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Over recent years we have had a large number of caravan insurance claims where a wheel has become detached and caused an accident. Such accidents often result in costly repairs and more significantly can be extremely dangerous to you and other road users. This article aims to highlight the importance of setting a caravan’s wheel nuts to the correct tension, and checking them regularly, in order to reduce the risk of an accident when towing your caravan.
It’s important that you check your wheel nuts for tightness regularly: we would advise you do this before every journey.
Caravan wheel nuts have a specific torque that they should be tightened to, which may differ from one manufacturer to the next. This figure should be in your caravan’s handbook.
Invest in a good torque wrench
In order to set you’re caravan’s wheel nuts to the correct tightness you need to use a torque wrench. Torque wrenches can be set to a specific torque and won’t let you tighten a wheel nut past a certain point no matter how much force you exert.
A good quality torque wrench can be picked up relatively cheaply, with the mechanical non-digital torque wrenches being more than adequate for use on caravan wheel nuts. Torque wrenches with a digital mechanism are generally more expensive and aren’t really necessary for the level of accuracy needed for a caravan. Most non-digital torque wrenches will either; bend at a hinge, make a loud clicking noise or have a pointer and gauge to let you know when the correct pressure has been applied.
Checking tightness down the line
There is some debate about the correct way to check the torque of your caravan wheel nuts once they have been tightened up and left alone for a while. Some manufacturers recommend a ‘re-torquing’ technique whereby wheel nuts are loosened slightly before being retightened to the correct level. This is due to something latent friction, which basically means you can’t get an accurate torque reading from a bolt which has already been tightened because the little bit of extra friction caused by it not moving will give an inaccurate reading. This is also why it is important you tighten up your bolts in a fluid motion in order to get an accurate torque reading.
That said, you can use a torque-wrench to see if a bolt has come loose because only a very slight drop in the torque tension of a bolt (say 5-10%) would be overcome by the latent friction. So whilst it’s true you can’t get a 100% accurate reading from simply checking the torque of a nut with a torque wrench set to the same setting it was when you first tightened the wheel, you can get a rough guide to if they have moved significantly.
Use the right products for the job
Also be careful about what products you use on your caravan wheel nuts. If your wheel nuts become stuck then don’t be tempted to spray WD40 or another lubricant anywhere near them, as whilst it might help in the short term it could have serious long term effects on the ability of the nuts to hold tension. Your only safe option is to simply be patient and use a wrench with good leverage to work the bolt loose.
If you have the opposite problem and want to help your bolts to stay securely in place for longer then you need to use a substance such as Loctite (speak to your local dealer or visit the Loctite website for advice on which variety is best to use) which will help to give the bolt’s thread extra grip but won’t permanently stick the bolt in place.
And when someone gets injured who is going to be held negligent in the legal case? I had a colleague who lost a caravan wheel when it came off and rolled down a valley in France – that was 30 years ago and steel wheels were fitted to caravans in those days, so it’s always happened.
I e mailed eldiss last night for the wheel torque settings for my van. Got a reply this morning with all the info i need. Service or what ?
That’s brilliant Paul – the kind of service you expect from manufacturers.
I don’t think it is necessary to check bolts as often as suggested but before each significant trip is advisable. It is easily possible to overtighten a bolt/nut with a torque wrench. You must only tighten it until the wrench clicks if you are using that type. Do not give it that extra tweek which I’ve seen badly trained fitters do. Apart from anything else you may find you can’t get the wheel off at the side of the road. Twin axle vans need extra attention as the wheels fight each other during cornering and manoeuvering which tends to put more distortion into the wheel and the bolts and as previously stated it is this wriggling of the components which causes minute wear between the mating surfaces and eventual loosening as the strain energy is lost. Look after your vehicle and it will look after you.
Never a truer word said Jock! Thanks!
One possible solution is to fit tags on the studs , as they do on comercial vehlcles.Then you would be able to keep check to see if they were coming loose.
