I’m sorry for the delay in replying, but there seems to have been some delay in getting all the posts from the old forum into the new one, and this thread seems to have become somewhat disjointed.
There are four basic problems with all the commercially available nose load gauges I have seen;
- Actual accuracy and consistency, (reports of variation of +/-30%)
- Clarity of the graduations (the ability to interpret the intermediate values)
- Changing length due to the applied load ( the natural effect of a spring under load)
- And the inability to adjust the length of the device to exactly match the load height of the cars tow ball
When the nose load is applied to the car, the tow bar drops because the suspension of the car has to adjust to match the nose load force. The bigger the nose load the further the suspension drops.
Exactly the same happens with the commercial nose load gauges. But there is a difference because of how far the gauge drops with the same load applied.
Unfortunately and most importantly, the nose load of every caravan varies depending on how high the hitch is.For a single axle caravan, if you were to drop the hitch to the ground, you need more force to lift it, than when the same hitch is at 400mm from the ground, and in some cases if the hitch is raised as far as it can be, the nose load actually changes to lift and the caravan will sit with its tail on the ground. This is all to do with the loci of the caravans CofG relative to the main wheels when the chassis is tipped.
The situation is even more complex for TA caravans, and the change between positive and negative nose loads can occur over a much smaller height range.
Consequently the height of the hitch is very very important in establishing what the actual nose load is applied to the tow car.
Most commercial load gauges have a much larger compression rate per Kg than the suspension of a typical car, thus you may be fortunate in finding that you caravan when it is loaded in a particular way settles at the same height on the car and the gauge, but make any changes that affect the nose load, and that happy coincidence will no longer apply, and the reading you get from your gauge will not represent the actual nose load applied to your car..
For those that claim to always load their caravan in the same way, consider that an empty gases bottle weighs less than a full one few bottles of wine on the return journey etc. Such factors may take you into an illegal loading situation.
The advantage of a pair of bathroom scales over a linear spring is that the actual movement of the weighing surface is in the order of a few mm for a weight range of 0 to 150Kg, thus the height error is minimised, compared to 100’s of mm.
It is also fairly easy to re calibrate bathroom scales using a water container with a measured amount of water to act as the test load.
What is needed is a stand with a load spreading foot to stand on a pair of domestic bathroom scales, and a standard 50mm ball at the other end that can be fitted into the hitch. The height of the stand is adjustable (preferably like a screw jack) so it can be fitted and easily and safely adjusted whilst in position to match the actual towing height.
I claim Copyright to this idea.
In response to John_37456491, your list of points
The compression of the jockey wheel is a very poor indication of the applied load, it relies on the surface it sits on, the degree of inflation, and the accuracy of your own judgment. Coupled to the fact that jockey wheels are notorious for loosing pressure, it is not a very safe method of judging nose load, and I seriously doubt that you could reliably detect even a 20Kg difference by that method.
The reaction of the A frame when using the motor mover, is again a very poor guide to the load imposed on it.
Together these methods may give an indication but you would be very unwise to rely on them as your defence if you were being prosecuted for over loading.
As for the actual sale of nose weight gauges,
In my view I have not seen one that is fit for purpose of adjusting to match the towed height, and to repeated and accurately measuring applied nose load of a trailer.
Your last point is not valid. The gauge its self is not dangerous. It will not inflict harm or injury to the user or to the public. It is the user who misinterprets the reading that is the potential danger.
You must also appreciate that there is a difference between illegal and dangerous. A product or condition that is dangerous is almost certainly illegal, but something can be illegal without necessarily being dangerous.
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