Why are wheel nuts tightened so much that they're almost impossible to get off?

[andymax]

My local well regarded tyre shop has signs up stating that any employee not correctly torquing wheel nuts when refitting wheels will face instant dismissal. Does your "well regarded" tyre shop do the same?

When I first started using them 30+ years ago, they were the best around, great service, great prices and yes they did torque the wheels when refitting.
Latterly, they still won't be beaten on price but that individual attention is missing as they are always busy. Some of the older fitters still there still appear to have some pride in their work and will torque. I should go somewhere else but there's a certain amount of inertia at my age means that I probably wont (unless there's a compelling recommendation for another tyre fitting service locally)..

 

[DucatiEVO]

Know that feeling, just picked up my car and took the wheels off, holy cow those bolts were tight!!! I was standing on my breaker bar to crack them off!!!

 

[Mercedes-2010]

I was always told not put any form of lubrication onto the wheel bolts or nuts, other than to wire brush the threads, apply a little WD40, allow to dry, refit and torque up. Reason, grease reduces friction between male and female threads thus allowing them to come undone.

If correctly torqued in the first place there should be no problem.

See below copied and pasted from www.greasemonkeydirect.com

"Putting oil or any kind of lubricant on the wheel bolts, wheel nuts, or wheel studs is a very bad idea. If the surfaces are encouraged to slip, as oil would do, the wheel can come loose. Rust on these areas is common, and it does not matter as it is only on the surface.26 Apr 2011"

 

[Mercedes-2010]

There are two reasons why this occurs:
---- Tyre fitters who are clueless
---- Tyre fitters who are paranoid about wheel bolts / nuts coming loose after they've fitted the wheel.
As said - Use a torque wrench - Not a ratttle gun.
Correctly-torqued wheel bolts will not come loose.
Good practice is to check the torque after 500 miles as the bolts bed in.

I've seen many of them on many occasions use a rattle gun to belt them on, if the torque wrench clicks or beeps they think it's the correct torque, in actual fact its way overtightened! The only is as already said on this post, tighten a little the torque to full setting and in the correct stud / nut order.

 

[190]

I was always told not put any form of lubrication onto the wheel bolts or nuts, other than to wire brush the threads, apply a little WD40, allow to dry, refit and torque up. Reason, grease reduces friction between male and female threads thus allowing them to come undone.

It's technically correct wheel bolts shouldn't be lubricated but I don't believe that's because they will come undone in fact quite the opposite.

Screw fasteners function by stretching below the elastic limit when torqued correctly and it's this stretching that provides the clamping force that prevents the fastener coming loose. The standard torque is specified for dry threads and the effect of lubrication with the same torque is to stretch the fastener even more resulting in higher clamping force, possibly even to elastic failure although that would very rarely happen with wheel bolts. Where anything is used that reduces the friction between threads then reduction in the torque setting is appropriate to achieve the required clamping force and prevent over stretching.

 

[BigJase88]

I lost a wheel once as my wheel had been that overtightened the studs snapped.

The wheel overtook me. Was certainly an experience

 

[DucatiEVO]

I lost a wheel once as my wheel had been that overtightened the studs snapped.

The wheel overtook me. Was certainly an experience

That happened to my brother too....but only because he forgot to tighten the wheel bolts!