I am also an engineer with over 40 years experience in the manufacture of componenents with threads and tapers ect,on reading the various comments it strated to make me think about dimensional tolerances of these components and are they within drawing limits. It is important that screw threads conform to the correct tolerance on size, thread form, and surface finish on both the hub ( female thread ) and the retaining bolt ( male thread ). Loose fitting threads tend to slacken off when subjected to rotation and vibration especially on the poor state of repair of our roads today. the locking of the the wheel to the hub securely depends on several factors.
1) Is the tapered cone on the bolt and hub conforming to the limits and fit tolerance, as it is the tapers fitting together that locks both together securely ( good fitting taper is difficult to separate )
2) Is the pitch circle diameter of the holes on hub and wheel identical with no mis-alignment.
3) Always tighten to the recomended torque setting for your van and sequence usually 1,3,5,2,4 and as stated tighten until the wrench clicks once. Do not go past the click as you will be able to futher tighten the bolt as stated by Jeff.
4) I agree with Jeff about the excess clearance between hub and wheel this should be a close fit enabling the wheel to be located on the hub. If this was done then this would dramatically reduce the load on the retaining bolts and let them do the job they are ment to do, lock the wheel to the hub.
Thanks for your comment Tom, some really helpful advice there!
Among the dangers are that the bolt may not actually be tight enough, depending on the length of the brace or bar etc. with obvious consequences.
Then again, the bolt might be too tight which can cause catastrophic failure. The bolt seat (hole) in the wheel could be stressed and crack (especially alloy wheels, but steel can be affected too). The bolt might even strip some metal from its threads so it won’t mate properly in the hub resulting in insufficient surface contact within the threads; it could pull out. Or the part of bolt may stretch and develop a waist. This waist means that the bolt has undergone plastic deformation rather than the elastic deformation that we need to keep the bolt under tension.
And of course (especially with alloy wheels) it can cause the wheel to stick firmly so that even with all the bolts out it will not come off the hub.
The lucky people who overtighten the bolts don’t have an accident, they just end up with a bolt that is really difficult to get out.
Considering the cost of a torque wrench, it’s just not worth guessing.
With only two major chassis manufactures ie Alko and BPW is it not their responsibility to ensure that the running gear is suitable for purpose Maybe a class action is now required.
I am also new to caravanning and am now worried about my nuts too! When I purchased the van, I replaced one of the existing nuts with a locking wheel nut (from Milenco) and nipped in to Halfords to buy a torque wrench. The helpful chappie said a torque wrench was overkill and all I had to do was get the nut to nip up and the “give it an extra tweak” and it would be fine!!
Possibly a daft question but is it possible to overtighten a nut? I don’t mean to the point of shearing it off but if you just get it as tight as you can by hand? I have changed many car tyres in my 30 years of driving and have never used a torque wrench on them? Althought reading above, caravans do seem to be different!!
I am also new to caravaning and we have just replaced our tyres which had run flat bands on which were very awkward to fit back on. After reading these comments I will be getting a torque wrench but I would also like to say I am a Bus Driver and the wheels on buses are torqued at regular intervals as they have a tendency to come off if not checked regularly, sometimes when I start in the morning I have to wait for them to be torqued before I go out!
Kind Regards
Paul
This has really put the wind up me as I’m new to caravanning, but no mention was made of checking wheelnuts by vendor company.My next purchase will be a torque wrench ! Any other relevant,( hopefully less frightening) pointers.
Joslin Barry
I’m sorry we’ve put the wind up you. Better safe than sorry I suppose. It’s certainly worth carrying out this simple precaution before every trip. Apart from that you could check out our other advice articles here.
Kind regards
Craig
Caravan Guard
This is sound advice and I would agree that the practice of checking wheel nut tension should be adopted, but I would also extend this practice to your towing vehicle. It has been known for motor vehicle to leave the wheel drums.
Mr J. Ross, Great suggestion to check the tow car wheels too!
