Nose weight conundrum
Can anyone explain please, why if for example I set my nose weight to 85kg with milenco gauge or bathroom scales, can I still lift the hitch up with both hands?
I mean that's like 3 bags of cement and I know for a fact that I can barely lift one bag.
I've asked several people who set this and all agree it's relatively easy to lift the hitch up but none of them would remotely be able to lift a fraction of 85kg.
I just can't get my head around this despite being in engineering all my life and am aware of leverage, moments, pivot points etc.
I'm thinking surely there must be a simple explanation.
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Comments
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Not much to do with caravans but interesting anyway.
Sadly, I have also pondered this and come up with the following thoughts.
Cement (or bird feed in my case) bags are awkward to handle and usually being picked up from the ground.
The tow hitch handle is comfortable to grip and starts at a height giving a straight arm, straight back lift so all the work is done with your legs which are surprisingly powerful.
Also 85kg is only about 13st so just a small person
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But you are not lifting 85Kg straight up are you? You are using a long lever and a pivot - the wheels. Your pull upwards is being multiplied by the distance to the wheels and give what is know as torque.
Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.
Archimedes
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I can't see any lever effect in play when you lift the nose of a caravan.
85kg resting on the nose weight scales would need 85kg straight lift to get it off of the scales.
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Yes there is.
No you wouldn't.
That 85 kg you talk about isn't the 'nose weight' but the moment of the force (lever and pivot) experienced at that nose. The scales are measuring the force, or torque, acting downwards on it and this calculated by the weight or force acting downwards of the hitch at that point multiplied by the distance to the wheels. To pull it up again you are using your own force multiplied by that same distance. You are not pulling 85Kg.
Just like Archimedes said two thousand years ago.
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Sorry, but I see as this, if the nose weight (downforce) is 85 kgs, then you have to counter act that with the same.
The nose weight is the imbalance of equilibrium over the pivot (wheels) in relation to the position of the end of the lever (hitch)
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Correct. The only reasons I can think of that may explain the OP's finding it easier to lift expected is that:
a. the OP has loaded or changed the loading of the van after the measurements were taken.
b. the measurements the OP took were wrong. Maybe the kit is faulty.
c. the OP has been overdoing the Weetabix or Spinach 😁. Maybe both 🙄.
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No, to your first. Again you counter the nose weight (torque) with a tuning torque of a similar or greater torque in the opposite (circular) direction. And the moment of a force is force times distance from the wheels.
You are not simply lift something upwards as you will be using a turning effect as well due to the fact that the caravan body can rotate about its wheels.
If you have a longer spanner then you can apply more force (torque, moment of a force) to a nut, true or false?
Think about this, if your A frame was 10 times as long as normal would it be easier or harder or the same to lift the hitch?
As the song goes, you cannae change the laws of physics.
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I respect the points that you make. We are measuring the down force weight at the hitch and not the turning force (torque) at the centre of the wheel.and we are assuming that there is no friction at the hub. Yes there is a link in that torque is the force x the distance ie, lbs/ft newton/metres.
By using a longer spanner doesn’t alter the turning force required at the nut but the force that is needs to be applied at the other end. If we were to extend the A frame whist still maintaining the same weight at the original hitch point, would the down force at the end of the new A frame position be the same?
John
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By using a longer spanner doesn’t alter the turning force required at the nut but the force that is needs to be applied at the other end
Sorry that does not make sense to me. There is no such thing as a turning force at the nut, only the effect of a force a distance away from the nut or pivot. Forces can only be applied in straight lines not around a curve (Ok apart from in charged particle physics I seem to recall). There is one force acting at the tangent that is important. This effect is called torque or the moment of that force about a point. As the distance alters the moment alters?
As the hitch will move in a circular arc when you pull it up, and is not a simple vertical lift of 85Kg and so it is subject to torque and all the physics behind taking moments. In very simple terms force you apply vertically will be 'helped' by the distance from the wheels and some of the caravan weight behind the CoG/wheels just like a seesaw.
It is as the OP states it is easier than expected to lift and certainly doesn't 'feel' like 85Kg
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Gareth, you are not lifting an 85kg weight, you are tilting an 85kg weight. I have owned cast iron woodwork machinery that weighs in at nearly 400kg and I've been able to raise one end to get a trolley underneath, but I'm dammed sure I could not lift 400kg. It is to do with levers, fulcrums, moments of force and pivot points.
Colin
Ps, you will only get a true reading from. Your nose weight gauge if the van is sitting on a level surface and the gauge is sitting on a flat solid surface.
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I think you are just underestimating your strength Gareth!
I agree you are lifting 85kg, but you are doing it with your legs (and back if lifting poorly), which is not a significant amount, have you tried to curl the caravan, I bet you cannot!
As someone else pointed out, this is only a medium side person, which I assume you could lift, even though you may not be able to wrestle 3 bags of cement.
Also remember that as you lift, the rotation about the fulcrum will change the centre of gravity, moving it backwards and act to lighten the load on the nose, though unless you are tipping it right up, this will only be minimal.
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Totally agree with your statement
Let's assume that the hitch is at exactly the height it was when the downward force was 85kg. The initial force required to raise the hitch by a mm will obviously be 85kgs. Admittedly the nose weight will reduce as the hitch is raised: eventually the noseweight will reach zero and then become negative.
Conversel,y the lower the hitch is to the ground the heavier the hitch will become - I'm sure many of us on here have had the misfortune for the jockey wheel to slip with the hitch ending up on the ground, It then becoming a 2 man job to raise the hitch to its normal height.
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