A closer look at the recommended practices

THE Trailer Safety Industry Coalition's initial effort was to develop a list of recommended practices for wheel mounting and application.

Aimed at vendors of components for the wheel assembly and at manufacturers of trailers and their transporters and dealers, they are recommended guidelines for the assembly of the fastening systems for aluminum and steel wheels. They were developed by TSIC's Technical Committee, approved by TSIC, and subsequently tweaked following meetings with NHTSA.

“It's fairly basic information, but it's information that not everybody has paid attention to in the past,” says Michael Kastner, the NTEA's director of government relations. “It's true in any motor vehicle, and it's particularly true on trailers the smaller they are.

“When you get a trailer new from a dealer, even if the wheels were mounted correctly, there's a break-in period. There's some loosening of the bolts, and they should be re-tightened correctly. A lot of users don't read that in the owner's manual or don't know how to do it. We're hoping we can get the information out to dealers to remind them to tell their customers that they play a role in this, too.”

Later this year, TSIC plans to initiate a testing program to learn more about the forces of clamping and torque, and the effects of paint, lubricants, and varying road conditions on those forces in the short and long term.

Here are the recommended practices:

  • COMPONENT GUIDELINES
    • Surfaces of contact on an aluminum wheel (the nut seat and the mounting surface) must be free of paint, contamination, and damage. Smooth, clean surfaces provide the most uniform clamping pressure and best retain torque.

    • Surfaces of contact on a steel wheel (the nut seat and the mounting surface) must be free of excessive paint, contamination, and damage. Smooth, clean surfaces provide the most uniform clamping pressure and best retain torque.

    • Surfaces of contact on the axle (the flat hub surface and the threaded studs) must be free of excessive paint, oils, grease, contamination, and physical damage.

    • Lug nut geometry must match that of the wheel nut seat. The threads and nut seat must be free of paint, oils, grease, and other contamination.

    • Stud length must be sufficient that, after mounting the wheel to the hub, the lug nut is engaged to a depth at least equivalent to the diameter of the stud. For example, a lug nut threaded on a ½” diameter stud should thread on for a depth of at least ½”.

  • ASSEMBLY GUIDELINES

    Assembly of the wheel onto the hub is a critical, safety-related process. The proper method of assembly and the consistency of the torque applied to the wheel fasteners are important factors in ensuring reliability of the fastening system and retention of the wheel to the trailer.

    The trailer manufacturer, distributor/dealer, and end user must consistently follow proper torquing technique in order to ensure the hub and wheel are properly seated and use caution to prevent anything from interfering with the flat, full designed mating contact of wheel mounting surface and hub. Excess paint, oil, and grease must be removed from the fastener contact surfaces (the mounting surfaces, studs, and lugs) or not applied at all. Adherence to the recommended “do's” and “don'ts” set out below will minimize the likelihood of faster torque loss and wheel separation.

  • DO'S:
    • Obtain confirmation from each component manufacturer that its component is appropriate for application, meets the appropriate component guidelines, and is compatible with the other components in the wheel system.

    • Develop and distribute a list or manual of proper assembly and torquing procedures consistent with these guidelines and specific technical information provided by component manufacturers.

    • Train appropriate personnel (factory and field) in proper assembly and torquing procedures.

    • Insist on consistent, strict adherence to these assembling and torquing procedures.

    • Conduct and document regular audits or checks to verify compliance with assembly and torquing procedures.

    • Investigate and correct any obstruction at the center bore of a wheel, resulting from a poor fit between the ornamental cap and the wheel.

    • Remove oil and grease from threaded fasteners (studs and lugs).

    • Mask or shield (cover) all fastener contact surfaces (mounting surfaces and studs) before painting axles, whether for improved cosmetics or for corrosion protection.

    • Only use an impact wrench with torque stick as a tool initially to lightly secure the wheel, applying a criss-cross or star pattern (see diagram).

    • Use a calibrated torque wrench to complete the torque-fastening process, applying the same criss-cross or star pattern.

    • Re-torque periodically during the trailer's initial towing and thereafter in accordance with the component suppliers' recommendations.

    • Maintain records of the maintenance and torque checks performed by transporters, noting any loss of torque or any corrective measures taken.

    • Investigate any customer claim involving wheel loss.

  • DON'TS:
    • Don't deviate from the component manufacturers' recommendations regarding compatible components without a competent engineering review.

    • Don't substitute any component for the components the suppliers have specified without a competent engineering review.

    • Don't deviate from the component suppliers' fastener torque specifications without a competent engineering review.

    • Don't use adhesive products to maintain fastener tension.

    • Don't use lubricants or oils on threaded fasteners (studs or lugs) to make applying the torque easier, unless assembly specifications require it.

    • Don't apply any additional paint on fastener contact surfaces (mounting surfaces/hub faces or studs).

These recommended practices are available at www.natm.com, www.rvia.org, www.nmma.org, or www.ntea.com.

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