sosij said:
I remembered the Prof saying something about a jockey wheel measurement being inaccurate due to it being set back from the hitch, so I tried it 'old school' with digital bathroom scales and wood - that gave 81kg
So the CWC seems very accurate - the discrepancy between the O/S & N/S wheel weights was consistent with the cooker & fridge being located on the N/S, so everything is fine, except getting an accurate nose weight via the CWC.
Does anyone know the formulae for calculating 'true' nose weights when measured at the jockey wheel? - I could, of course, simply deduct 24kg from the CWC indicated weight, but I'd like to sit down and work it out properly.
Ironically, now that I have established to true MIRO the CWC becomes superfluous - I will weight every single item of gear that goes into the van, and once those weights have been established it will be easy to determine what the van weights without the need for further weighing (which, of course, could have been achieved by simply taking it to the weighbridge in the first place! :lol: )
My main concern is the discrepancy between the weighbridge & CWC nose weights - at first I thought the lower bridge figure could be down to the 20kg margin of error - add the 20kg and it tallied with the CWC. However, the scales & stick method agreed with the bridge, so it must be the CWC that is weighing the nose weight wrongly.
However, the CWC axle readings seem spot on! - so what could it be about weighing at the jockey wheel that is adversely affecting the CWC?
I can only speculate about the variation between the readings from the Reich and the weighbridge, but I suspect you may just have demonstrated how variable the nose weight can be if its not measured correctly.
I must first remind you that with a single axle caravan, if you change the height of the hitch, the actual nose load changes. Its all to do with position of the caravan's centre of gravity and how it relative to the road wheels point of contact with the supporting surface. So if the caravan is on a slope or tipped to a different angle, you won't get accurate weight readings.
This is why I bang on about measuring nose weights correctly.
I don't know what type of weighbridge you used, and I don't know how you arranged to get the nose weight measured, but the one near me is not flush to the ground, it sits on top of a concrete pad and you have to drive up about 2m long 300mm high ramp to get to the weighing surface.
If yours was the same, the caravan would have its wheels on the ramp and the jockey wheel on the bridge. Unfortunately the caravan would be at an angle and that would reduce the applied jockey wheel load to the bridge giving a low reading. Coupled to that the inherent uncertainty of the measurement +/-20kG is a significant proportion of the likely jockey wheel load.
You must also bear in mind that the degree and the sign of the error of the weighbridge may not be consistent throughout it entire measurement range, so whilst it may come up as + 20kG at 2 tonnes it could be -20kG at 100kG load and still be within its required accuracy.
Now the same accuracy principle applies to the Reich CWC (and indeed all measurement devices). If I remember correctly Reich make a claim of a 3% margin of error, Now is that 3% of the reading or 3% of the full scale reading I've not seen it stated. - Most digital devices (especially Digital multimeters) will state their accuracy as so much percent of the full scale reading +/- 1 least significant digit So for the Reich with a full scale reading of 1000kG that could be a potential error of +/-31kG for any reading.
Let me say that no manufacturer can give an accurate MIRO. Each part that goes to make up the caravan will have some permitted tolerances which will also affect their weight. Each of these small variations will change the MIRO of any specific van, as well as things like Tyres, how worn, and how heavy. Different brands will have different weights. Equally you have to consider the weather! If the humidity is high then the wood in the caravan will absorb more moisture which will affect the weight of the caravan. Is it raining? So manufactures MIRO's are more of a guide than gospel. I know this might all seem a bit pedantic, but its quite possible for these variations can add up to a significant value.
There is nothing wrong with weighing every single item you put in your caravan, It will certainly make you acutely aware of how much items weigh and what you are taking, but do not be surprised if you find your calculated weight differs by several Kg from the caravans real weight.
This is because every time you weigh a small item, the resolution of the scales will create a small error which will all be added up and will appear on the bottom line. The sum of the errors may be exceed the error of your whole caravan weighing scheme. Incidentally the small errors could be under reads or over reads, they could also cancel each other out over the whole caravan.
Nose weight measurements can be calculated by using the jockey wheel post. This is not too complicated for single axle caravan, and once you have worked out the correction factor which will never change for your caravan, then using the jockey wheel as your nose weight measurement point has a lot going for it. You always have it with you, and it can be adjusted to give the correct hitch height safely and easily something that currently no retail product allows you to do.
The principle behind this is that the mechanical advantage of levers.
Effectively the nose weight of a trailer is trying to tip the trailer's hitch towards the centre of the earth, turning the caravan around its axle. This is applying torque to the main axle, and as you will know Torque is measured in Newton Meters (NM) The Newtons is the force applied and the meters is the distance from the fulcrum in this case the wheels axle stub.
So you need to measure the distance from the centre of the road wheel to the centre of the hitch and note it (Dh), then measure the distance from the jockey wheel post to the same point on the road wheel Dj). I specify the jockey wheel post to eliminate the variation caused by the actual jockey wheel not pointing in a consistent direction which will change the distance to the caravan's main axle.
You can use these measurements in two ways. If you have already decided on what nose weight you want to achieve, you can divide Hitch distance (Dh) by Jockey distance (Dj) (your result will be greater than 1.00) and then use it to multiply your desired nose weight
Desired nose weight x (Dh / Dj) = Maximum desired jockey wheel measurement.
To help you could write this on the block of wood mentioned below so its always handy
Or if you want to work out what your nose load is for any reading you get at the jockey wheel
jockey wheel reading x (Dj / Dh) = what is actually applied at the hitch.
Method:
You will need, a tape measure, a set of bathroom scales, and a block of wood to support the heel of the jockey wheel post so the wheel will not touch the scales when supported. Wheel chocks.
To take the weight measurement at the jockey wheel, The caravan and car must be loaded with luggage and passengers as if you are ready to start your journey.
Find flat surface (No slopes) big enough to position you outfit on, Stop and with all the passengers and luggage on board measure the height of the hitch from the road.
Put the wooden block on the scales and zero them.
Uncouple the caravan from the car, Chock the caravan wheels so it can't roll away and release the hand brake.
Support the heel of the jockey wheel post ona block of wood on a set of scales.
Adjust the jockey wheel height adjustment so you set the hitch at the measured height and take the weight reading.
Edit
I also note you intend to buy the Alko Premium Jockey wheel I accept your reasons for its strength, but its gauge - I wouldn't bother, its graduations are far too coarse, and others have reported they are not very accurate.
Just a note about the Reich nose weight gauge that Sprocket shows. It is a matter of physics that the nose weight of any trailer will change if raise or lower the hitch when measuring it For single axle caravan raising the hitch will reduce the nose weight by some margin. Exactly how much depends on the geometry of the chassis and how the caravan has been loaded. The exact amount is not a fixed value and it is not a fixed percentage for all caravans.
With that in mind as you can see, the Reich device sits on top of the cars tow ball and raises the caravan hitch by about 75mm. For this reason the device cannot give an ACCURATE nose weight reading. Reich apparently claim they have incorporated some correction, but it can only be an approximation as there is no user function to programme in the caravans details. Whilst it is not accurate, it is still far better than nothing, and used sensibly it will allow for legal towing.
The device is not compatible with twin axle caravans where the mechanics of the chassis and double suspension are far more complex.
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