When wheel nuts come off a tractor, trailer or bus, the results are catastrophic since the loss of the wheel nuts leads to the detachment of the wheels from the vehicle.
When this occurs at high speeds, the threat to the driver, the cargo and other road users is significant. About this, there is no debate.
The core issue is to address the point of when the wheel nuts will come off. For commercial vehicles with standard wheel nuts installed, it is not a case of if the wheel nut will come off but when.
All wheel nuts, when installed on a new vehicle, are installed to a specified torque.
After the wheel installation, the wheel nut torque level should be rechecked after 50 to 100 miles of operation (and retightened if necessary to the recommended torque using the proper tightening sequence) according to TMC - Technology & Maintenance Council of American Trucking Associations.
All wheel nuts on all vehicles, new or old. It is past this point where the real debate of retorquing occurs.
The TMC go on to recommend that a torque check be made as part of a vehicles scheduled maintenance program or at 10,000-mile intervals. The key points here are:
Some companies (whether they admit it or not) do not service the vehicles as often as recommended and therefore retorque very infrequently.
Companies that follow recommended maintenance practices often do not include retorquing of the wheel nuts in order to save time and money.
Companies that do retorque the wheel nuts, often over torque the wheel nuts which actually shortens the life of the wheel studs through increased stress from the over torquing.
Even if you use a hand held torque wrench (and it clicks at the specified torque) it simply means that a minimum of that torque has been achieved. The wheel nut itself may still be severely over torqued. Over torquing is a very serious problem that can cause wheel studs to be stretched past their elastic limit.
Once the wheel studs have been stretched past their elastic limit, the result is proper torque readings from the torque wrench but no clamp load in the wheel studs securing the wheel to the vehicle.
All three of these scenarios lead to loose wheel nuts and the detachment of wheels.
The only remaining (and perfect world), scenario is the company that includes regular maintenance, which includes wheel nut retorquing with a calibrated hand held torque wrench. This, however, involves significant labor costs.
However, advancements in technology have led to the patented design of a wheel nut that requires no additional retorquing (subsequent to the initial retorque) while in service.
The Disc-Lock Safety Wheel nut for Hub Piloted wheels from Disc-Lock is maintenance free after it has been correctly installed and retorqued in accordance with TMC installation guidelines. After that no retorquing is required.
Disc-Lock produces maintenance free wheel nuts that are also self locking and so guaranteed to never come off as long as they are installed correctly.
The recommended torque for the most commonly used size (M22 X 1.5) is 500 – 550 Ft. Lbs. Disc-Lock Safety Wheel Nuts are also available in M18 X 1.5, M20 X 1.5, 3/4"-16UNF and 7/8”-14UNF.
Legislation in this arena of safety wheel nuts is slow to move but some public transportation, waste disposal companies, the US military (U.S. Army Tank-Automotive Command–TACOM) and other proactive and safety conscious companies are starting to move quickly.
The bottom line is that the technology is available at a low cost. The cost to retrofit an entire fleet is also far less than the cost of life (What is the cost of someone’s life?), cost of vehicle / property damage and the marred reputation of the company when wheel nuts loosen and wheel-offs occur.