Is it OK to lubricate wheel studs and lug nuts?

 

Should you lubricate wheel nuts, or does this increase the risk of over-tightening?

 
 
 
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Lubricating wheel nuts: so hotly debated by armchair experts. The owners manual says: clean threads and no lube (in many cases). I say: definitely use lubricant on wheel nuts (actually on the studs).

Up front I am not telling you to do this. My default advice on everything related to your car is: don’t deviate from the owner’s manual.

What manufacturers are trying to avoid with their ‘no lube’ proclamation is a worst-case scenario - where someone lubricates the threads, and then some knucklehead uses an over-enthusiastic rattle gun on those same threads, over-tightening the nuts well beyond the boundaries of reason and common sense.

The lube increases the stretch of the thread for any given amount of applied torque. That makes sense, right?

There’s a limit to how far you can stretch those studs safely. Worst-case scenario: the stud over-torques, it yields (which is a point of no return separating the elastic deformation (temporary stretch) you want from plastic deformation (which is permanent distortion you definitely don’t want).

If a stud yields it no longer provides effective clamping force. This is bad - no doubt about it. Manufacturers acknowledge this risk by over-designing the studs. Massively over-designing them.

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Just doing a quick thought experiment here - I actually crunched the numbers. A common wheel stud size for cars is 12 millimetres. And I suspect they’re Grade 8.8 fasteners (that’s a common high-tensile category - not too brittle, reasonably tolerant of abuse, but no good for NASA, probably).

This is an educated guess about grade 8.8 because most carmakers specify about 100 Newton-metres assembly torque. And most bolt manufacturers specify 98 Newton-metres for M12 8.8 threads. QED, right? Carmakers have just rounded up for the spec in the manual. Five of these M12 8.8 studs will deliver 35.7 tonnes of clamping force between the wheel and the brake disc - absolute maximum, with all of the studs at the yield point. You don’t want to go there, but that’s the limit before bad shit starts to happen.

Read more at Wikipedia >>

100 Newton-metres on M12 8.8 gives you about 4.2 tonnes of clamping force per stud. Which is about 20.8 tonnes for the five, holding the wheel on. That’s only 58 per cent of the way to the yield point.

In other words, you’d have to stretch each stud 72 per cent more to get it to yield. A bit of anti-seize is simply not going to achieve that. It’s just not.

There’s a massive safety margin in play.

The case for lubricating the studs is: You get a flat tyre in the boonies and you can’t undo the damn lug nuts using the standard wrench that comes with the car...

...because A) - it’s repulsively inadequate, bordering on being a joke, and B) that over-enthusiastic rattle gun that may have been used to secure them? It’s no match for that.

For starters, I wouldn’t be letting anyone near my car for servicing or to replace the tyres, service the brakes, rotate the tyres - whatever - if they use a rattle gun. Forget it. If that’s your business’s wheel-installation protocol, take someone else’s money, because you’re not getting mine.

There’s a wheel nut torque specification in the owner’s manual. In every owner’s manual. I’d be referring to that, and I’d be ensuring anyone who puts their hands on my car uses a torque wrench.

For lube, you can use whatever you want, but the best stuff is probably that copper-based anti-seize compound. Which looks like grease with powdered coppery stuff in it. Principally because it’s made of grease with powdered coppery stuff in it. I’m sure it’s highly technical.

A little smear is all you need.

Get a torque wrench and some anti-seize. Every man needs a torque wrench. I’ve got three. A torque wrench and anti-seize is not a hot tub full of cheerleaders, but it’s somewhat close.

Read more at Wikipedia >>

Good for all kinds of things that you might have to undo one day. Like dancing nude on the boardroom table and waving your reproductive organs in the chairman’s wife’s face. A ‘command-Z’ button for life’s unfortunate slip-ups.

Another ace hedge against being stranded where the extras from Deliverance are all domiciled, with a flat tyre you cannot remove is: Get one of these and carry it in the car - a proper half-inch-drive breaker-bar with a four-inch extension and the right sized socket for your car.

Finally - take heart. There’s no road-going epidemic of wheels falling off in service, out there, in reality. This is purely because those studs are massively over-designed. On every car. Massively. They will certainly tolerate a little anti-seize - as long as you don’t also go nuts on them with the rattle gun from hell.

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