Do truck operators really need to perform a wheel retorque some short time after every wheel installation? The short answer is yes — unless you have a clearly defined wheel-installation procedure in place, coupled to a wheel-nut torque monitoring program.

In simple terms, unless a wheel is correctly installed on a hub — by the book, using fasteners of predictable performance — it’s anybody’s guess how much clamping force is actually imposed by the nut or whether the wheel is even properly seated on the hub.

It’s one thing when we’re talking about new wheels mounted on new hubs with new fasteners. It’s quite another when installing previously used wheels and fasteners on in-service equipment. The repeatability is not there, so you need a back-up plan: retorquing.

Common wisdom holds that recently serviced wheels should be retorqued somewhere between 50 and 100 miles after a wheel has been installed. That’s a great idea, but the follow-through can be impractical. 

In its most recent update to Recommended Practice 237, Torque Checking Guidelines for Hub-piloted Disc Wheels, 237C, the American Trucking Associations’ Technology & Maintenance Council suggests fleets can run the recently serviced truck on a minimum 5-mile drive with several turns to get the wheel(s) seated, and then check the torque. And retorque if necessary. There’s more on this below.

In the meantime, here are four reasons why you should never take wheel fastener torque for granted — plus one tip to ensure wheels stay properly torqued.  

1. Wheel Mating Surface Conditions Vary

Rusty or dirty mating surfaces between the wheel and the hub can cause sub-optimal contact between the two.

Loose paint, rust flakes, dirt and other debris on the face of the mounting surfaces can interfere with a flush mount. The trouble begins when that material eventually dislodges as the wheel revolves and is subject to different directional stresses. The missing material leaves a gap between the hub mounting face and the wheel.

Once there’s a gap, the clamping force is reduced, and the fasteners can't help but come loose.

“Technicians should always completely clean the mounting faces of the hubs and the wheels with a wire brush or an abrasive disc on an air tool,” advises Brandon Uzarek, product design engineer for Accuride Corp.

2. Fastener Condition Affects Clamping Force

Fasteners that are rusty, stretched, or worn can cause unpredictable clamping force at each stud despite consistent torque application.

While there’s little published research on the impact of hardware aging and degradation caused by use and environmental factors, research by Ottawa, Ontario-based Woodrooffe and Associates suggests that re-using degraded flange nuts could be problematic.

“Anecdotal tests have shown that as [two-piece] flange nuts age, or when they are re-used, their torque/clamping force characteristics can be as little as 50% of the design value,” the company notes in its paper, Heavy Vehicle Wheel Separations: Exploring the Causes.

“Given that hub-piloted wheels depend exclusively on clamping force to prevent the wheel from separating from the hub, such a reduction in clamp force characteristics represents a significant risk to wheel separation," the report continued.

Technicians should check the condition of the studs with a thread pitch gauge before mounting the wheel. If the studs are in suitable condition, they should be thoroughly cleaned, deburred, and sparingly lubricated according to manufacturers’ recommendations.

Beware of fasteners of unknown origin, too. There’s a lot at stake with wheel fastening hardware. If the manufacturing pedigree isn’t known, its structural integrity will also be a mystery. Can you afford to take that chance?

3. Excessive Torque (or Not Enough) is Bad

Excessive torque applied by large pneumatic impact wrenches can stretch the studs, dramatically reducing their ability to maintain adequate clamping force.

Tighter is not better, especially when re-using studs and nuts. Many technicians attempt to achieve maximum clamping force by applying more than 500 lb-ft of torque without realizing the possible consequences.

“Torque is critical due to the fact the stud stretches like a spring,” says David Walters, manager of field service at Alcoa Wheel Products. “If the correct torque is not applied you will not get the correct clamp load.

“Thus, you could either under torque to have loose wheels or over torque and yield [stretch] the stud. Over-torque is the most common in the industry, and usually leads to reduced clamping force.”

Stretched studs will have deformed threads. If you lack a thread pitch gauge, check the condition of the stud by hand threading a new nut and observing any unusual resistance to hand turning. That could indicate stretching.

The generally accepted torque for a typical fastener used on a hub-piloted disc wheel (M22 x 1.5) is 400-500 lb-ft. But check your supplier’s torque recommendations if there’s any uncertainty.

4. Wheel Installation Procedures Are Inconsistent

Installation procedures, and adherence to those procedures, vary from shop to shop and technician to technician.

It’s nearly impossible to eliminate the inconsistency, so a backup procedure, such as retorqueing, is a good safety measure.

Jeremy Gough, director of national fleet maintenance at Canadian-based fleet Bison Transport, takes steps to ensure bearing and wheel installation is done right in the first place. He has a second technician check the work before the truck or trailer is released from the shop.

Bison also puts every technician involved in wheel-end work through a training program at least once a year. Drivers get similar training, but specific to what they can do to prevent wheels from coming off, he says.

“We take the threat of wheel separation seriously,” he says. “We use the pointer-type wheel-nut indicators that will show us if a nut is loosening off. And we check all the wheel fasteners on every truck that comes into the shop, even if it’s for a lighting issue. We check the nuts first, then fix the lights.”

Bison uses a calibrated pneumatic torque wrench from McCann, which Gough says cost about $8,000.

“We don’t cut corners on wheel maintenance and service,” he says. “It’s not cheap, but the money is better spent being proactive than reactive.”

Establish a Fleet-Specific Torque Check Interval

TMC has established a torque-monitoring procedure fleets can use to verify the effectiveness the installation program in lieu of the post-installation retorque. The process involves documenting the torque values at installation and then checking again following a trip around a pre-determined course under load.

“Through this process, the fleet can determine the level of integrity of its wheel installations and the torque loss that’s inherent in them," explains RP 237C. The RP also requires torque checks on at least 30 randomly selected wheels at regular intervals. Consult TMC’s RP 237C for details.

It still requires a bit of work and extra diligence, but logistically it would be easier and safer than relying on drivers to ensure wheels are retorqued after servicing.