Easier method for measuring nose weight??

[TrevorM]

I was going to add this to one of the existing nose weight related threads, but having produced it there did not seem to be a totally appropriate one. Since it has taken me some time, rather than waste it completely, I therefore decided to put it on a new thread. Anyway, here goes; please bear with me!

Because I consider the nose weight to be the most important (but not the only) factor influencing stability, I try to make sure mine is around the right value. I have both a Towsure gauge and a Reich Caravan Weight Control gauge.

One technique I have used, which I admit is not 100% accurate (but then what is,) is to weigh underneath the jockey wheel rather than at the coupling head. This has the advantage of not having to ensure the Towsure type of gauge is vertical, and the right height when measuring.

All that is needed is to check the weight on the jockey wheel with it in line with the caravan, facing forwards, at the correct level and standing on level ground. It is now easy to obtain the correct height by adjusting the jockey wheel up/down. Now, I hear you all say "but this will give an erroneously high reading!" This is true, but I believe an approximate correction can be applied as follows:

Multiply the measured weight by the distance from the caravan 'axle' to the jockey wheel axle, then divide by the distance from the caravan axle to the coupling head socket centre.

Diagrammatically:

! AC

Coupling !

!

! AJ !

! Axle position

O

Jockey wheel

Coupling weight = Jockey weight * AJ/AC

On my 'van I usually set the jockey wheel weight to be 80Kg, which I believe keeps me just the right side of my 75Kg hitch limit.

If you do not like the idea of crawling around with a tape measure, the multiplication factor can be established by measuring the nose weight by the traditional method, then checking the weight at the jockey wheel under the same conditions. The multiplication factor equals hitch weight divided by jockey wheel weight.

Sorry about the length - I hope it makes some sort of sense!

It is very straightforward in practise, and I would be interested in others' opinions. Please note though, I did say it is not 100% accurate.

Enjoy your holidays

Trevor M.

 

[TrevorM]

Sorry, the diagram did not work properly. AC = c'van axle to coupling distance, and AJ = c'van axle to jockey wheel axle distance.

Enjoy your holidays,

Trevor M

 

[ProfJohnL]

Hello Trevor,

You have correctly identified the fundamental leverage problem with weighing the nose weight at the jockey wheel position.

It is also correct to say that the load at the jockey wheel will be slightly higher than the load at the hitch, but only when the measurements you identify (axle to jockey and axle to hitch and height of hitch) are taken into account will the difference be revealed. It is of course potentially different for each caravan model depending on the distances between the axle and hitch and jockey wheel.

In the interests of accuracy, you will appreciate that if the jockey wheel is used to apply the load to the scales, the direction of the wheel will also affect the reading. If the wheel is pointing backwards, ten the the load will appear to be greater that when it points forwards because of the different distances between the axle and the point of contact with the scales.

Care must be exercised when assessing nose loads, as a load that is greater than the permitted allowance will technically render the outfit illegal, and the insurance void.

 

[Nidge1]

Trevor,

I thought your heading said " A easier method for measuring your nose-weight" Crikey, I'm just off to book my open university place!.

Nidge

 

[grandadbaza]

Not quite sure if this is a wind up posted by an eccentric mathmetician or deadly serious, anyway whichever one you are which axle do I measure to on a twin axle van???

 

[Lutz]

Theoretically, if the load distribution between the front and rear pair of wheels of a twin axle is even, as would ideally be the case, one could use the midpoint between the two axles as the datum. However, it is doubtful whether this is always the case as it depends on the height of the towball when the caravan is hitched up (the lower the towball, the higher the load on the front pair of wheels, and vice versa). This complicates matters further if you want a really accurate figure.

However, whether any normal gauge is that accurate anyway is also doubtful, so what's the point of working out the noseweight down to the last decimal place? If you're that close to the limit that you have to know the noseweight accurately to the nearest kilo, you're cutting it a bit fine anyway.

 

[TrevorM]

Thanks for looking and commenting on this folks. It is really not as complicated as it seems!

I just think it is much easier to check the weight under the jockey wheel rather than under the coupling head for a number of reasons.

For twin axles, Lutz's explanation is, as always, well considered.

My own view on twin axles is that if the nose weight appears to be at the commonly agreed 'lower of car's and van's recommended maximum values,' on level ground, then as soon as the towing vehicle begins to raise the hitch when in motion, this results in the weight exceeding the permitted value. I have not done the calculations to estimate the extent of this increase (since my van is a single axle,) but I imagine it could be considerable. I realise at higher speeds the effect of wind will also be a significant factor.

Enjoy your holidays,

Trevor M

 

[eckiew]

I was a forklift driving instructor and operator examiner for a good number of years and the same principle applies to caravans as to forklift trucks i.e.counterbalance, which is the seesaw effect. The centre of the axle is the pivit point for the 'seesaw'. The centre of gravity at any given time dictates the nose weight of the caravan and and if the centre of gravity is directly above the centre of the axle the caravan could be balanced with no effort, but due to the regulations and desire to have a noseweight the centre of gravity on a STATIONARY caravan is always in front of the axle.

