In Focus: Wheels

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Aluminum wheels are good-looking, provide a better ride and save weight. Alcoa aluminum wheels can be spec’d with the company’s Dura-Bright finish (shown) for easy cleanup. Accuride offers Accu-Shield aluminum wheels for the same reason.

Spec’ing wheels requires only a few choices. Load capacity and offset are determined by vehicle OEMs, and departing from original values is not recommended. Insufficient load capacity poses an obvious safety hazard, but the danger of incorrect offset is less obvious. Offset is the distance between the axial center of the wheel and the mounting pad. Wheels with incorrect offset put unusual loads on wheel bearings, causing rapid wear and possible bearing failure and wheel loss.

When selecting wheels, one choice that’s much less of a factor today is the mounting system. Stud-piloted wheels use double cap nuts that mate with the ball-seats of the bolt holes to properly center the wheel on the hub. Hub-piloted wheels center the wheel on the hub, rather than on the studs, leaving the studs and lugs to provide clamping force only. This system generally is regarded as superior, and is used on the vast majority of vehicles.

Cast spoke wheels with demountable rims are another type of wheel usually not seen in over-the-road applications.

There has been a dramatic decline in the use of spoke wheels over the last 30 years, according to John Hall, Webb Wheel’s vice president of engineering. In the ’70s, an estimated 80 percent of heavy duty truck and trailer wheel ends were spokes, but today it’s probably in the neighborhood of 10 percent spokes vs. 90 percent disc wheels, he adds.

“The largest users of spokes today on Class 8 vehicles are extremely heavy-duty vocational fleets,” says Hall. “The use of spoke wheels has declined for the most part because of the weight differences and aesthetics as compared to disc wheel combinations. When they are used, it’s because the spoke wheel design inherently holds up in rugged applications better than a similarly-rated disc wheel.”

“Wheel choice should be based on how a vehicle will be used,” advises Mike Blacker, Accuride’s director, marketing. “If weight is important, a lightweight steel wheel or even an aluminum wheel might be best.” Reportedly, aluminum wheels can weigh up to 35 pounds less each than steel wheels, which could allow an additional 630 pounds of payload if used on all positions of a tractor-trailer.

“Polished aluminum wheels look great,” says Blacker, “but we have machine-finished aluminum wheels for use where appearance isn’t important, but weight is.”

“We think polished aluminum wheels are great for driver retention,” says Del Sauer, Midwest fleet territory manager, Alcoa. “They’re good-looking and provide a better ride.” That, he says, is because they’re lighter, so there’s less unsprung weight. And, because they’re a one-piece forging, they’re more true than steel assemblies, so vibration is kept to a minimum.

“Also, most people don’t realize how strong they are,” he continues. In Alcoa’s crush testing, “a steel disc wheel buckled two inches with 30,000 pounds of pressure. It took 157,000 pounds to do that to our aluminum wheel.”

A final word on steel wheels: Consider whether the vehicle will spend any time off-road. “In that case, you might go with a powdered top coat, which adds durability without much cost,” says Accuride’s Blacker. “It should look good for the life of the wheel.”

In short, wheel selection is really a matter of knowing what’s available, and knowing what you need your equipment to do.