reliable estimates suggest unplanned separations still occur at a rate of probably several per day. Exact numbers are hard to determine because many incidents go unreported.
"We do not have much information about wheel off incidents," says William Schaefer, director of Vehicle Programs at the Commercial Vehicle Safety Alliance. "A lost wheel may not be discovered immediately by the vehicle operator and then when it is, it is fixed, providing no record for enforcement or research efforts. Also, even when a wheel is involved in a crash - whether with another vehicle or with pedestrians or property - the driver may not know it has happened and tracking the vehicle down could be a challenging forensic exercise."
The October issue of Heavy Duty Trucking features a in-depth look at solutions to wheel separations, including tips on bearing installation and wheel fastener tightening and installation procedures. Because of the limited space in our printed publication, there was not a lot of room for a broader discussion of the problem. In this edition of our monthly Tire & Wheel newsletter, we take a deep-dive into the issue of wheel separations, including some very good background on the problem and some innovative research into its causes.
The last time wheel separations came under serious scrutiny in this country was 1992. Following a rash of wheel separations in the fall of 1991 that left seven people dead, an extensive National Transportation Safety Board investigation concluded that "…the leading causes of wheel separations from medium and heavy trucks are improper tightening of wheel fasteners and bearing failure; both are the result of inadequate maintenance."
A series of recommendations issued by the NTSB was followed up by industry, including the Truck Trailer Manufacturers Association, the Society of Automotive Engineers, the Technology and Maintenance Council of the American Trucking Associations and others. Suppliers came to the table with innovative products and guidelines aimed at improving wheel installation and reducing wheel-separation incidents.
The NTSB report, available here, dealt more with solutions than the causes. In fairness, since 1992, policies and procedures have been developed to mitigate the problem, and information on wheel-end maintenance is easy to find. The recurring problems seem to rest with industry's reluctance in put in place rigorous maintenance procedures.
A few years after the series of incidents that prompted the NTSB investigation, the Province of Ontario experienced a series of fatal wheel separation events. The tragedies that occurred in 1995 prompted an investigation into the causes of wheel separation, and do date, some of the best research on the problem has come from Ontario.
A coroner's inquest, convened in October of that year, put forward 31 recommendations concerning wheel maintenance and inspection, chains of responsibility and legal accountability. Among the results of the inquest was a contentious absolute liability offence with fines of up to $50,000 to the carrier and driver, regardless of why a wheel might have separated.
The recommendations also mandated official investigation of each reported incident. From that, Ontario learned a great deal about the causes and was able to reduce the number of wheel separations quite dramatically.
The number of reported incidents dropped from 215 in 1997 to just 99 in 1998, with an average of 75 incidents per year between 1999 and 2003 (the most recent year for which figures are readily available). This decrease has been sustained up to the present time, but countless more wheel separations went - and continue to go - unreported.
Trends in wheel separation
In its investigation, officials in the Province of Ontario came up with some interesting statistics on wheel separation incidents. Research revealed that separation incidents were about even between tractor and trailer, with trailers representing about 6% more incidents than trucks.