Wheel Bolt Lubrication

[Paynewright]

I know that in general, unless otherwise stated, you shouldnt lubricate the threads on wheel bolts / nuts. As I understand it, altering the friction on the threads can lead to over torquing.

Anyway I’ve noticed when tightening the OEM wheel bolts to 180nm a sudden jolt (with associated noise) can occur nearing the correct torque and I’m unsure whether its achieved the correct setting or gone past it?

My Porsche has identical style bolts, same size with a conical shaped rotating bush albeit the bush is ally. In the handbook it states alu-slip should be applied between the bush and head of the wheel bolt.

So just swapped a wheel on the van after a puncture repair and using a snap blade I applied a tiny bit of alu-slip between the head of the bolt and conical bush. They torqued up smoothly without any sudden jolts. I’m guessing it was friction and a sudden release causing the original issue.

Thought I’d share for comment.

Ian

 

[Johnboy57]

I would say this is down to friction, or as is sometimes referred to as stiction. The two components become microscopically welded together, and as you apply the torque it suddenly releases. This situation is not good for controlled bolting - however don't think a wheel nut can be considered controlled in the true sense.

Metal to metal friction is subject to huge variations - add into that all the water ingress and muck off the roads and you really have very little control on the tension on the bolt if un-lubricated.
In laymans terms, you will lose 50% torque under the nut, 40% in the threads with only 10% actually tightening the bolt. These are approximate, but stiction could reduce the tension further.

Wheel nuts are well oversized and as such will give a very "stiff joint" which is what is really needed - you don't want any movement of the wheel which would then cause the nuts to rattle loose.

I often get the same issue when undoing nuts that have been tight for a long time.

I often put a small amount of grease on to reduce the chance of the stiction - effectively the same as the lubrication between your porsche insert

The conical insert on your porsche wheel nuts is there to prevent galling on the wheels as no rotational slippage occurs at the wheel.