Quote: Originally posted by brianconwy on 12/3/2012
Caravan wheels don't rotate any faster than washing machine drums on fast spin which are never going to be balanced. Washing machines rely on damping. Caravans have the weight of the van to help dampen vibrations, which maybe why swift found negligible extra vibration with unbalanced wheels.
The effect of unbalanced wheels on cars seems to become apparent at a certain speed. Maybe caravans never reach the speed where maximum effect occurs.
I am not arguing against balancing but if the manufacturers are not insisting on it then it might not be as important as it might appear. After all if there was any safety issue then there would be a legal requirement for it to be done on all vehicles.
Problem is long term safety aspects cannot be easily measured by a manufacturer. All manufactureres will have a cost vs risk analysis on their processes so they may well have decided on balance (excuse the pun) they won't bother with it.
Look at the tyres many manufacturers fit as standard, their load rating is barely covering the max permissable load and certainly doesn't fall into Tyre safe's recommended max load for example.
Anyone not having tyres balances at least when they chnage their tyres is penny pinching to the extreme IMO
I've just checked mine, & my dad's (been to the storage to get some Puriclean in the pipes).
They are all balanced, even the spare (we only have one between us ).
I have spent my life driving old bangers, I know full well what an unbalanced wheel feels like. Sometimes you can hardly feel it, if it's on the back. But when it's on the front you really know about it.
An unbalanced wheel/tyre combination will vibrate at all speeds, but it will indeed get worse, until it reaches it's point of resonance, then it will start to fade off again as you pass that point.
This isn't usually a set speed either, it all depends on the weights involved & the diameters etc.
It's also worth mentioning, as a tyre wears down, it may become out of balance. I've had it happen to me before, I once had to take a car in just to have the wheels balanced again. It was fine before, but I was doing a lot of miles. As the tyre wore it became worse. The fitter told me this can happen, he advised having them checked about half way through the life of the tyre.
I also know many Citroen 2CV's used to go without wheel balancing. This is because they only have 3 studs holding the wheel on, so are difficult to fit onto the balancing machine. (nothing to do with caravans, but I thought it was interesting nonetheless )
'Problem is long term safety aspects cannot be easily measured by a manufacturer.'
They can't be measured by manufacturers but they can be assessed by you. There is no safety aspect that has been caused by wheels out of balance on caravans. There has been problems with blow-outs which have nothing to do with balancing. I am not advising not to get wheels balanced, just that the people are exaggerating the consequences ( if any ) of following the manufacturers lead.
I don't accept that manufacturers balance the danger to peoples lives against saving a few pence on a £20,000 vehicle. When safety is an issue products are recalled at astronomic expense.
We can all have opinions but none of us has conducted the research that the manufacturers have.
Thanks all, many interesting points here - too man y to respond to all, however, a few points- the firm in question are used by local caravan stockists and are supposed to be specialist caravan tyre fitters, Ive never used before and this was why I was surprised by their response. Additionally, as I cant get work done at storage and my drive slopes I took the van to them. Total bill ended ub nearly £40 dearer than Tescos (use e-tyres I believe), plus a 25mile round trip.
If , as we all know, unbalanced car tyres can cause shake and steering wobble, the same will happen to caravan wheels, the fact that we are not aware of it would in my opinion be worse. Would have had tham take the tyres off if they had refused to balance them, which as I said caused them quite a bit of work, especially as they had to take one tyre off and rotate it to get it to apoint they could balance it.
Wasnt very happy about the originally offered 2 year old tyres either!!
I don't consider it a particular safety issue, But that is minor to the damage it constantly does to fitted equipment. So many instances I see near every single day, the gas fire and parts of the electric heating being particularly prone to vibration.
Iv'e just wrote a reply to a Truma Ultra-heat problem, limit stat mechanical fault caused purely by vibration inturn caused by out of balance wheels.
But there are dozens of other examples, some very expensive to repair down to screws inexplicably coming loose that are just annoying, but all avoidable by spending very a very few pounds.
As for the so called 'research', I believe 60 grams was as far as it went?, why not three times that?! 180grams and more are regularly reported on Bailey caravans!. What about all four at 60g out on a twin axle?
Even if I except 60grams is ok, and I DON'T because the proofs there, how do they know all are within their 60gram test limit? unless they test them all to find the bad ones.
And if they do that, why not stick the weights on while their at it? I mean 7/8 of the balancing is already done!!
Mine you, with the price of lead these days?!!!
Surely unbalanced wheels run hotter than balanced ones???
I would say that's a safety issue, wouldn't you???
Also, there are many very important components on caravans which "could" vibrate loose, like parts of the brakes & running gear, wheel nuts etc etc. I know the "shouldn't" come loose, but they can.
When a tyre is heavier in one place, the effect of centrifugal force is to throw that place further than the rest of the tyre.
The tyre has steel bands to keep it round so the bulge will need to pull these bands into an egg shape, the more weight the more egg shaped the tyre becomes.
Now the van is running on egg shaped wheels, the force the point hits the ground increase as the weight of the van tries to push it back into the round. To a great extent it will but some will force the van upward, this is happening 14 times a second at 60mph.
