Wheel security

A wheel is subject to a number of forces which act to loosen the wheel nuts.

If one of the wheel nuts loosens then these forces are distributed over the remaining nuts, which can cause the adjacent nuts to loosen as well. As more nuts become loose the process accelerates as the overall clamping force holding the wheel in place decreases.

When the clamping force reduces sufficiently the wheel will move on the hub. This results in side loading and further loosens the remaining nuts, which, if not spotted in time, leads to elongated stud holes, fatigue failure of studs, fretting cracks and in many cases wheel loss.

Loose wheel nuts can occur due to a number of reasons, including: under-torquing, over-torquing, incompatible parts, poor mating surface condition and through not following the manufacturer’s instructions.

Equipment

• Equipment used to fit wheels needs to be appropriate for the task and in a serviceable condition.
• Torque wrenches should be maintained and calibrated on a regular basis.

Transport operators

Operators should:

• Ensure drivers inspect tyres and wheels during pre-trip walk around inspections
• Ensure that after a wheel has been fitted the wheel nuts are rechecked for correct torque after a short period of in-service running
• Ensure that wheel nuts are checked for security and tightened
• Establish causes of wear and damage on loose nuts before re-tightening
• Ensure that manufacturer’s written instructions are followed by correctly trained persons and that comprehensive maintenance records are kept
• Consider fitting loose wheel nut indicators.

Maintenance workshops and mechanics

Maintenance workshops and mechanics should:

• Establish causes of wear and damage on loose nuts before retightening.
• Ensure removal and fitting of wheels are carried out to manufacturer’s instructions.
• Ensure all hub/drum and wheel mating surfaces are clean and allow a flush fit with the mounting surfaces of the wheel.
• Use the correct tightening sequence (wheel nut tightening procedures can vary for different types of wheels with different types of wheel nuts).
• Ensure nuts run freely over the whole length of the stud thread by hand.
• Use a calibrated torque wrench for the final tightening.
• Ensure that the wheel nuts are re-torqued after a short period of in-service running (between 50 to 100 kms is commonly recommended).
• Simply retighten nuts to the recommended torque when re-torquing (do not slacken and re-tighten).
• Ensure that manufacturer’s written instructions are followed by correctly trained persons and that comprehensive maintenance records are kept.

Certifiers

Heavy vehicle specialist certifiers should ensure that the requirements, which are in force in respect of wheel modifications, are complied with and that the operator has the relevant technical information.

Vehicle inspectors

Certificate of fitness (CoF) inspections include inspection requirements for wheels and wheel nuts. CoF inspectors should check the condition and security of wheels and wheel nuts and their associated components according to the requirements.