Maintenance, load capacity drive design
They're still making them round. But that doesn't mean significant changes aren't taking place in truck wheel design. Although many of the changes may not be highly visible, they're helping fleets reduce maintenance and increase capacity.
The use of computer aided design, and specifically finite element analysis (FEA), makes it possible to change wheel designs on the computer "every hour rather than every six to eight months," points out Bill Noll, Accuride's vp of product development and technology. He explains that FEA allows manufacturers to optimize rim and disc design by taking "redundant" material out to reduce weight.
Alcoa also uses 3-D FEA models to "analyze wheels and determine anticipated stress levels," explains Matthew Brest, Alcoa's manager of design and computer aided engineering. By identifying low-stress areas, less material can be used in these spots and still maintain the wheel's integrity. Using these techniques, Alcoa's "new generation" hub-piloted wheels, which were introduced about four years ago, were designed to reduce the product's weight by about 8-10%.
Not all changes to wheels are out of view, however. For image-conscious fleets that want the look of aluminum without the higher price tag, Accuride has developed a styled, extra-service steel wheel that features hand-hole shapes that match aluminum wheels. Instead of the two or five hand-hole configuration of most steel wheels, this styled wheel has 10 hand-holes.
For many fleets, however, styling remains secondary to durability and appearance. To ensure that the new styled wheels maintain their appearance, Accuride uses a premium paint system. In addition to the standard "E-coat," styled wheels are given a top layer of powder paint. This finish adds to the durability of a wheel by protecting against corrosion. One measure a coating's durability is its ability to withstand the effects of salt spray. According to Accuride, lab tests have demonstrated a five- or six-fold increase in this characteristic in its premium coating.
Earlier this year Accuride introduced a low-profile 19.5- x 8.25-in. steel wheel for car haulers. The low-profile design decreases the weight of the wheel and increases the load rating, allowing fleets to increase cubic capacity and thus carry more cars and light trucks. A maximum load rating of 7,250 lb. allows the steer axle to be set further forward, reducing the need to distribute weight between steer and drive axles. The low-profile design also means vehicles can be loaded in delivery order rather than size order.
Alcoa's most recent entry into the commercial market is a family of wheels for extended-service, off-road applications such as mining and logging. The demands of these severe-duty environments are such that users are willing to give up a little weight savings in exchange for greater durability.
Last year Alcoa introduced a series of wide-base wheels for steer-axle applications. Again, use of FEA techniques enabled the company to design a wheel rim that provides additional clearance around the brake drum.
Innovative design techniques can also be used to address maintenance issues. For example, on hub-piloted systems, mounting and de-mounting can be made more difficult by a buildup of dirt and corrosion that causes the wheel to stick on. To compensate for this, Alcoa designed a groove into the bore of the wheel to reduce the contact area between the wheel and hub by about 50%, making the wheel easier to mount and de-mount.
In addition to their light weight, aluminum wheels offer a bright, shiny look that is appealing to some image-conscious fleets. To minimize the elbow grease needed to achieve this look, Alcoa developed a wheel-cleaning system that includes a cleaner, polish, and spray-on sealant. Fleets that can't put the time into polishing and buffing can choose a non-polished, satin-finish wheel.
Hayes Lemmerz makes both hub and stud-piloted steel wheels. The company has developed a special fastener for hub-piloted wheel systems, called the Hayes-L-Nut. This fastener is designed to better withstand the wheel loosening (torque loss) associated with contaminants, paint loss, and the normal seating-in process. Such torque loss can lead to wheel breakage and wheel-off conditions.
The Hayes-L-Nut system is composed of a series of Belleville washers integrated into the nut, making it similar to "an unloaded spring before torquing." The washers are said to act like springs to reduce the effects of torque loss from the normal seating-in process when paint, dirt, and metal-surface irregularities wear away.
