Sevice wheelnut tightening

Posted on 15/01/2020 17:10 by JVB66

Tell tales as fitted to comercial vehicles negate the need (I am informed)to re torque wheel studs/nuts and milenco make tell tales for caravans as fitted to ours so a quick visual check is all that is needed as on other vehicles so fitted

Posted on 15/01/2020 17:55 by Lutz

Tell tales only show if a nut has rotated, but not if the bolt has stretched, and that would also negatively influence the clamping torque.

Posted on 15/01/2020 18:02 by JVB66

You mean if the stud had been over torqued? if that was the case it would start to unwind which the tell tale would show?,

 

Posted on 15/01/2020 19:25 by Lutz

Yes, I do mean that the stud was overtorqued, but the nut need not unwind for the necessary clamping force to be reduced.

Posted on 15/01/2020 19:43 by JVB66

I see no differences in how the telltales would not show a problem it seems to work on much more under stress wheels than a caravan that could well have "stretched"studs/bolts 

Posted on 15/01/2020 20:10 by

That is because you do not understand the reason for applying set torques to bolts. As Lutz explained a bolt can stretch and slack off without rotating. The idea of applying torque settings to bolts is to "stretch" the bolt and clamp the two surfaces together under tension

Posted on 15/01/2020 20:27 by ocsid

The tell tales as stated only tell you the bolt has turned.

Unfortunately here,  it is  however the tension in the bolt shank that clamps the wheel in place and loads the friction surfaces that stop the wheel moving against the hub.

The tell tales have not the slightest clue if the tension remains adequate to stop the wheel from starting to move and fret, as the bolt only starts to turn long after the required tension has been lost.

Wheel bolt tension is most typically lost because some thing or things have started to settle under the alternating forces. Of these dirt, plating, paint, surface corrosion or traces of grease are what typically "settles".

Unfortunately, by design our common caravan bolts have a short elastic length, the bit of the bolt elastically strained, so any settlement quickly reduces that all important bolt tension on which the wheel retention relies. Better designs feature a longer strained length to the bolt to reduce the magnitude of tension loss from similar settlements.

Or, as in challenging applications a collar is introduced simply to increase the length of the bolt subjected to the strain. In our case this is offered as WSL safety bolts, the collar increasing this vital stained length by 3.5 times the normal.

There are arguments for tell tales on large number of bolt applications, greater than our 5, but basically these are to highlight where sloppy workshop or roadside practices can have left the odd bolt way under tensioned. With just 5 bolts on our heavily loaded wheels every one has to "pull its weight" or wheel loss is imminent, typically way before a tell tale would give any hint. They of course are in our caravans case a nice little earner for the retailers and makers.