Craig
Caravan Guard
just to add my bit – I mailed in some time ago after I lost a wheel off my swift 580 in the middle of France. Have now changed van for a new Coachman – collected and brought home : about 80 miles.
After my previous experience I am very wary of wheel security.
Checked the torque – and found to be at about 65 lb./ft. – supposed to be 95 !
also had wheels balanced one was 50 gram out and the other about 20
This just reinforces the necessity for regular checking – until the manufacturers stir themselves and get a proper engineering solution to the problem.
So if fitting new wheel bolts fixes an inherent design fault that might cause wheel detachment, then it could be argued that caravans without this new type of wheel bolt are not fit for purpose. Maybe all those caravans currently on the road would need a retrofit at the retailing dealers expense (sale of goods act).
OK – so I check my torques before every trip. But your suggestion that we should do this every 50 – 100 miles to overcome a design flaw in caravans is outrageous. Insurers see the consequences of the problem with wheels; they need to bring pressure on manufacturers to fix the problem. Passing the buck onto customers who trust manufacturers to supply safe products is not acceptable, and unreasonable. If it was wheels coming off baby buggies, there would be uproar.
Hi Delwyn
I think you are right. That suggestion does seem unrealistic in hindsight so I will amend the blog post to only advise checking before every trip. There is now a company producing a caravan specific wheel bolt that promises to remain tight over long periods of time. This is available as an aftermarket product but is also being adopted by a leading caravan manufacturer as a standard fit. We’ll report on this very soon.
Kind regards
Craig
Caravan Guard
I agree with the theory of differential expansion, but there is one other difference between the way caravan wheels fit and the way tha car wheels fit.
Let me expalin: when you mount a wheel on a car the centre hole in the wheel is a good fit on the hub, and all you do after lifting it on is to rotate the wheel to align the bolt holes.
But when you mount a caravan wheel, the hub is far smaller than the hole in the wheel. Not only does this make it a bit more difficult to get the bolts into alignment, but also the whole weight of the vehicle is held on the bolts, so any slight reduction in clamping allows microscopic movements of the wheel in relation to the hub. It is this movement that then continues to slacken the bolts.
One error in the article above it states “Torque wrenches can be set to a specific torque and won’t let you tighten a wheel nut past a certain point no matter how much force you exert.” But this is misleading. I know that it states later on about the “click” but this sentence should be deleted.
I really can’t believe that this problem of wheels falling off caravans has been going on so long, yet all the advice we get is torque the wheel nuts every 50-100 miles, which is totally impractical, yet they seem to have done nothing to solve the problem. As your previous contributor stated, we don’t hear of many wheels falling off cars. I travel to Spain every winter towing my caravan. I check the wheels every morning before setting off, which to my mind is too often, and have not had a problem. No one has ever suggested I check the lug nuts on my tow vehicle. What is going on?
Bit of a coincidence – i have just suffered from loosing a wheel off my Swift Challenger 580 whilst driving down through France – not a pleasant experience ! – I was very lucky as i was coming up to a pay booth so was only doing 30 mph.
I am an engineer with over 40 years experience – and am old enough to actually read the instruction manual – which i followed to the letter – not that it seems to have done me any good !
My thoughts on this issue are : the wheels are cast alluminium whereas the 5 x retaing bolts are h.t. steel – the expansion rates of these two metals are dramatically different – so when the wheel expands it becomes trapped / crushed by the bolt head . When there is a cooling period the wheel contracts and a gap is formed – therefore the bolts are no longer under load.
I understand this problem is predominantly with the nearside wheel – this is because the direction of rotation applies a ” undo ” force – whereas the off side tends to naturally ” tighten ” the bolts.
An obvious engineering remedy is to use left hand threaded bolts on the nearside – but i am not convinced this is a total fix as the expansion rates problem is not addressed.
I do wonder what/ if there is a difference in manufacture process between van wheels and cars – as you don`t hear of cars loosing their wheels.
There is obviously a serious safety issue – but i have yet to hear of any response from the industry – I don`t think they can afford to ignore it .