A good way to understand the centre of gravity is to put a couple of bags of sugar (or a few cans!) in a box and hold it close to your chest and you will have to lean back to compensate for the weight which wants to tip you forward and move your body from the perpendicular which would be your centre of gravity, extend your arms and the weight will seem much heavier, what you have done is moved the centre of gravity further forward from holding it to your chest. The human brain will correct posture to allow the carrying of anything in front of the body (noseweight)but a caravan has to done by calcuations.

When a caravan is moving the centre of gravity is constantly moving and the noseweight is constantly changing too.

You will also notice if your hitch is down on the ground it is much harder to lift than if the van is nearly level as the CofG is further forward with the'van having a nose down attitude.

Therefore Lutz and others are correct in stating that the only correct way to measure noseweight is to load the van with all you take,level ground and very important the height of the hitch from the ground when hitched to car (also laden).

Hope this helps

Alex

 

[ProfJohnL]

Hello again Trevor,

Alexander has given a good account of what happens, so in fact it is the opposite of what you described in your last posting.

What as not been mentioned in this thread is that hitch must be between 350 and 420mm (measured vertically from the ground to the centre of the ball) when fully loaded and hitched to the car.

Because of these limits, and the fact that the lower the nose the greater the nose load, if a gauge were arranged to set the hitch at 350mm and the maximum nose load is created, then for all other heights within the 350 to 420 mm range the nose load will always be slightly less than the max and within limits.

 

[eckiew]

Hi John L

I was assuming that (rightly or wrongly) that people would know the reg.hight for their towball. Another thing to consider that many towers consider that the heavier the noseweight the safer it is to tow. this is not necessary the case as a caravan has in theory three points of contact with the road, the two wheels and the hitch which is supported by tne vehicle. In effect the same as a tricycle and we know when the front wheel of a trike is turned sharply - turnover time.That is why so many vans flip over when jacknifing. The car has some stabilising effect but not to the extent to prevent the van turning over.

A twin axle van should have the CofG ahead of the rear axle. According to Alko the maximum 100kg noseweight is to reduce wear on the hitch drawbar.

Incidentally Alko supply a guide for calculating noseweight if you buy one of their jockywheels with the loadgauge built in.

Alex

 

[TrevorM]

Alexander and John L,

I agree with what you say about the centre of gravity effect. My comments on a twin axle were based on the 'effective' fulcrum moving forwards and backwards when the hitch is lowered and raised respectively, ignoring c.o.g. changes.

My assumption was (rightly or wrongly) that the change in position of the fulcrum would have a greater effect than the movement of the c.o.g.. I based this on the fact that if all the weight were taken on the rear axle the nose weight would be higher than when the weight was on the front one.

If raising the hitch from the working level on a twin axle reduces the nose weight, then my assumption was wrong, and the c.o.g. has more effect than I had imagined.

It would be interesting to hear if anyone has experimented with heights and weights in this way.

Thanks to all for taking the time to respond; I note that no one has actually said whether they think it might be easier to measure under the jockey wheel than the coupling head.

Enjoy your holidays.

Trevor M

 

[ProfJohnL]

Hello again Trevor,

I agree it would be easier to to use the jockywheel as it is always present, and conveniently reaches the floor and allows you to adjust the height. But for the reasons above, it does not give a definitive reading.

Over and above the normal safety considerations, when using the jockeywheel many of the same precautions need to be observed to enable an accurate assessment of the nose load to be ascertained as when taking a true nose load measurement.

The measuring must be done on level ground,

The hitch must be at the same height as when it is connected to the car,

The jockeywheel castor should be pointing same way relative to the caravan chassis - or always use the stem of the jockeywheel

The correction factor to convert the reading at the jockey wheel to the nose load should be worked out and applied.

I suggest using the bottom of the jockeywheel stem, rather than the wheel its self, as it has a fixed geometry with the the axle, where as the wheel can change direction and thus the distances between it and the axle will alter. It should be possible to create a conical 'foot' which locates in the bottom of the jockeywheel stem and then spread out to avoid point loads on bathroom scales.

The correction factor needs to be calculated for each type of chassis arrangement. Fortunately it will be a simple multiplication factor, as the relative ratio of the lengths between the main axle and the hitch or jockeywheel will remain constant.

An enterprising manufacture could design a bespoke cone with a gauge built in. And the correction factors could be produced in a table form, or even a direct reading circular slide rule, easily kept in the caravan along with the gauge. I am aware that Alko offer a jockeywheel with a built in gauge, but the example I saw was not very well graduated.

 

[Robtel]

I think I agree with Nidge on this, a degree in mathematics required here!!!

Seriously though there does seem to be varying thoughts on how to accurately determine noseweight, everytime this topic appears I have never came across a method that everyone agrees is accurate.

