Prof ,There are several factors at play here some may allow the fastener to relax a little as the compressed materials settle, and other mean once the fixing has torqued, to move it any more requires several percent more torque to over come the static limiting friction to actually get the fastener rotating
In the context of wheel fasteners these differences are insignificant and we can in practice ignore them. and checking the torque settings should make no practical difference to the safety or effectiveness of the fasteners.
For 40 + years all my caravan wheels are rebalance after a tyre change.Mandatory in my book !Generally because wheels can have a habit of falling off caravans but not off of cars or aircraft 🤔
Manufactures don’t balance wheels so there is another added factor…shaking the van to bits.
I don’t think that caravans go through the same processes as aircraft where everything is signed off a hundred times before it can move either 🤔
Add to your list what I posted in #9 regarding undersized bolts in the UK. Why are UK bolts smaller than Continental on Alko chassis?Firstly Dusty, It may not have come across clearly from my last post, but I'm not advocating no secondary checking, only that if you do check the torque its not going cause the applied torque to rise unduly if at all.
As to the need to check the wheel torque after some distance or before every journey, as it does no harm. As Roger has intimated, there is a history pointing to an unreasonable number of caravan wheels coming loose.
This either means the fasteners worked loose, or the metal flanges being clamped was prevented from making full metal to metal contact by contamination, which when subject to teh dynamic forces of being towed and the mass of the caravan caused the contamination to be ejected or worn away reducing the clamping force and allowing the fasteners to work loose.
There is still no confirmed reason for why the fastenings work loose, but undoubtedly its belt and braces to make torque checks a pre flight check and if nothing else it can bring peace of mind.
Are the bolts smaller - or is the hexagon head smaller? UK caravans seem to use M12 (12mm) bolts with a 19mm hexagonal head - it's possible to get M12 bolts with a 17mm hexagonal head.Add to your list what I posted in #9 regarding undersized bolts in the UK. Why are UK bolts smaller than Continental on Alko chassis?
I have been told that smaller bolt diameters give manufacturers more freedom to choose aesthetically prettier wheels.
Perhaps that is true.
That Caravan Club report does end with the comment "The NCC, through its TechnicalAs I said earlier this issue came to a head 12 years ago but seemed limited to Bailey Unicorns.
This link explains exactly what happened and the solution. Why Roger’s chaps have raised it again , now is a mystery. Has something else happened that we don’t know about?
I will still check the bolts as before , clearly it does no harm and as the apron said it will not cause the torque to rise if at all.
I don’t know the head hex size, but the bolts are M14 on continental vans, the extra frictional grip has to be verysignificant.Are the bolts smaller - or is the hexagon head smaller? UK caravans seem to use M12 (12mm) bolts with a 19mm hexagonal head - it's possible to get M12 bolts with a 17mm hexagonal head.
As an update to my OP, it seems that some workshops have been fitting these low-friction replacement bolts for years, over 10 years in one case, but without any publicity and insisting that replacement is done by trained technician, not DIY. I want to know why the industry is so secretive on this issue.