Wheel security: research reveals best practice 08 March 2010

Having read our feature on wheel security in the January 2010 issue of Transport Engineer, Mike Phoenix, of Mike Phoenix Consulting Engineers, wants transport engineers to benefit from a six-month study he carried out, as senior engineer for a major fleet insurance company.

Main background points to note, he says, include the following. First, steel, when it corrodes, expands between eight and 10 times – meaning that it's easy for 1m of soft, yet brittle, lumpy and uneven rust to 'grow' on mating faces, which, on a twin-wheel set-up means 4mm of potential play. Second, dirty, rusty and/or unlubricated wheel nuts and stud threads reduce clamping forces by 40—50%, due to friction loss.

Third, the driving force to the wheels should be transmitted by friction at the mating surfaces. Fourth, wheels fit on a central hub spigot, which controls centralisation. And fifth, wheel stud holes have a clearance of 4mm, so technicians should ensure that is maintained on fitting and tightening – otherwise the studs can drive the wheels, resulting in a potential for movement.

With those points understood, Phoenix reminds us of common findings with wheel detachments. Vehicles involved are generally older, well used and with big mileages. Wheels recovered often have elongated, polished fretting marks, where wheel nuts have rubbed on the wheel face. And wheel studs are usually heavily worn, where the wheel has battered against the studs.

Other main observations include that: where broken studs are recovered at incidents, some have nuts still attached; the mating faces are usually dirty or heavily corroded; studs are often stretched; and threads on studs and nuts are invariably dirty.

For Phoenix, the way forward is then about sound engineering practice. "First, check the nuts and studs for condition – and discard any suspect items," he says. "In fact, studs should be changed, maybe bi-annually. Then all stud and nut threads should be cleaned thoroughly, checked for absolutely free running, before lubricating with a 'super lubricant'. Next, all mating surfaces –wheels, brake drums, hub faces and centre spigots must be de-rusted and cleaned thoroughly, ensuring also that they are flat.

"Then, where brake drums are fitted, attention must be paid to the condition and security of the countersunk retaining screws, also ensuring that the heads are below the mating face of the drum. Those screws are essential: they not only secure the drum but also hold it in position to give correct clearance between the wheel studs and brake drum holes. And finally, the cleaned and checked wheels should be fitted, paying particular attention to maintaining the clearance between the studs and wheel holes to stop the studs driving the wheels, as opposed to friction between the clamped up faces."

As for practical tips, Phoenix suggests that, to maintain that all-important stud clearance, why not make up two tubes of appropriate ID and OD, so that you can fit and nip two pairs of opposing nuts first. Then, on torquing, he suggests that fitters mostly over-tighten, so you should check procedures in your workshop and institute changes where necessary – and that includes rethinking how much pneumatic nut runners are used.

Beyond that, kissing goodbye to detached wheel events is about proper regular checks and inspections – and not relying on wheel nut security indicators.

Author
Brian Tinham

Related Downloads
22926\Engineer_to_Engineer.pdf

This material is protected by MA Business copyright
See Terms and Conditions.
One-off usage is permitted but bulk copying is not.
For multiple copies contact the sales team.