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Wheel-offs: Tighter Is Not Better

Posted: August 1, 2014 by Rolf Lockwood

The first thing that’s obvious about wheel integrity is that there’s no shortage of information on the subject. Posters, pamphlets, simple one-page instruction sheets, a bunch of YouTube videos, not to mention mandatory day-long wheel-installation courses… you name it, we’re inundated with education and thus reasons why wheels should stay attached. Yet they don’t.

There are few credible statistics on the matter of wheel-off incidents, but those that do exist suggest that the trucking industry is getting better in prevention terms. Still, news reports of death by flying wheel aren’t entirely rare. What to do?

We’ll focus on fasteners in this article, though there’s just as much to be written about bearings, the other key source of wheel failures. And we’ll start with cleanliness.

Keep ‘Em Clean

There are many ways for a truck or trailer wheel to fail and come adrift. But even with a hub-piloted disc, the wheel that’s least sensitive to poor maintenance, the problem can very often be traced to simple cleanliness. The obvious cause of failure may be a loose fastener, usually due to a torquing problem during installation. But what created the lack of sufficient torque to hold things together in the first place?

Chances are, the wheel components were just plain dirty or rusty. And it doesn’t take much dirt or much rust to change things after a few thousand miles. The fact is that even a small amount of dirt or rust or something as small as excess paint drips between mating surfaces will cause a loss of clamping force over time. (Note that we didn’t say ‘can cause’ but ‘will cause’.)

It’s simple fact: if there’s any rust, dirt, excess paint, or even oil in the wrong place, your torque spec is out the window.

A common failure in disc wheels, for example, is a crack running between bolt holes around the wheel. Its likely causes are a loose wheel nut or worn mating surfaces. Dirt and corrosion will just make it worse.

Similarly, the crack that forms from the bolt hole to the center hole of a disc wheel is usually the result of loose inner cap nuts caused by foreign material between the wheel and the hub or drum. That crud prevents a flush contact, and it means the fastener never did manage to make things perfectly tight. Worse, it also means the fastener has been encouraged to loosen up.

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