[sitnievasnie]

Towing attitude

As we all know, the correct towing attitude is: -
The towed vehicle/s (when loaded) should be horizontal or slightly “nose down”.

Traveling back from Brits this Sunday, I noticed a number of vans being towed “nose up,” & having around 2H trip time to kill, I got a thinkin....

I just wonder, with the nose-up, and, under heavy breaking conditions, how big a role the tendency of the forward momentum of the towed vehicle to “lift” the rear wheels of the tug (and reduce breaking ability / tyre traction) would be, conversely when the towing attitude is set up correctly (slightly nose down) would the momentum then assist with tyre traction and by how much?

On a similar point,

Now me not be a engineer & therefore not tellibily phisisticated, I just towed alot & learnt what-not-to-do from other's ( & my) mistakes

For argument sake, a van, correctly loaded (80Kg -110 Kg on the nose & horizontal), would position the centre of gravity at a particular point within the caravan.

let us say that the C of G point was 300mm in front of the axle, along the centre line of the van and 800mm high from the centre of the wheel.

Shurly, lifting the nose from the horizontal would have the effect of “moving” the C of G backwards & upwards and if you lifted the front high enough you would reach a point where the van would tilt up on its own?

Thus a “nose up” attitude would then exacerbate the tendency to sway / fishtail? (Increasing as the nose is raised)?

PS Loved the article in the 50Th edition of COL

Back in MY day
We built em to float
We built em to break world speed records
& we built em so strong they was repairable after smashin…..

Regards
Warren
_________________
Go gently

[regstone]

Hi Warren,

This is my view of the situation, forgive if I repeat what you already know.
What you saying about the reaction of the towed vehicle drawbar force on the towing vehicle is correct if the caravan brakes were not working, but remember under braking the reaction on the towball is a downward force due to the turning moment caused by the position of the CofG of the van above the wheel axle. This will always be a downward force irrespective of the van being nose down or nose up with the difference being very small in comparison.

The height of the towball is normally around 450 mm from the ground when the caravan is level.
The height of the caravan wheel axle is around 300 mm, being the pivot point of the caravan. This gives an upward moment distance of 150 mm or there about depending on the van and tow vehicle combination.The down moment distance of the CofG will be far more, say around 1000 mm. This is a guess without doing a complicated calculation and will be different from van to van.

The stationary load on the tow ball of around 100 kg is now peanuts to what the load is during heavy braking, if the caravan brakes are working correctly. This additional load on the towball restricts the nose dive of the towing vehicle and thus improves braking on its rear wheels. The more the initial load on the ball the greater the load under braking obviously.

As we all know, it is always better to have the van and towing vehicle in line as was originally intended, it also looks a lot better.

Regards

Reg

[sitnievasnie]

Hi Reg.

Many Taaas, much learned by this cranky ol’ dog
Surprised that a “nose up” will also effectively apply a downward force on the ball,

I would’na worked that one out

The second part of my search for da truth
Does lifting the nose effectively shift the C of G backwards (& upwards)? Exacerbating sway

Many many thanks
warren
_________________
Go gently

[regstone]

Warren, Hi.

To answer your question, "Does lifting the nose effectively shift the C of G backwards (& upwards)? Exacerbating sway ".

Yes, but the affect is so slight it's not worth worrying about compared to correct mass distribution in the van.
Assuming the dimensions, C of G is 300 mm forward of the axle and at a height of 800 mm and the distance of the axle is 3600 mm from the tow ball.
Lets say the tow ball is 150 mm higher than the intended level condition.
Done graphically which is the easier and faster way, the C of G will move backwards 34 mm and upwards 12 mm by lifting the tow ball by this amount.
Unfortunately we cannot download the diagram to show the results but if 150 mm over 3600 mm creates an angle of 2,385 deg, then a distance of 854 mm (being the resultant distance) moves the C of G 36 mm at the same angle.

A slight correction to my previous reply. There will always be a downward force on the tow ball while braking, caravan brakes working or not due to the C of G being higher than the axle.

Regards

Reg