Recommended Practice Proposed RP 261 (T) VMRS 004-013-001 CONSIDERATIONS FOR AERODYNAMIC WHEEL COVERS PREFACE The following Recommended Practice is subject to the Disclaimer at the front of TMC s Recommended Maintenance Practices Manual. Users are urged to read the Disclaimer before considering adoption of any portion of this Recommended Practice. PURPOSE AND SCOPE This Recommended Practice (RP) describes important operational, inspection and maintenance considerations associated with the use of aerodynamic wheel covers in linehaul operations. It does not address the use of cosmetic hub cover caps. Introduction Many equipment users are seriously considering the use of aerodynamic wheel covers to improve the fuel economy of their commercial vehicles. While fleets in over-the-road, linehaul operations may realize fuel economy improvements thanks to aerodynamic wheel covers, they may also suffer negative impacts from these devices in other areas of their operations. Accordingly, fleet evaluation of aerodynamic wheel covers should include unintended negative consequences on operations and maintenance since the potential fuel savings could be offset by unexpected increases in miantenance and operational costs. Fleet/Operator Vehicle Inspections Vehicle inspections are an important first consideration when evaluating aerodynamic wheel cover use. Will a driver or technician be able to properly inspect the vehicle s wheel ends with aerodynamic wheel covers installed? Some wheel covers are clear/transparent and thus allow personnel to see through them for axle end inspection. However, such designs may not remain clear or transparent after placed into service. Wheel covers may also inhibit a technician's ability to clean the wheel surfaces of corrosive material. (See Figure 1.) Many wheel covers are solid/opaque/non-transparent (see Figure 2) and do not allow maintenance person- Figure 1 Figure 2 nel to inspect the wheel for: Loose and missing lug nuts Loose/missing/damaged studs Loose/damaged/cracked/corroded wheels Hub Seal/gasket/hub cap leakage Wheel cover and wheel cover attachment hardware damage Inflation pressure State/Roadside Vehicle Inspections Another thing to consider is how aerodynamic wheel covers will affect law enforcement inspectors since their inspections impact fleet CSA scores. At present, the Commercial Vehicle Safety Alliance s Proposed RP 261 (T) Ballot Version 1 Issued x/xxxx
(CVSA) policy is to not inspect or evaluate any truck part or component that inspectors cannot access by visual inspection without tools. Current CVSA vehicle inspections do not require that wheel covers be removed or accessible for the inspector. Therefore, if aerodynamic wheel covers are installed on an axle end, the inspector assumes that the components are in working order. If the inspector needs tools to remove the covers, then it is assumed that the end-of-wheel components are in satisfactory condition. However, CVSA and the Public Utilities Commission of Ohio (PUCO) both agree that the wheel end should have the ability to be inspected easily with a wheel cover installed and it is anticipated that CVSA will develop additional guidance on this topic in the near future. CVSA Inspectors will check the wheel end for the following out-of-service conditions as per CVSA's North American Standard Out of Service Criteria and Federal Motor Carrier Safety Regulations (FMCSR) 396.3 and 396.5: 1. Lock or Side Ring Bent, broken, cracked, improperly seated, sprung, or mismatched ring(s) 2. Rims for any circumferential crack 3. Disc wheels for any crack a. Exceeding three inches in length b. A crack extending between any two holes (hand-holes, stud holes, and center holes) c. Two or more cracks anywhere on the wheel 4. Bolt/Stud Holes (disc wheels) Any visible elongated bolt/stud hole 5. Spoke Wheel Cracks a. Two or more cracks more than one inch long across a spoke or hub section b. Two or more web areas with cracks 6. Tubeless Demountable Adapter Cracks a. A crack exceeding three inches b. Cracks at three or more spokes 7. Wheel Fasteners Loose, missing, broken, cracked, or stripped wheel fasteners that are ineffective as follows: a. Ten (10) fastener wheels three anywhere or two adjacent b. Eight fastener wheels or less two anywhere (applies to spoke and disc wheels) 8. Welds a. Any cracks in welds attaching disc wheel to rim b. Any crack in welds attaching tubeless demountable rim to adapter c. Any welded repair on any aluminum wheel d. Any welded repair other that disc to rim attachment on steel disc wheels 9. Hubs a. When any bearing (hub) cap, plug, or filler plug is missing or broken allowing an open view into hub assembly b. Lubricant is leaking from the hub and is present on the wheel surface (caused by a loose hub cap or hub cap bolts, hub cap damage) accompanied by evidence that further leakage will occur c. No visible or measurable amount of lubricant showing in the hub Tire and Wheel Maintenance Another consideration is the impact aerodynamic wheel covers may have on tire and wheel maintenance. If the aerodynamic wheel cover hides the wheel hand-holes and prevents access to tire valve stems, it must be removed before checking and adjusting tire inflation. If the covers must be removed, they should be able to be removed and reinstalled easily and quickly. Their attaching hardware should also be reusable and remain effective over multiple removals and installations, otherwise they may detach from the wheel end while enroute. Another issue when considering using aerodynamic wheel covers is their effect on wheel-end balance. If a wheel cover is selected for use, it should have no effect on wheel-end balance. Mounting Considerations Depending on how they are attached, aerodynamic wheel covers may raise mounting concerns with wheel end component manufacturers as there may be unintended wheel end issues. The quality of any wheel cover attaching hardware/mechanism must be considered to ensure the integrity of the wheel mounting system. There are multiple types of attachment systems, such as bracket mounting, wheel hand-hole attachments, wheel flange attachments and drop well, snap-in attachments. Some wheel covers are not designed to fit all types of wheels. If any wheel cover touches and rubs the wheel, contact the wheel supplier to determine if there are any potential problems. (see Figure 3). It should be noted that when using wheel Proposed RP 261 (T) Ballot Version 2
