Project: Heavy Vehicle Wheel Detachment – Phase II
Last update: 26/04/2011 14:33:06
The aim of Phase II of this project was to build upon the work carried out in Phase I in order to recommend a standardised best practice for wheel tightening and maintenance. The effectiveness of the countermeasures identified in Phase I in terms of their ability to prevent wheel detachment, will also be evaluated.
There are four main objectives:
. Assess the ability of the various countermeasures, identified in previous research, to reduce the frequency of wheel nut loosening and wheel nut detachment and/or to reduce the severity of the consequences when it does occur.
. To assess the durability and practicality of the countermeasures identified to quantify the likelihood of measures that work in controlled conditions continuing to be effective in real world service.
. Standardisation of best practice for wheel tightening methods and maintenance.
. Update the cost benefit analysis of implementing the countermeasures throughout the UK heavy vehicle fleet (HGV and PSV).
Crowthorne House, Nine Mile Ride, Wokingham, Berkshire, RG40 3GA
+44 (0)1344 773131
Cost to the Department: £243,398.00
Actual start date: 01 June 2007
Actual completion date: 01 April 2010
Summary of results
- Heavy vehicle wheel detachment is relatively rare with respect to the very large distances travelled by such vehicles. However, when it does occur the consequences can be severe and the problem has been very well publicised for many years. TRL's research in Phase 1 of this project focussed on estimating the frequency of wheel fixing problems and identifying potential countermeasures to prevent or mitigate future problems. The project estimated there were between 7,500 and 11,000 cases of loose wheel nuts and between 150 and 400 wheel detachments resulting in 10 to 27 injury accidents and 3-7 fatal accidents each year in the UK. TRL's research also found that the causes of the problem were relatively well understood and there was considerable, if sometimes inconsistent, guidance on how to maintain wheel fixings.
Evidence from survey results suggested that maintenance guidelines were not always followed and there was evidence to suggest that those that failed to follow them had a higher incidence of wheel fixing problems. A range of solutions intended to tackle wheel nut loosening were identified.
This second phase of the project was again commissioned by the UK Department for Transport (DfT) and has built upon the 2006 research by TRL in order to identify best practice for wheel tightening and maintenance, and to assess the potential effectiveness of the identified countermeasures.
The second phase of the project involved a mathematical analysis of the clamp force required during normal driving, laboratory and vehicle-based tests to investigate various procedures for initial tightening and re-torquing. Accelerated wear tests were also completed to assess the effectiveness of the various countermeasures.
This is the final project report for Phase 2 of the project. It describes the methodologies and results from the tests undertaken during phase 2. The main conclusions from the study are:
1. The age, condition and level of lubrication applied to the mating surfaces and threads of standard wheel studs and nuts was found to affect the magnitude and consistency of clamp force generated during the tightening tests.
2. Tests also showed some evidence of substantial variation between individual studs/nuts with nominally the same specification. It is recommended that, if it is considered appropriate to do so, a review of BS AU 50 is undertaken to investigate any potential improvements to the magnitude and consistency of the clamp force generated could be achieved by amending the technical requirements to reduce variation in the material properties of wheel studs and nuts.
3. Standard OEM studs that had previously been used in normal service and the new locking devices tested during the tightening tests were found to generate a clamp force below the value required as part of BS AU 50, and below the value calculated as part of the mathematical analysis.
4. The tests to assess the relaxation and re-torquing methods showed that only a small percentage (<10%) of the initial clamp force was lost during the different test procedures. The results did, however, suggest that it is necessary for the vehicle to be driven, rather than left stationary, to induce the greatest loss in clamp force.
5. The Junkers tests showed that the various locking and retention devices offered some level of benefit over the standard OEM nuts alone by retaining a greater proportion of the initial clamp force.
6. During the Junkers tests the Visilok device maintained a high proportion of the initial clamp force but there was evidence that it had bound up on the threads and, in some cases, deformed during testing therefore this result is not considered representative of how the device was designed to work in real service.
7. Using accelerated wear tests with a test vehicle it was not possible, within the timescales of this project, to develop a test procedure, representative of real world service, which quickly and consistently caused standard OEM wheel nuts to loosen. Therefore it has not been possible to conclusively compare the real-world effectiveness of the different devices used in this project.
8. During one of the accelerated wear tests the clamp force for all 10 of the Disc-locks devices fitted to one wheel fell to zero within four days of the start of one particular test cycle. The standard OEM wheel nut and the other devices fitted to the vehicle at the same time also lost some clamp force but showed no sign of vibration loosening. The reason for this result is not known and could not be repeated when the nuts were re-tightened. It should be noted that configuration for this test was not in accordance with Disc-lock's recommended tightening procedure because they had been tightened to a lower torque to try and induce wheel nut loosening more quickly.
9. The vehicle tests indicated that maintenance of the wheel fixing joint is important because the vehicle tests undertaken without any artificial contamination maintained a greater proportion of the initial clamp force that similar tests with contaminations.