Preparation Is as Important as Force When Setting Torque on Truck Wheels

This story appears in the Nov. 3 print edition of Transport Topics.

Maintaining proper wheel torque requires a lot more than simply clamping down on lug nuts. Clean mounting surfaces and adequate lubrication on threads are just as vital for keeping trucks’ wheels rolling smooth and true, maintenance experts said.

“All the technician can measure is torque,” said J. David Walters, manager of the field service group for Alcoa Wheel Products. “That’s why all the fasteners must be properly prepared. If not, the technician has no idea of how much clamping force he has actually applied.”

Wheels with no excess paint and studs and fasteners that are free of rust and well-lubricated are elements that ensure adequate force is present, experts said. Rust, paint and worn fasteners create friction. And too much friction can lead to diminished pressure on the wheel, they said.

“If too much friction is in the equation, you get a false sense of torque,” Walters said.

According to Alcoa, a properly prepped wheel with all fasteners torqued to between 475 and 500 pound-feet will maintain in excess of 60,000 pounds of clamping force. But if excess friction is present, clamping force can be reduced to as low as 20,000 pounds. even at the full 500 pound-feet. of torque.

To ensure that proper force is maintained, start with a clean mounting surface, said Rafael Gonzalez, director of product management-wheels at Accuride Corp.

“Any combination of rust and wear will reduce clamping force, but rust is worse,” he said.

Once a wheel is removed, a good first step is cleaning the studs and nuts with a cleaning kit, said Steve Wilton, vice president of fleet solutions for Goodyear Commercial Tire and Service Centers. Most kits include a wire brush that installs on a drill and fits snugly around a stud to remove rust. Smaller brushes to clear away excess debris are also included, he said.

The technician can clean the inner diameter with the small brushes, and then run the wire brush up and down the entire length of every stud, said Kevin Rohlwing, senior VP of training at the Tire Industry Association.

This also is a good time to check wheels for chipped, flaking or thick paint, Walter said. “They must be free of excessive paint,” he said.

Problems can creep up if wheels have been hurriedly or thoughtlessly painted. “Painting steel wheels over old debris is a problem,” Gonzalez said.

He and Walters agreed that wheels should be thoroughly cleaned before being painted. And they should be painted with care. Paint thickness should be checked when painting is completed and must not exceed 3.5 millimeters, Gonzalez said.

And painted wheels should be periodically checked for chipping, since the clamping force of the wheel can cause paint to flake, Rohlwing said.

“On disc wheels, the most important areas to inspect are around and between the bolt holes,” he said, noting that a technician can properly mount a wheel that can still lose clamp load as excess paint squeezes out later.

To lessen the potential impact of paint problems, wheel fasteners and studs should be properly lubricated, the experts agreed. During installation, this will allow oil to flow between the flange and the hexagonal portions of the nut. Once torqueing has begun, the clearance goes away, making it difficult for a full coating of oil to be established.

“The flange must turn relative to the hexagonal portion of the nut when you torque it onto the wheel,” said Brian Bordner, of the Service Tire Truck Center outlet in Reading, Pennsylvania. “If it’s not oiled, the back of the flange turns on the wheel. That eats up torque and keeps the nut from developing clamp load.”

“Oiling is critical,” Walters added.

And it’s critical for both the studs and the fasteners, Bordner said.

“The studs dry out faster than the nuts,” he said. “Oil should also be applied to the pilot pads. There are four or five on the end of the axle. This will make it much easier to remove the wheel later.” Pilot pads are small, circular, metal surfaces around the circumference of the hub that support the wheel after it is installed.

An Accuride publication titled “Best Practice for Wheel Torque and Clamping Force” recommends two to three drops of SAE 30 weight motor oil or equivalent to the outer two threads of the stud, and a drop between the nut body and the flange. Those interviewed for this article agreed that straight-grade 30-weight oil is the best choice.

Walters spoke from experience about a failed trial of another product. “We experimented with anti-seize compound, but we could not get consistent results,” he said.

Consistency is also important when it comes to reinstalling wheels, as each step in the seemingly simple process is important to establishing proper clamping force.

Once the wheel is mounted on the truck, the first step is easing the nuts onto the studs.

“Start the nuts by hand,” Gonzalez said. “That way the tech can feel whether or not they are cross-threading.”

Walters said that if the technician can easily remove the nut by hand once it’s loose from the wheel, the nuts and studs are probably in good condition.

The next step, Gonzalez said, is to gently lower the truck so the tires just barely touch the ground. “Putting the truck down will then make it easier to apply torque without the wheel turning,” he said.

