Every steel disc wheel has a coating to prevent corrosion. Engineers get testy when you call it paint—and for good reason. Modern steel wheel finishes are better than ever with electrostatic powder coatings available at the original equipment and aftermarket levels. When serviced and maintained properly, the finish will consistently outlive the finish on a painted steel wheel counterpart from decades ago. Similar advances in aluminum wheel finishes and coatings have improved the overall appearance of wheels when compared to earlier generations.
Years ago, I spent some time with a state trooper who was assigned to the commercial vehicle inspection unit in the Mid-Atlantic area. He said the condition of the wheels or rims was a major factor in determining if a vehicle was a candidate for a roadside inspection. With a limited amount of time per vehicle, he would look for the obvious tires, lights, and brakes, but the wheels would often be the catalyst for some unwanted inspection from enforcement officials.
Steel wheel rim and wheel reconditioning has become much more important in the industry over the past decade because of the Compliance, Safety, Accountability (CSA) program that holds carriers and drivers accountable for their role in safety. That same trooper commented on how CSA scores are flashing red lights on where to look. If the fleet has issues in a particular area, that’s where he would go first. Maintenance scores are an easy enough target without broadcasting the need for inspection by operating with wheels in poor condition. Image isn’t everything with CSA, but a clean appearance goes a long way toward avoiding costly violations when the vehicle appears to be in good shape.
Large carriers with mounted tire programs have packaged a reconditioned wheel in the price of a new truck tire or retread. The newly finished wheel with a brand-new valve stem and tire/retread is the perfect solution to avoid roadside inspection questions. Vehicle enforcement officers are looking for things that are out of place or not uniform. Matching treads on reconditioned wheels won’t get a second glance in most cases (that is, of course, if the CSA maintenance scores are relatively low). It’s definitely a best-practice approach to tire and wheel operations that delivers consistent results with minimal problems.
Unfortunately, some fleets take the appearance of the wheels too seriously, so they take it upon themselves to give everything a nice fresh coat of paint after servicing. When the paint is applied to the rim or disc surface, one negative would be that it makes the rim stamp unreadable. However, when the spray can gets pointed at the mounting surfaces of the disc or the studs and nuts, it can potentially lead to clamping force issues after the vehicle returns to service. The maximum allowable thickness for any steel wheel paint or coating is 3.5 mils. Anything thicker than that on a mating surface can experience joint settling as the wheel flexes under the load.
Modern wheel and rim reconditioning systems can control the amount of coating thickness. More important, the old coating is completely removed, so the so that coats are not stacked on top of one another. There are other quality controls in place, and the very nature of electrostatic powder coats makes it much easier to evenly apply than a can of glossy white. After the coating has been applied, the wheel is baked in an oven to complete the coating process. Paint must be uniformly applied and completely dry before installation. Any runs or heavy spots on the mating surfaces are likely causes for loose wheels, which make operator error a major factor when painting wheels.
When the studs and nuts are on the wrong end of a can of glossy white, the potential issues are magnified. The threads on the stud are not designed to be painted. Paint gets in the grooves at the bottom of each thread and creates additional friction as the nut is tightened. Some of it is going to end up between the nut and stud where bolt tension is created, so painted threads can have a negative effect on clamping force even when the correct torque is applied.
On hub-piloted wheel systems, the overspray around and between the studs and nuts creates additional issues. Every time more paint is applied, it builds up around the flange. If the wheel is not aligned so that the flanges match perfectly with the previous spots, the additional paint under the flanges may become another cause for lost clamping force with the proper torque. Any buildup of paint on a mating surface is going to have a negative effect on bolt tension.
What may seem like a solution to roadside inspection problems can actually create the conditions that lead to loose wheels. Wheel manufacturers are in complete agreement against painting wheels, rims, studs, and nuts. They explicitly warn against paint buildup while universally endorsing the maximum coating thickness of 3.5 mils. If the appearance of steel wheels is a priority or a concern, then the best options are to buy new wheels or select a vendor with a quality refinishing systems so the spray cans stay in the garage.