As some one has pointed out towing with a vehicle in excess of maximum permissable noseweight is illegal but how would the responsible authorities guauge the noseweight? Does anyone know what mechanism or technology they use.

I use the typical "telescopic" tube type of guauge but according to my reading of the various threads it might not be accurate as it can't be set for the height of the towball.

Robert

 

[eckiew]

Hi Robert

One way to check your noseweight with the hitch at the correct height would be to measure the height of your hitch on the telescopic gauge and as you should already know the height when connected to the car note the difference in measurements and then pull the caravan up onto boards in thickness corresponding to the measurement difference. A bit fiddly but as near as you will get without that maths professor.

Alex

 

[Paul_5064559]

No-one seems to have commented on Trevors statement "On my van I usually set weight to 80k to keep right side of my 75kg hitch limit"

Surely this putting the cart (Van) before the horse (Tug)!

Hitch weights should be governed by the van not the car.

For example does not the van hitch weight need be something in the order of 7% of the vans gross laden weight and if this exceeds the tow vehicle manufacturers recommended towball weight, you need a tow vehicle change.....

Also it might be argued that if a vehicle manufacturers hitch weight is 75kg that is what it should be and not even 5kgs more.

 

[Lutz]

The noseweight limit for the caravan is typically 100kg, but the limit for the car is often only 75kg. Obviously, in such cases, one can only set the noseweight to 75kg or else the limit for the car would be exceeded.

The 7% formula can safely be ignored. It originated in the days when caravans were lighter and there were no manufacturers' limits to be observed. At the time, the 7% figure served as a guideline because no better information was available. Except perhaps in exceptional cases where the car's limit is well below 75kg but the weight of the caravan is over about 1300kg would a change of towcar be advisable. However, I cannot think of an actual example of a car with a maximum permissible towload exceeding 1300kg which would fall into such a category.

 

[ProfJohnL]

Hello Paul,

In my first reply to Trevors lead, I referred to his nose weight assumptions. And though I did not openly express it, I did question the accuracy of his figures.

With regard to the 7% and the permitted loads Lutz has already furnished you with a reply.

 

[TrevorM]

Hi, it's me again. Paul, the reason I aim for 75Kg at the tow hitch is that this is the limit for my towing vehicle. Lutz (as always) has explained the reasoning behind this excellently.

John L, I did say in my original post that the method was not 100% accurate. I also agree the jockey wheel position is crucial to obtaining an 'accurate' reading.

I do find it easy, with the caravan attached to the car, to place my Reich Caravan Weight Control device (CWC) (+/- 3% according to Reich) under the jockey wheel; I then lower the jockey wheel to the CWC and unhitch while counting the number of turns taken on the jockey wheel handle to clear the tow ball. Once the car has been moved forward a few feet, I then raise the jockey wheel by the same number of turns, hence returning the coupling to the original hitched height. I then move and reset the CWC, before replacing it beneath the jockey wheel and taking the measurement. Of course bathroom scales could be used instead.

I do have a telescopic nose weight gauge, but because it compresses by quite a distance it is not easy to achieve the correct height.

Thanks again for everyone's input.

Enjoy your holidays,

Trevor M.

 

[xtrailman]

While the 7% is only a guide, it has served me well.

I certainly, would rather ignore the advice of individuals, who rubbish the sound advise, given by the Caravan club.

The CC has to be very carefull about anything it publishes, due to the possiblity off liable action.

 

[Lutz]

Do you mean libel action or liability? Libel action can't apply because nobody's reputation is being damaged. Liability can't apply either because it is quite clear that one cannot exceed the respective car and caravan manufacturer's limits. As most caravans have a 100kg noseweight limit, 7% would not be achievable with a caravan of over 1430kg even if the towcar's limit were higher. In general, high noseweight makes an outfit more stable, so why not make full use of what you are allowed, even if the caravan is lighter, and forget about the 7% formula? I doubt whether the 7% was ever determined through very exaustive research - it was probably based purely on judgment.

 

[ProfJohnL]

Hello Ray,

If following the CC's guidelines works for you then that is fine, but it does not work for every one.

It is very strange that you dogmatically choose to ignore the technically derived results from the vehicle manufactures in favour of advice derived by a committee who do not publish the evidence or the methodology they used to come up with a neat figure. This applies to both the 85% towing ratio and the 7% nose weight recommendation.

I do not challenge the principal of keeping the trailer mass as low as possible, or the nose weight as high as is possible, these are sensible aims but as I have stated numerous times before the vehemence that some use to brow beat everyone to conform to arbitrary figures that have no evidence based validity seems incredible.

The approach of using the CC's figures in isolation of proven evidence is illogical, and being so it gives false sense of security to those who believe that by simply conforming to these figures will give them a a stable outfit. It is no guarantee.

The issue of weight ratio and nose load should be used as part of a package of measures, that must include loading practice, and driving style and not followed in religious isolation.