High among the ultimate nightmares of any fleet maintenance manager must be the loss of a wheel out on the highway that crashes into another vehicle — or a pedestrian or even an occupied dwelling — and hurts someone. A recent rash of wheel-loss incidents on southern Ontario highways has again focused attention on the care and maintenance of wheels and their fasteners.

To provide an overview on the current thinking regarding wheel security, Today’s Trucking interviewed Al Tucker, general manager of the Canadian Transportation Equipment Association and a longtime specialist in researching and promoting proper wheel maintenance.

“Wheel fasteners have definitely taken on a higher profile among drivers, fleet owners and maintenance staff,” he says. “For example, just look at how many torque wrenches have been sold — and many of them to people who’ve been in the truck-maintenance business for quite a long time, but never felt the need to own one before.

“The important thing, of course, is that they also be instructed in how to use that equipment properly — and not just for lug nuts on wheels,” he adds.

While the exact design of fastener (or flange nut, as they’re often called) will vary with the style of wheel being secured — spoked, stud-piloted disc or hub-piloted disc, and single-wheel or dual configuration– the basic system that a garage or fleet maintenance facility should employ to order, maintain and control these fasteners is universal, Tucker suggests.

“I’ve written-up what I call an ‘action plan for fastener control at the fleet level’, and I think the ten points contained therein can be usefully applied by just about any trucking operation,” he says.

The action plan’s recommendations are:

1.- Survey and identify the specific wheel or rim systems currently running on your fleet equipment.

2.- Identify the fasteners used on these systems and establish their identifying part numbers.

3.- Record these critical part numbers in your fleet records, and see that the information is in the hands of your parts-purchasing department.

4.- Always order fasteners by part number.

5.- If possible, try to deal with a maximum of just two certified fastener suppliers.

6.- Look for fastener identification markings, and make a note of them for future reference. Your mechanics should be aware of the importance you place on the use of certified fasteners.

7.- If your fastener supplier substitutes another part number for your original, he should be willing to provide you with written certification that the substitute fastener meets or exceeds the required specifications.

8.- As the fleet superintendent, ask your mechanics and tire mechanics to bring you a sample of any wheel-end fastener that has failed in service. This will let you confirm that no counterfeit fasteners have infiltrated your fleet, and will give you an opportunity to follow-up with your supplier in identifying the probable cause of failure.

9.- Make it a rule that, if wheel-end service is performed on your vehicle outside of your own shop, the provider of the service is familiar with the manufacturer’s recommended dismounting and mounting practices.

10.- Update your vehicle-specification records to ensure that new vehicles ordered for the fleet are equipped with wheel-end components that are compatible with your existing systems.

“There are millions of wheel nuts in use across North America, and that means a huge primary market and aftermarket,” Tucker notes. “Although I feel that, if properly inspected, cleaned and re-mounted, you can re-use a quality original-equipment flange nut probably two to five times following operations like tire changes or brake work, there are still many reasons why some wheel nuts will have to be replaced on tractors or trailers during the useful life of that vehicle.

“If we assume 60 wheel fasteners on a typical dual-drive-axle tractor, and 40 to 60 on a typical trailer, you can see the huge numbers that we’re talking about across the industry,” he goes on. “And, unfortunately, the value of that market has caused some suppliers to enter it over the years whose products — even ignoring the outright offshore counterfeits — were qualitatively not up to the necessary standard.”

That’s why Tucker has emphasized the importance of confirming the exact source and identity of the wheel nuts that your fleet has in use — whether the ones torqued onto your vehicles or those sitting in the parts bins back at the maintenance centre. Due to unscrupulous or simply inconsistent second-tier suppliers, you simply cannot safely assume that, qualitatively, “…a flange nut…is a flange nut…is a flange nut.”

Here’s a brief review of the types of wheels such fasteners are used with, and observations on how truck-wheel design has evolved:

Spoked wheels (typically in five- or six-spoke configurations) are usually cast from steel, and use a stud and clamp arrangement to secure a one-piece rim to the spokes. (A split-rim design was once common, but this was dangerous for tire-repair staff to work on.)

“Spoke wheels are still popular for some off-highway, high-axle-load applications,” Al Tucker observes, “but disc wheels — in steel or aluminum — are by far the preferred design these days. When radial tires came along for heavy trucks in the early 1970s, changes had to be made to the rim componentry of spoked wheels to accommodate them, and this caused problems.

