Retorquing the Lugnuts

Not necessarily, I mean maybe it's more likely that we'd find them to be overtorqued when checking out random wheels, but some of the crash data indicates that a lack of re-torquing has caused more fatalities.

"On October 23, 1992 the National Safety Transportation Board (NTSB) issued a Safety Bulletin H-92-102 as a direct result of a “spate of” five truck wheel runoff accidents across the country in which a total of seven people died. The bulletin recognized the following probable contributing factors for heavy truck commercial wheel separations:

1. Wheel separations involving broken studs, lugs or loose nuts most
frequently result from the improper tightening of the nuts or the failure to
retighten the nuts after initial seating of the fasteners.

2. Under torquing fasteners accounted for 65% of the wheel separations,
while 20% resulted from overtightening

3. Numerous sources identified the failure to follow proper maintenance
practices as the primary cause of improper tightening of wheel fasteners.

4. Maintenance manuals utilized by truck and wheel manuals used in the
industry were not uniform in content or presentation."

http://www.thefederation.org/documents/07.FDCC - Liability for Sudden Mechanical.pdf

 

You know, when something is done just to cya, that's usually because it has been known to happen, and isn't good. I think the only way to say how likely an event like this is would be to check the wheels. Otherwise flip a coin.

Still, it doesn't seem to be a common practice among drivers, because I'm special ordering most of this stuff (and am in a major trucking area, so it would be around if that were the case). I doubt most drivers are aware of this issue other than maybe getting a note on the paperwork to have wheels retorqued after service. It is recommended that they either do this themselves or have it done regularly, in all of the operator or service manuals I've come across. Yet I gather it would not be feasible to schedule on a regular basis, let alone the one retorque, unless I check this myself (especially if I want to go by the book). It's just odd to me how quick people are to second guess the recommendations of engineers, and they're basing this on confidence in engineering. On that note I hope they retorque all the nuts and bolts on bridges I drive over.

 

A couple of manufacturers looking to improve upon standard equipment discuss loosening of wheel nuts. To whatever extent this happens in practice, it seems to be testable and looks like normal wear and tear would be enough of a reason to double check them (kind of a background for what the tractor and trailer manuals say).

Loosening factors of wheel nuts:
Safe wheel assemblies rely on high clamp load. Loss of clamp load leads to movement between the clamped parts in the joint, and causes rotation of the wheel nut. The phenomena of loosening wheel nuts is a normal part of the everyday operation of heavy vehicles – caused by one or more of the following reasons.

• Poor road conditions
• Vibration
• Poor tightening technique or tools
• Joint relaxation
• Braking and acceleration
• Human errors during assembly
• Thermal expansion and contraction of wheel bolts
• Unbalanced wheels
• Increased vehicle speed
• Oil leakage from axle onto wheel nuts

http://www.nord-lock.com/wp-content/uploads/2012/05/NLWN_product-brochure_70095EN.pdf


Why Wheel loss occurs and how it affects the road transport industry

 

I was wondering about that, reading about how lubricating threads affects torque in general. Sounds like it is another distinction between hub and stud piloted wheels.

“Hub-piloted wheel systems (also called unimount) require motor oil on the studs and flange nuts,” says Rohlwing. “Motor oil is the only suggested wheel lubricant and it should only be applied to hub-piloted systems.”

To achieve the proper torque, it is important to use 30-weight oil and in the right quantity. Only a couple of drops are needed. “Using the correct torque and failing to apply oil to the stud and flange nut will result in insufficient clamping force, which leads to a wheel-off incident in most cases,” Rohlwing cautions.

On the other hand, the nuts and studs on stud mount wheels should never be lubricated. Snug up the nuts in the proper order and then torque the nuts in order to achieve the proper torque.

Tips to Prevent Wheel-off Incidents with Heavy Trucks

It's mentioned in another topic here also, Stud pilot vs. Hub pilot.

 

Well, there's more than 120 variations in tools, parts, and accessories for it. More than I expected, you haven't learned of anything new? I still have to try some of it out...

Don't worry though, I've spread my vastness of insight out among three topics to keep this one to a minimum (see also: When a wheel off occurrs... What do i need to change a wheel?).

 

Slowly but surely, I've been on the right track for inspecting threads while I wait for the wrench to get here...

Helpful hints about wheel stuff you really should know

"To check for loose wheels on vehicles, look for variations in the number of stud threads protruding beyond the nuts—that may indicate loose, backed-off wheel nuts.

Checking how far the stud extends past the nut is the easiest visual method to use for finding loose lug nuts, although only a torque wrench will provide you with a definitive answer."

 

Got this at least, it's pretty hefty at 10 inches long. Shouldn't be used much outdoors though, it says not to expose to extreme temps, humidity, direct sunlight, dust or sand, do not submerge...

Has its own case, including an adapter and procedure for checking calibration on a 3/4" torque wrench using a bench vise (the adapter socket has flat sides for that). I'm also going to test one of those 1:58 torque multiplers with it, got a 1-inch x 4-point socket for the other end, so I can reduce and turn it with a small torque wrench (found one on sale for $10, it's 20-200 in-lbs), I'm thinking around 100 in-lbs should do.

Entering the testing phase, stand by... wait, I don't have a bench vise yet (just an old mangled one, but this is precision work). I think the swivel head type with a pipe clamp on one end would work for locking a wheel bolt in place so I could torque on that too.

 

Reading more about the differences between hub and stud piloted wheels in the Motor Truck Engineering Handbook, it says hub piloted advantages include less nut/bolt wear, higher and more consistent clamping force, and improved torque retention, along with being easier to check or work on. Another book I found that touches on the topic, Truck and Trailer Systems, explains that hub piloted lug nuts are flat and the weight of the vehicle is carried between the center of the wheel and hub vs tapered stud piloted lug nuts with the studs bearing that weight, so those are getting worked loose and worn a bit more under load, by nature of their design. Torque on those should probably be checked most frequently.

Likewise, the "wheelsure" video which shows a hub piloted flange nut loosening as a machine vibrates the stud is kind of a mixture of the two systems, where studs would encounter more of that stress on stud piloted wheels, and the hub piloted nut would not likely get that much resistance without as much weight on the studs, as it is actually set up on the wheel.

Retorquing those is most pertinent shortly after the wheel is remounted (or when this having been done is in question), and if there's a noticeable difference in threads extending among nuts on a given wheel, as recommended.