Wheels are exposed to road de-icing chemicals, and therefore corrosion. It dulls and pits aluminum and can structurally damage steel wheels.
TORONTO, Ont. — Wheels do not require much maintenance, but they do suffer their share of problems. From the damage during tire service, to cracking and bending from daily wear and tear — and corrosion — your wheels are under constant attack. Recognizing that wheels won’t last forever is the first step in improving service life, followed by diligent inspections for wear and damage every time the wheels come off the truck.
Steel and aluminum wheels are equally susceptible to fastener-related damage such as elongated or distorted stud holes. This sort of damage is usually caused by fasteners that were under-torqued during installation and come loose over time. Loose fasteners, ironically, are often the result of improper wheel service procedures such as improper torqueing or failing to clean the mounting surfaces between the wheel and the hub. Loose paint, rust, dirt and other debris prevents a flush mount, and when that material eventually dislodges it will leave a gap between the hub mounting face and the wheel. Once there’s a gap, the fasteners can’t help but come loose.
“Technicians should always clean the mounting faces of the hubs and the wheels with a wire brush or an abrasive disc on an air tool,” advises Accuride Corporation field engineer Brandon Uzarek.
Once the surfaces are clean and free of foreign material, the fasteners should be properly torqued, using a drop of oil between the nut and the flange. Torque requirements are listed by wheel manufacturers, but are usually 450-500 lb-ft.
“A one-inch impact wrench is not a torque wrench,” Uzarek stresses. “Use a calibrated torque wrench to achieve the proper clamping force, and make sure the wheels are retorqued shortly after they are reinstalled, usually within 50-100 miles [80-160 km]. Hardly anyone does this, but it critical to preventing wheel damage and possible wheel separations.”
Some maintenance experts recommend recording any on-road tire service in the driver’s daily inspection reports, so the maintenance department has a record of work and a prompt to retorque the wheels at the earliest opportunity. Additionally, anytime a tractor or trailer comes into the shop for repair or service, the wheels should be routinely inspected and retorqued, says Darry Stuart, a fleet maintenance consultant and frequent moderator at the Fleet Talk and Fleet Forum sessions at ATA’s Technology and Maintenance Council meetings.
“If you use those lug-nut position indicators, it’s useful to know that if they have backed off by as little as one-quarter of an inch, you have lost about 150 lb-ft of torque on that lug nut,” Stuart offers.
Everyday wheel damage
Wheels can sustain damage in everyday operations from excessive heat or overloading. Cracking between the hand-hold holes in the wheel is a good indicator that the wheel has been overloaded, notes Brian Thomas, marketing communications manager at Arconic Wheel and Transportation Products (formerly Alcoa). “Cracks that extend from one bolt hole to another often stem from over-torqueing or excessive loads.”
Any wheel that has been subject to high temperatures, such as those associated with a dragging brake or a wheel-bearing failure should be removed and inspected — and probably scrapped. Heat can alter the molecular structure of the metal alloy, cautions Chris Putz, principal engineer in the commercial vehicle and military wheel products division of Maxion Wheels. “For that same reason, we caution against using a bake-off oven to remove old wheel finishes on steel wheels. Temperatures can exceed 1,200-1,500 degrees. It’s a neater process than shot blasting, but the heat can be damaging.”
Rim flange damage is less harmful to the wheel than to the tire. Sharp edges can damage the tire bead. It’s more common with aluminum wheels and it can be repaired if detected in time.
Wheels should also be inspected for physical damage, such as out-of-round conditions and bends from things like curb strikes. The simplest way to check, though it may not be the most accurate, is to simply roll it across a flat surface and listen for the dent, says Uzarek. “We recommend using a run-out gauge to identify deformities. Steel wheels have a tolerance of .003 inches, while aluminum wheels can go up to .007 out of round.”
The ATA’s Technology and Maintenance Council has several Recommended Practice documents related to wheel maintenance and out-of-service conditions, including RP 222C, User’s Guide to Wheels and Rims. And wheel manufacturers can supply all the criteria you need to determine wheel fitness.
The threat of wheel corrosion
Corrosion is probably the most common problem in truck wheels, particularly steel wheels. It’s a problem with aluminum wheels too, but to a lesser extent. It’s seen as a white powder on the surface of the wheel, and it causes polished wheels to become dull over time. “Look for corrosion around the valve stem,” says Thomas. “Once salt and road chemicals settle under the O-ring it starts eating away at the metal, and that can eventually compromise the wheel.”
Corrosion is a little more obvious on coated steel wheels. Even the smallest break in the coating will allow road chemicals to enter. Refinishing the wheel is the obvious solution, but there are limits to the number of times a wheel can be refinished. Corrosion eats away at the metal structure of the wheel, and if the metal becomes too thin it will have to be scrapped. Refinishing with a shot blaster will remove even more of the surface metal, possibly exacerbating the problem.
“If the DOT stamp and/or manufacturers’ marks are illegible, or the wheel is damaged, it should be scrapped,” says Putz. “There are minimum standards for metal thickness. If the corrosion has gone far enough, the wheel will have to come off.”
Last but not least, tires themselves may be damaging your wheels. Rim flange wear, more prevalent in aluminum wheels but still possible with steel wheels, is caused by the tire bead moving against the inside of the rim flange. Shifting cargo weight causes the walls of your tires to rub back and forth against the wheel flange, creating wear. After a while, the abrasion erodes the flange surface and causes sharp edges that damage the tires. It can also be caused by abrasive material such as sand collecting in the groove between the tire and the rim flange. Eventually it starts to wear away at the metal.
Arconic and Accuride both offer guides on how to repair the flange, provided the damage has not progressed too far. They each offer a gauge with a profile that shows the extent of the damage.
“Affected wheels should be repaired quickly as the sharp edges created by the wear can damage the tire bead too,” says Thomas. “You are most likely to find rim flange wear on steer and trailer tires, and if you find it on one wheel, it will be there on others.”
Accuride and Arconic both offer coatings or treatments they claim can mitigate rim flange wear (Accuride’s Accu-Flange and Arconic’s Dura-Flange Wear Protection). These are available on new wheels only. In the steel wheel space, premium coatings such as Maxion’s MaxCoat, which involves an undercoating of zinc-phosphate, followed by a mid-coat of epoxy electro-deposition primer and finally a premium topcoat, can improve wheels’ resistance to common maintenance problems. They are more expensive than standard offerings, but they will save cost and grief in the long run.