While it is common practice in many shops to do the preliminary tightening in a “crisscross” or “star” pattern, Walters said that is not necessary.

“You’ll be in pretty good shape if you simply tighten the top nut first and the bottom one second,” he said. “The critical part is to get the wheel seated.”

During a visit to Service Tire Truck Center, technicians were seen using half-inch air guns to snug up the nuts, which sped up the job without getting the fasteners too close to final torque. As long as the tools are rated well below the wheel’s final torque rating, they do a good job of getting nuts started on a stud, sources said.

But those interviewed for this article had universal agreement that more powerful 1-inch air guns should not be used, as the practice makes it impossible to determine the final torque and can overtorque the fasteners. They agreed that final torqueing must occur with an accurate, calibrated torque wrench.

And technicians must keep an eye on the fastener to make sure it is moving with the wrench.

“It has to be moving,” Walter said. “If it’s not, it could be well past 500 pound-feet and [the technician] has no idea what the final torque really is.”

The technician also won’t have an accurate measurement if the torque wrench is out of calibration, Rohlwing said.

“The most important factor is that the wrench is backed off every night so the spring mechanism does not lose tension,” he said. “Torque wrenches should be inspected daily and calibrated in accordance with the manufacturer’s specifications.”

Walters said, “There are many tools out there that can torque within the specs. Good tools are not cheap, but many different ones will do the job. I am a bigger fan of the dial torque wrench or a digital type. You see the number come up when you have exactly the right torque.”

Technicians also should avoid working too fast and potentially turning the wrench past the proper torque, he said. If the technician has any doubt, Walters said, he can simply check the studs.

“Check the number of threads beyond the nut on all of them,” he said. “If there consistently are

two to three threads, the wheel is seated. If they are uneven, you’ve got something caught in between.”

This might sound like a lot of trouble to technicians, but resorting to an impact wrench can cause bigger problems, Walters said.

“A stud is a spring,” he said. “When you torque the nut, it is actually telling you how much stress and stretch you have applied to the stud, which, of course, equals clamp load. But, a 1-inch air gun can easily produce [more than] 1,000 pound feet of torque. Most studs give way at 650 pound feet. You end up with stud breakage issues.”

Gonzalez said, “With too much air pressure on a 1-inch gun, and too much torque, you stretch the stud beyond yield, and then the clamping force is gone.”

And no job is complete without a road test. Once the wheels are mounted, the truck must be operated to allow for what the experts termed “joint settling.”

As the wheel moves around on the brake drum during driving, the wheel will settle and some torque will be lost. In general, wheels should be retorqued after 50 to 100 miles. In some cases, however, drivers won’t want to do the job or management believes they cannot be properly trained to do so. In these cases, Walters offers an option: Take the truck out for a 5-mile test drive, and then re-torque. The result is normally satisfactory, he said.

maintained, start with a clean mounting surface, said Rafael Gonzalez, director of product management-wheels at Accuride Corp.

“Any combination of rust and wear will reduce clamping force, but rust is worse,” he said.

Once a wheel is removed, a good first step is cleaning the studs and nuts with a cleaning kit, said Steve Wilton, vice president of fleet solutions for Goodyear Commercial Tire and Service Centers. Most kits include a wire brush that installs on a drill and fits snugly around a stud to remove rust. Smaller brushes to clear away excess debris are also included, he said.

The technician can clean the inner diameter with the small brushes, and then run the wire brush up and down the entire length of every stud, said Kevin Rohlwing, senior VP of training at the Tire Industry Association.

This also is a good time to check wheels for chipped, flaking or thick paint, Walter said. “They must be free of excessive paint,” he said.

Problems can creep up if wheels have been hurriedly or thoughtlessly painted. “Painting steel wheels over old debris is a problem,” Gonzalez said.

He and Walters agreed that wheels should be thoroughly cleaned before being painted. And they should be painted with care. Paint thickness should be checked when painting is completed and must not exceed 3.5 millimeters, Gonzalez said.

And painted wheels should be periodically checked for chipping, since the clamping force of the wheel can cause paint to flake, Rohlwing said.

“On disc wheels, the most important areas to inspect are around and between the bolt holes,” he said, noting that a technician can properly mount a wheel that can still lose clamp load as excess paint squeezes out later.

To lessen the potential impact of paint problems, wheel fasteners and studs should be properly lubricated, the experts agreed. During installation, this will allow oil to flow between the flange and the hexagonal portions of the nut. Once torqueing has begun, the clearance goes away, making it difficult for a full coating of oil to be established.

