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[deleted] t1_j46nwig wrote

Reply to comment by die_kuestenwache in What does it mean to torque a screw to a specific torque? by alucemet

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lucidrage t1_j46rdko wrote

>You want to make sure the bolt doesn't encounter a resonance frequency, from the machine it's attached to, causing it to come loose.

Does this happen often with cars? Why do we have to retorque the tires 100km after changing it? Do they not tighten it after they swap it?

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davidm2232 t1_j46ryuj wrote

>Why do we have to retorque the tires 100km after changing it

I've found that is usually due to rust on the wheel/hub that crushes while driving. That being said, if the mating surfaces are clean and the lugs are tightened to the proper torque, they should be fine for thousands of miles/KMs

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hatsune_aru t1_j4a8m4q wrote

I've seen the paint on the mating surface of the lug nuts sometimes degrades and causes the nut to loosen.

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Different-Truth7668 t1_j46zobq wrote

Steel rims deform slightly, giving the connection some "springiness". But alloy wheels don't deform if you stay within the given torque range (if you don't, they crack) so any dirt particles, rust, sand etc. that grinds to dust after initial tightening will leave a gap between the hub and rim.

So forgetting retorque with steel rims is somewhat forgivable, but outright dangerous with alloy rims.

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davidm2232 t1_j470673 wrote

>but outright dangerous with alloy rims.

Not true at all. Mechanic/tire shops don't have every customer that had their wheels pulled off come back to have them retorqued. If they are torqued properly initially, no need to retorque.

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Different-Truth7668 t1_j474b8s wrote

For example, i forgot to retorque my alloys in the autumn when the mandatory winter tire months came on. When i finally did it, some of the bolts were already "finger tight".

Almost every garage i have worked at has reminded customers about retorque when they get their car back.

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[deleted] t1_j49ktq2 wrote

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spideywat t1_j49m0xk wrote

It has nothing to do with the torque value and everything to do with the material. I have had dozens of vehicles, driven hundreds. Aluminum rims often come loose. The nature of the material. I have torque wrenches and a big shop.

On one set of rims it takes about 15 minutes to torque each wheel the first time then a short drive and some of the nuts loosen. 2015 f350. The Ford diesel mechanic noted the same thing and he hates those rims too.

I was at a garage where the mechanic told the customers that retorquing was bull and he had never done it once in his life. He was a fool.

Wheels come off less often now then 30 years ago, after which they introduced retorquing tires.

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spideywat t1_j49mzcy wrote

We have put millions of kms on our vehicles. We know about them loosening, however, there will always be people saying it is nonsense or an error in the initial torque. Follow your pattern, set the proper torque, every once in a while some will loosen on their own. That’s why we have pre trip inspections and a ton of regulations on our vehicles.

And if you over tighten then you are weakening the studs and can ruin your threads. Ounce of prevention as they say.

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Coomb t1_j49xo5s wrote

Everything deforms when pressure is applied. Alloy wheels are actually considerably less stiff than steel so they will deform more under the same load.

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uwauwa t1_j46zwey wrote

its due to aluminum allow wheels, something about the softness of the metal "could" loosen after stress cycles.

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NiteShdw t1_j470fqu wrote

I’ve lost screws off my motorcycle because they vibrate out (small ones that hold on the fairings).

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hatsune_aru t1_j4a8rpg wrote

Motorcycles are subject to significantly more vibration, and some motorcycles are even designed such that the fasteners aren't guaranteed to not back out (in cars, they are guaranteed to not back out, at least if designed right)

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