“Spoke-wheel fasteners use a stud that’s threaded into each spoke-end, and there’s a flat hex nut that secures a clamp (which functions as a wedge to keep the rim tight). Trouble was, it’s very difficult to get each position wedged evenly, and then you’d get wheel wobble at highway speeds, and those expensive radial tires wouldn’t provide the benefit they were designed to offer.”

That spurred a switch to stud-piloted disc wheels, a design that — like the spoked wheel — had been around even back in the 1940s, but which ran truer, especially with radial tires.

Stud-piloted disc wheels are aligned on the hub via eight or (more commonly) ten studs. Apart from steer-axle applications, they are almost always employed in dual-wheel arrangements, with the inner wheel dished inwards over the brake drum and secured to each stud by a sleeve nut known as the ‘inner wheel nut’. The outer wheel is dished outwards, and is secured by outer wheel nuts (or ‘cap nuts’) to the inner wheel nut, but not directly to the stud.

That critical inner wheel nut — a sleeve nut with a small, squared end that requires precise torquing at values of up to 500 ft/lb with a special socket — is what holds the dual-wheel assembly onto the axle end, not the outer cap nuts. Since the outer wheel is connected only to the inner wheel, and not directly to the studs, the safety shortcomings of the stud-piloted (or ‘double-cap-nut’) design can readily be appreciated.

“Stud-piloted wheels are also maintenance-sensitive generally,” Tucker points out, “and if you don’t provide the required degree of inspection and maintenance, you’ll get cracks in the wheel disc itself, bolt-hole wear, and other headaches. Some operators found they were only getting a two- or three-year life cycle out of those wheels.”

Hub-piloted disc wheels were seen to be the answer. Although this design had been around for many years on buses and military vehicles in North America (and even longer in Europe), its adoption for commercial heavy trucks only dates from the early 1980s. By seating the wheel centrally on the hub, both wheels in a dual assembly can be secured by one flanged cap nut per stud, thereby eliminating the risks of that difficult-to-inspect inner wheel nut. Torque can be directly assessed by a driver on the road, using a bar wrench, and, if a stud breaks, the problem can be instantly recognized.

“Hub-piloted disc wheels aren’t perfect, but they’re a big step forward,” Tucker says. “And they’ve been improved over time, as well: the original design was called ‘full-piloted’, where the wheel contacted the hub around all 360 degrees, and you could get a corrosion-induced ‘freeze-up’ that ultimately made the wheel extremely difficult to remove. Now they use an ‘intermittent-piloted’ approach, with ‘piloting pads’ at three or four positions around the hub. This provides adequate piloting, but also facilitates wheel removal by mechanics.”

When it comes to the nitty-gritty of spec’ing wheel fasteners, however, the bottom line is that, in a sense…you can’t.

“If you spec a hub-piloted wheel system, you’ll get the fasteners that the vehicle manufacturer uses,” Al Tucker notes. “The two primary manufacturers of complete axle-end systems — hub, drum and wheel — are the Motor Wheel Company and Allied Signal, which has purchased the wheel operations of the Budd Company. However, neither of these firms actually makes their own fasteners; they use ‘Securex’-brand flange nuts made by the Illinois-based Metform Corporation.”

(Metform officials estimate their wheel-fastener products are found on about 95% of new trucks in North America, although offshore-fastener penetration is considerably higher for trailers, where purchase decisions are extremely price-sensitive.)

Tucker’s recommendation is that a fleet at least spec their new vehicles by specific wheel part number.

“I think, for the sake of parts control, it’s wise for fleet operators and owner-operators to be consistent in spec’ing the components they want,” he says. “And this can extend to wheels, hubs and drums.”

In addition to the ten points listed earlier, Tucker has a few concluding observations about dealing with wheel fasteners (primarily aimed at hub-piloted wheel systems):

* do not use air wrenches to fully torque-down the flange nuts. A half-inch-drive air gun may be acceptable to bring the nuts down to ‘finger-tight’ compression, but then switch over to a torque wrench for the last quarter-turn or so that provides the vital clamping force;

* always tighten the nuts in the sequence recommended by the manufacturer — don’t ever just go around clockwise, fully tightening each nut as you come to it;

* when re-mounting flange nuts, especially on trucks that run in corrosive environments like Canadian winters, put a couple drops of oil between the top of the hex nut and its crimped-on, rotating washer — but do not let any get on the other face of the washer (the side that comes in contact with the wheel);

* if a fastener doesn’t have any head marking, and preferably also some kind of symbol to identify the maker, don’t use that brand in your fleet;

* to the maximum extent possible, try to ensure that your replacement fasteners are the exact same product that came as original equipment on that vehicle. That’s your best way to avoid the confusion and danger of mismatched components.