All this up and down movement is generating energy and that has to go somewhere in the form of heat and vibration, where it goes is anyone's guess, but you can be sure, it's causing harm somewhere.
So with all this damage to the equipment and the van, why would the manufacturers pay out on all the warranty claims rather than balance the wheels for very little extra cost. If people are worried about tyres going out of round then tyre savers are essential yet how many people use them?
'When a tyre is heavier in one place, the effect of centrifugal force is to throw that place further than the rest of the tyre.'
The weights go on the wheel so the tyre will still suffer these effects, but the stress on the bearings will be reduced.
My wheels on the caravan arnt balanced surely most of any out of balance force will be absorbed by the elastomer in the suspension which in effect isolates the wheels from the mass of the caravan in the same way engine mountings work if you watch an engine when it's running it vibrates and shakes ouite alot hence the need for rubber mountings The main problem for tyres and bearings is sitting under load for lengthy periods of time without moving alko recomend taking the weight off the suspension if the van isn't used for any length of time but most people seem to ignor this I agree that balancing the wheels will reduce some vibration but I don't think that it's the great panacea for all the problems associated with poor manufacturing standards
'If the weights going on the wheel make no different to the tyre going out of shape, then why or how does the assembly come into balanced?'
If you hold both arms out with a sock in one hand with a heavy rock in it, and the spin around, then the sock will stretch and there will be a force tending to pull you over. If you the hold a hammer in the other hand with the same weight and repeat, the force pulling you over will be counterbalanced but the sock will still stretch.
I agree with Phil in that there is no downside to balancing the wheels but I also go along with Swifts exhaustive testing that showed very little difference in vibration levels and far less than vibration caused by road surfaces.
Of course if you are going to get them balanced then it needs to be done regularly and tyres supported on tyre savers or the van moved regularly. Other factors like the addition of a locking bolt might alter the balance.
Quote: Originally posted by brianconwy on 12/3/2012
'Problem is long term safety aspects cannot be easily measured by a manufacturer.'
They can't be measured by manufacturers but they can be assessed by you. There is no safety aspect that has been caused by wheels out of balance on caravans. There has been problems with blow-outs which have nothing to do with balancing. I am not advising not to get wheels balanced, just that the people are exaggerating the consequences ( if any ) of following the manufacturers lead.
I don't accept that manufacturers balance the danger to peoples lives against saving a few pence on a £20,000 vehicle. When safety is an issue products are recalled at astronomic expense.
We can all have opinions but none of us has conducted the research that the manufacturers have.
As you correctly say we all are just discussing here - I do however have knowldge of large scale production and you would be surprised at what is done in nature of cost cutting. Saying manufacturers wouldn;t do it just based on cost is not correct i am afraid (much as we might like to believe otherwise)
Pennies and pounds are saved in areas that have large scale effect of profit margins on production lines and as I said above a risk reward analysis would be done to see if they can get away with not bothering to balance wheels as it saves money and apparently has no obvious detrimental effects on safety (although does apparently in many cases on handling of van)
As it costs so little why would anyone not do it would be my question. If it wasn't worth doing then you wouldn't do it on your car either would you?
Saying all that I do think correct inflation pressures and correct loading rating for tyres is far more of an important angle to get right first (load rating on caravan tyres is another example of cost cutting in previous years)
I used to work in the QA department of a firm making parts for Nissan, jaguar, Vauxhall and Land Rover. Modern quality systems have been refined which is why cars are so reliable. The cost of recalling cars and replacing components is prohibitive and also there is the PR disaster of any safety recall. Firms like Nissan would stipulate how the product was to be manufactured even down to requiring certain types of gloves to be worn for some tasks.Their attitude to good QA is that it saves money and so a few years down the line they expect the production process to be continuously improved and the supplied item to be cheaper.
QA in the caravan industry seems to be a different matter altogether but as you say the cost of balancing wheels at the factory would be negligible and I believe Swift in their assertion that their testing showed there to be little extra vibration and the cost of balancing was not a consideration as the testing done would have covered the cost of balancing the wheels of thousands of vans..
I think if you are going to balance your wheels then it is pointless if it is done and then not redone on a regular basis.
Brian, in the past when I worked as a QA manager Quality was about providing what the customer wanted as per your comment about Nissan. If as I suspect the customers of a manufacturer expect that wheels should be balanced then maybe it would be good QA practice to do so regardless of any engineering assessment that the manufacturer had made. If anyone can point me in the direction of the mythology that was used when Swift did the tests I would appreciate it as a lot of pseudo science gets touted with little scientific foundation.
------------- 'A sure cure for sea-sickness is to sit under a tree'
One of the foundations of QA is that anything should be made good enough to serve the purpose the customer needs it for.
As for your use of the term mythology then you will have to take that up with swift. They have the only forum I know of that is run by a caravan manufacturer where they address queries. There are many posts on the forum on this subject and anyone can look without joining the forum. e.g. see this one.
Forums are not full of science just opinions like yours and mine. As far as I know Swifts figures and detailed accounts of their testing aren't available.
I have always had my wheels balanced when having tyres fitted as I can't see any downsides, but having not done any testing on a circuit myself I wouldn't argue with other peoples testing.
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Topic: Wheel Balancing
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