There are a variety of ways aerodynamic wheel cover products are mounted on the axle end. Depending upon how they are mounted, they may cause issues with wheels, tires and hubcaps.
Therefore, the manner in which wheel covers are mounted is of great importance when selecting a product.
These products use a variety of attachment systems that include mounting brackets, systems that attach to the wheel hand holes or wheel flanges and some that snap in the drop-well of the wheel. Be aware that some wheel covers are not designed to fit all wheels.
As a general rule, wheel covers should not touch and rub the wheel, since this may rub the wheel coating off, degrade the metal and cause premature corrosion. Remember, if two dissimilar bare metals come in contact, galvanic corrosion will develop that can freeze the wheel cover to the wheel.
There are four types of mounting bracket designs:
1. Installed under the wheel nuts;
2. Installed under the axle nuts;
3. Installed under the axle-end cap bolts; and
4. Installed on the studs after the wheel nuts are attached.
When brackets are installed under the nuts of any attaching system, another joint is added to the system.
This joint has to be kept clean and free of rust, paint and other debris, or the component "sandwich" will lose clamping force and you'll get loose wheels and wheel-offs if the bracket is under the wheel nuts; axle flange or hub cap rotation, which will cause damage to the studs and the axle shaft if the bracket is under the axle nuts; and oil leaks, bearing failures and axle-end detachments if the bracket is installed under the axle end cap bolts.
In all of these systems, it is vital to ensure that the bracket is made of a material that does not compress since that can result in a loose joint, and all of these bad things can happen.
For brackets that are installed on the stud standout after wheel nuts are attached, technicians must ensure that there is full thread engagement between the bracket and the bracket attaching nut; otherwise the bracket may slip off along with the wheel cover while the vehicle is rolling down the road.
Another type of bracket attaches to the wheel hand hole. It's important to ensure the anchor does not damage the hand hole and that it is secured tightly to withstand impacts of road debris that may damage the mounting system.
Other wheel covers attach to the wheel flange. As you know, wheel flanges were not designed specifically for holding wheel covers on.
The flanges of some wheels may not curl completely over the cover, and this mounting system may not be the best for these types of wheels. If the flange does not completely curl over the cover, the wheel cover will not be securely fastened to the wheel — and you know what happens next.
The last type of attachment system uses rim-flange clamps, similar to balance weights, to attach the wheel cover to the wheel.
Inflation pressure must be let out of the tire to enable the clamp to slide between the wheel and the tire without damaging either one, just like balance weights.
And just like balance weights, they can only be used once. If they are removed and reattached using the same clamps, the metal may weaken, and the covers can detach from the wheel en route.
So every time you remove the wheel cover to check pressure, inspect the wheel end or perform any other tire, wheel, brake or axle-end maintenance, new flange clamps must be installed.
Entering this study, the Tire & Wheel Study Group surmised that wheel covers would reduce air flow and lock operating heat into the axle end and damage axle-end components.
Members thought it would be possible that the effects of reduced air flow could increase brake lining wear and fade on drum brakes, reduce bearing life, distort brake rotors and drums, and affect the lubrication of the axle-end bearing.
However, it was discovered that according to fleets that had experience running aerodynamic wheel covers and wheel manufacturers that had tested them, wheel covers have no adverse effect on these components.
Having said this, though, if there is another heat-generating component problem, wheel covers may mask and aggravate these problems.
If you have commercial accounts that are considering using aerodynamic wheel covers, encourage them to run a fleet evaluation of the products they are considering.
The evaluation should uncover any unexpected increases in maintenance and operational costs that could offset the potential savings they provide in fuel economy.
If you have fleet clients that are running aerodynamic wheel covers, make sure your technicians know how to remove and reinstall them correctly, have the tools they need to do this work and know to recognize any irregularities in them.
Also, you should work out with your customers the procedures that should be followed if the wheel cover and/or mounting hardware are damaged. The more you know, the better equipped you'll be to reduce drag and turbulence in your tire service.
For more information about aerodynamic wheel covers, see TMC RP261 Considerations for Aerodynamic Wheel Covers.
Peggy can be reached via e-mail at [email protected].