Although there is a huge amount of anecdotal evidence for incidences of wheel loss and wheel nut loosening, there is little in the way of statistics. The 2007/08 Department for Transport sponsored study entitled 'Heavy Vehicle Wheel Detachment' estimated the typical annual frequency of these incidents in the UK to be as follows:
• Wheel fixing problems between 7,500 and 11,000
• Resulting in between 150 and 400 wheel detachments
• Of which 50 to 134 would result in damage-only accidents, 10 to 27 in injury accidents and three to seven in fatal accidents
Although this research is continuing with results published in Autumn 2008, one of its four initial recommendations is:
"Potential mandatory use of wheel nut retention devices or movement indicators, if independently shown to be effective"
Wheelsure's own independent market research also provides further evidence of how this problem impacts on fleet operators. In a survey conducted amongst 400 fleet operators:
• 83% of respondents had experienced wheel nut loosening at some time in their career
• 62% of respondents had experienced wheel loss in their career
• 32% of operators are concerned that despite their best efforts, wheel loss can still occur in their fleet
Fleet operators deal with the problem through maintenance regimes ranging in the most extreme cases from daily torquing regimes through to more orthodox service-based processes. Wheelsure's products offer an opportunity to manage fleets more confidently and in a manner that will reduce operational costs. However, in order to explain why this is true, it is necessary to understand the science that lies behind vibration wheel nut loosening.
Bolt science and the true cause of wheel loss
Wheel detachments are often described in the newspapers as "freak accidents". This reflects an everyday lack of awareness amongst the public that contrasts sharply with the research undertaken by Wheelsure amongst professionals in the industry. Wheel loss can be explained very simply by understanding the science that lies behind bolted joints.
The invisible problem: Clamp force and torque
Almost without exception, the wheel of a commercial vehicle is held in place by 6-10 bolts in an assembly known as the spigot or hub-mounted wheel. These bolts have been designed to deliver the correct amount of clamp force required to more than adequately hold that wheel in place when new. However, as the bolts age and degrade, the clamp force diminishes to a point where it is possibly insufficient to secure the wheel adequately. |