“The flange must turn relative to the hexagonal portion of the nut when you torque it onto the wheel,” said Brian Bordner, of the Service Tire Truck Center outlet in Reading, Pennsylvania. “If it’s not oiled, the back of the flange turns on the wheel. That eats up torque and keeps the nut from developing clamp load.”

“Oiling is critical,” Walters added.

And it’s critical for both the studs and the fasteners, Bordner said.

“The studs dry out faster than the nuts,” he said. “Oil should also be applied to the pilot pads. There are four or five on the end of the axle. This will make it much easier to remove the wheel later.” Pilot pads are small, circular, metal surfaces around the circumference of the hub that support the wheel after it is installed.

An Accuride publication titled “Best Practice for Wheel Torque and Clamping Force” recommends two to three drops of SAE 30 weight motor oil or equivalent to the outer two threads of the stud, and a drop between the nut body and the flange. Those interviewed for this article agreed that straight-grade 30-weight oil is the best choice.

Walters spoke from experience about a failed trial of another product. “We experimented with anti-seize compound, but we could not get consistent results,” he said.

Consistency is also important when it comes to reinstalling wheels, as each step in the seemingly simple process is important to establishing proper clamping force.

Once the wheel is mounted on the truck, the first step is easing the nuts onto the studs.

“Start the nuts by hand,” Gonzalez said. “That way the tech can feel whether or not they are cross-threading.”

Walters said that if the technician can easily remove the nut by hand once it’s loose from the wheel, the nuts and studs are probably in good condition.

The next step, Gonzalez said, is to gently lower the truck so the tires just barely touch the ground. “Putting the truck down will then make it easier to apply torque without the wheel turning,” he said.

While it is common practice in many shops to do the preliminary tightening in a “crisscross” or “star” pattern, Walters said that is not necessary.

“You’ll be in pretty good shape if you simply tighten the top nut first and the bottom one second,” he said. “The critical part is to get the wheel seated.”

During a visit to Service Tire Truck Center, technicians were seen using half-inch air guns to snug up the nuts, which sped up the job without getting the fasteners too close to final torque. As long as the tools are rated well below the wheel’s final torque rating, they do a good job of getting nuts started on a stud, sources said.

But those interviewed for this article had universal agreement that more powerful 1-inch air guns should not be used, as the practice makes it impossible to determine the final torque and can overtorque the fasteners. They agreed that final torqueing must occur with an accurate, calibrated torque wrench.

And technicians must keep an eye on the fastener to make sure it is moving with the wrench.

“It has to be moving,” Walter said. “If it’s not, it could be well past 500 pound-feet and [the technician] has no idea what the final torque really is.”

The technician also won’t have an accurate measurement if the torque wrench is out of calibration, Rohlwing said.

“The most important factor is that the wrench is backed off every night so the spring mechanism does not lose tension,” he said. “Torque wrenches should be inspected daily and calibrated in accordance with the manufacturer’s specifications.”

Walters said, “There are many tools out there that can torque within the specs. Good tools are not cheap, but many different ones will do the job. I am a bigger fan of the dial torque wrench or a digital type. You see the number come up when you have exactly the right torque.”

Technicians also should avoid working too fast and potentially turning the wrench past the proper torque, he said. If the technician has any doubt, Walters said, he can simply check the studs.

“Check the number of threads beyond the nut on all of them,” he said. “If there consistently are two to three threads, the wheel is seated. If they are uneven, you’ve got something caught in between.”

This might sound like a lot of trouble to technicians, but resorting to an impact wrench can cause bigger problems, Walters said.

“A stud is a spring,” he said. “When you torque the nut, it is actually telling you how much stress and stretch you have applied to the stud, which, of course, equals clamp load. But, a 1-inch air gun can easily produce [more than] 1,000 pound feet of torque. Most studs give way at 650 pound feet. You end up with stud breakage issues.”

Gonzalez said, “With too much air pressure on a 1-inch gun, and too much torque, you stretch the stud beyond yield, and then the clamping force is gone.”

And no job is complete without a road test. Once the wheels are mounted, the truck must be operated to allow for what the experts termed “joint settling.”

As the wheel moves around on the brake drum during driving, the wheel will settle and some torque will be lost. In general, wheels should be retorqued after 50 to 100 miles. In some cases, however, drivers won’t want to do the job or management believes they cannot be properly trained to do so. In these cases, Walters offers an option: Take the truck out for a 5-mile test drive, and then re-torque. The result is normally satisfactory, he said.