Spec'ing hubs for steel wheels

In order to keep prices down and profits up, some manufacturers take the easy way out and use the same hub for steel and aluminum hub-piloted wheel fitments. The bean counters of the world are already grumbling about the cost saving associated with the inventory reduction because a hub is a hub to them. But the problem is that this approach creates a few problems down the road that may affect the

In order to keep prices down and profits up, some manufacturers take the easy way out and use the same hub for steel and aluminum hub-piloted wheel fitments. The bean counters of the world are already grumbling about the cost saving associated with the inventory reduction because a hub is a hub to them. But the problem is that this approach creates a few problems down the road that may affect the life and performance of the wheel end assembly.

First of all, let's explain the situation. When aluminum wheels are installed on a tractor or trailer, there must be additional stud length to accommodate the increased thickness of the wheels. Likewise, the pilot-pads on the hub (which centers the wheels) must also be longer so they can support both wheels in a dual application. Using this same configuration for steel wheels works like a charm in the lab and on the factory floor, but there might be some long-term consequences.

It's hard to say which is more problematic in the field, the longer studs or the pilot-pads, so let's start with the studs. On a steel wheel application with aluminum length studs, more than an inch of thread protrudes beyond the outer edge of the flange nut. Threads are great collectors for dirt and grease so they are rarely clean when it comes time to remove the wheels. After retrieving a special deep-well impact socket, the technician applies a few thousand rpm to loosen the fastener. Even though I don't have any data to prove it, my guess is that continually dragging the flange nut over an inch of dirty threads at high speed doesn't help the performance of either the nut or the stud.

Which leads me to my next point, and that is the use of motor oil on hub-piloted wheels. Everyone agrees that a few drops of oil on the end of the stud plays an important role in generating the proper clamping force at the correct torque. When the drops of oil are more than an inch away from the position where the flange nut starts to create bolt tension, how much lubrication actually makes it to the bolted joint? I've never tested it, but it would be interesting to see how much clamping force is created when these common situations are regularly combined.

And while the longer studs collect dirt and grease, the longer pilot-pads become little corrosion platforms that usually make wheel removal a chore, especially on the inner positions. Steel wheels only need short pilot-pads. When there is another inch of pad extending beyond the wheel, the corrosion buildup makes a tight tolerance even tighter. In severe situations, the technician is forced to lie under the vehicle and physically hammer the inner wheel off the hub. Then, to combat the problem in the future, they apply a generous coating of anti-corrosive compound on the pilot-pads. This can potentially create additional clamping force issues if any excess material is squeezed between the wheel and the hub.

If the fleet runs aluminum wheels in every position, then none of this matters. If steel wheels are part of the system, however, then having the aluminum-length studs and pilot-pads will probably lead to some problems when steel wheels are serviced. Cleaning the components prior to removal may resolve some of the issues, but that still leaves some unanswered questions that are worth discussing.

Rather than come up with ways to make the longer studs and pilot-pads work better in steel wheel applications, wouldn't it make more sense to just use the proper length components in the first place?


Kevin Rohlwing can be reached at [email protected]

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