Figure 3 covers on steel or aluminum wheels, rubbing between the wheel cover and wheel may cause a loss of wheel coating, metal degradation, and premature corrosion. If two dissimilar bare metals are exposed and come into contact, it could cause galvanic corrosion which will make it difficult to remove the wheel cover. Contact the wheel cover manufacturer if these are potential concerns. A. Bracket Mounting Types Many wheel covers have brackets that use the existing wheel end hardware. When the brackets are positioned between the wheel nut and the wheel mounting surface, another joint is added to the system. It is important that this joint be kept clean and free of rust, corrosion, or other debris. Failure to keep this joint clean can result in loss of clamping force, loose wheels and wheel detachments. It is also vital to ensure that the bracket is made of a material that does not compress since that can result in a loose joint as well. Some brackets are designed to be installed under axle nuts. Like wheel covers that are positioned under wheel nuts, this adds an extra joint that must be kept clean. Axle nuts should be installed per TMC RP 656, Hub and Spoke Wheel Fastener Maintenance. Loose fasteners will induce axle flange or hub cap rotation which will then cause damage to the studs and the axle shaft. It is also vital to ensure that the bracket is made of a material that does not compress since that can result in a loose joint as well. There are also brackets that are designed to be installed under axle end cap bolts. (See Figure 4.) Failure to properly tighten the axle end cap bolts could cause oil to leak. This could cause the bearings to fail due to excessive friction and result in axle end detachments. Make sure that the axle end bolts Figure 4 are long enough for full thread engagement. When using this type of mounting system, 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 as well. Some aerodynamic wheel cover brackets are installed on the stud stand out after the nut is attached. When installing these brackets be sure that there is full thread engagement between the bracket and the bracket attaching nut to ensure the bracket stays attached to the wheel or axle stud. B. Hand-Hole Attachment Types Hand-holes can also be used to anchor wheel covers. (See Figure 5.) Ensure that the anchor does not damage the hand-hole in any way and that it is anchored tightly as road debris may damage the wheel cover mounting system. C. Flange Attachment Types Some aerodynamic wheel covers attach to the wheel flange. (See Figure 6.) It should be Proposed RP 261 (T) Ballot Version 3 Figure 5
increased axle lube temperature cavitation of lubricating fluid Figure 6 noted that the flange may not curl completely over the cover depending on the wheel design which is not designed specifically to anchor wheel covers. Consult the wheel cover manufacturer for mounting specifications. Wheel covers may also be attached with rim flange clamps similar to balance weights. When installing these clamps, inflation pressure must be removed from the tire to allow the clamp to slide between the wheel and the tire without damaging either one. These clamps may only be installed on the wheel once. Multiple attachments of these clamps may weaken the metal allowing them to detach from the wheel in service. Therefore, anytime the wheel cover is removed to check inflation pressure, inspect the wheel end, or perform other maintenance, new flange clamps must be used. See Figure 7 for additional illustrations of aerodynamic wheel covers. Wheel End Considerations Reduced air flow caused by using aerodynamic wheel covers may impact the operating temperature of the wheel end assembly. This does not usually create enough heat in the wheel end to damage tires and wheels. However, if there is another heat-generating component problem, wheel covers may mask and aggravate these problems. Possible effects from reduced air flow on wheel end components include: increased wheel end system operating temperature increased lining wear fade on drum brakes reduced bearing life rotor / drum distortion coefficient of expansion of hub nut and axle Proposed RP 261 (T) Ballot Version 4 Figure 7
However, according to data collected from fleets that use wheel covers and wheel manufacturer testing, wheel covers have no adverse effects on any of these components. Driver and Technician Training For sucessful deployment of aerodynamic wheel covers, appropriate personnel (e.g., technicians, drivers, and driver trainers) must be trained in their operation and maintenance. Training should include wheel cover installation and removal, the use of any special tools that are required, and how to read any visual indicators that advise if the covers are properly installed and locked. At a minimum, a training program should include the key points listed below (refer to the installation and maintenance guidelines provided by the wheel cover manufacturer for specific details): Explanation of why aerodynamic wheel covers are being used. Proper installation practices and maintenance procedures so technicians can install and maintain wheel covers correctly. Proper installation practices so drivers and technicians may recognize any irregularities. Determination of the additional time and tools required for drivers to remove and replace wheel covers during pre-trip inspections. Determination of the additional time and tools required for technicians to remove and replace wheel covers during tire/wheel maintenance. Special procedures required to access the wheel end for safety inspections and to check tire inflation pressures. Incorporation of a visual check of wheel covers during the driver walk around pre-trip inspection. Incorporation of an inspection of wheel covers into the fleet s regular Preventive Maintenance program. Procedures to determine and follow if the wheel cover and mounting hardware is damaged. Proposed RP 261 (T) Ballot Version 5