Caravan Weights & Masses Analyser

Amigo1 · Member

Caravan Weights & Masses Analyser

Whenarewethere · Guru

I did a spreadsheet for everything we put in the car. Frightening how the little things add up. 24kg of things under 1kg not including clothes or food.

Or simply upgrading the tyres, another 6 (2 spares) X 3kg, 18kg we have to reduce elsewhere.

Peter_n_Margaret · Guru

One of the most important aspects of van loading that you can not measure on the weighbridge is the yaw inertia.
Yaw inertia is the effort required to start the van turning (spinning) left or right and the energy to stop it from turning once it starts.
High yaw inertia happens when weight is concentrated at the ends of the van rather than over the axles. A van can have high yaw inertia even if the ball weight balance is perfect and the van is not overloaded.
Yawing uncontrollably is what causes vans to snake down the road and then roll over.
Long heavy vans are at greater risk compared to shorter lighter vans.
Bath University in the UK has done some studies on yaw inertia with caravans.
Cheers,
Peter

Bagmaker · Senior Member

and Roll inertia.
Heavy up high combined with heavy out back as Peter has explained.
Cant measure either using the current system

montie · Guru

It's not that complicated!

Whenarewethere · Guru

50% full water tanks are not ideal either.

We only have a car but do try to get the mass in the centre & as low as possible but there is not a lot we can do with the second spare wheel & fuel on the roof.

Whenarewethere · Guru

montie wrote:
It's not that complicated!

Unfortunately there are too many brainless people who forget that they are actually even towing anything!

Amigo1 · Member

Agree with all of the above. Pity you can't program brains and commonsense towing habits into a spreadsheet!

Programming yaw and roll inertia into a spreadsheet based on load distribution is likely possible, but is a bit out of my non-engineering competence. Hard to program but easy to feel when towing, even with minimal experience (and brains!).

At least the present analyser might assist some people to get a few of the fundamental compliances right before they 'navel gaze' at driving habits and towing experience.

Peter_n_Margaret · Guru

montie wrote:
It's not that complicated!

Bath University in the UK have probably done more research on caravan stability than any other organisation in the world.

They think yaw stability is a critical factor.

Cheers,

Peter

Amigo1 · Member

Correct, Peter .... as you may have already seen, the video at the link below, put together following long term joint research by Bath University and Baileys in the UK well illustrates caravan stability and snaking factors, using quite a cool little model. The 4m 26s of a video like this should be compulsory viewing (among other education and testing ) if ever "Licensed to Tow a Caravan" became a motor vehicle driver's licence category.

http://www.caravantimes.co.uk/video/makes/bailey/bailey-towing-simulator-shows-how-to-load-your-caravan-correctly-$21384351.htm

montie · Guru

Some simple practical advice.

1) Your vehicle towing capacity should ideally exceed your van ATM.

2) Tug GVM should exceed van ATM by at least 10%

3) Measured ball download should be 10% approx of the measured van weight or 10% of ATM.

4) Stability control device mandatory on all new vans.

5) Tow Ed course compulsary for first time vanners.

6) Maximum speed limit for caravans 100kph.

Eaglemax · Guru

I know my rig is out of the ordinary but I have one confirmation about yaw inrtia Peter mentioned. My home made van built very light atm 998kg 16x7ft has a towball load of 85kg. Behind the single axle the 7feet of caravan that end weighs about say 300kg. Yes 7ft of caravan weighs 300kg being full ensuite, wardrobe and half a kitchen, steel tube frame. Make no mistake its built strong. Recently at low speed in a deserted safe place I tested the rigs stability by trying to initiate sway. It wasnt possible. Obviously Im not adding speed nor vacuum between passing rigs/trucks but regardless when on a main road it is solid as a rock including during side winds...why? Low C of G (van has 4" drop axle) floor 400mm from ground, roof height 2300mm. In fact being ultra light and large for its weight, my major concern is that it could more easily- blow away when parked in heavy winds so tie down points are incorporated. So from my angle you'd understand my regular quizzing as to why many caravans have a tare beyond 2300kg. So why are caravans so heavy? Simple-heavy materials. Chipboard, mdf, laminex, full size fridge, the list goes on. Why arent light weight materials used? Cost. Lightweight Fallata ply weighs half the weight, triple the cost is one example. Large wheel/tyres, twin axles etc So concluding, if caravanners were suddenly towing a van weighing 1800-2000kg atm only, instead of maxxing out their towing capacity we'd have far less rollovers. Thats my thoughts but I'm no expert.

Joda · Senior Member

Have to agree with Eaglemax here, years ago We had a 18ft. Tandem axle York towed by a 1967 v8 xr fairmont, never had any dramas, drove at 95 most of the time, tare of this van was 1150kgs due to its aluminium frame, cupboard doors & internal furniture were of thin ply, had double bed & 2 bunks, I now have a 16.5ft. Poptop that tares at 1650kgs mainly because of the heavy internal build, We could take some lessons from Euro vans, John.

Amigo1 · Member

Hi All,

I do appreciate the feedback given so far on this subject.

I have done a v2.0 (and I hope final version) of the Caravan Weights & Masses Analyser which now integrates calculations on another critical aspect of the subject that I had omitted from spreadsheet v1.0, that is the effect on your tow vehicle's front and rear axle loads caused by Tow Bar Overhang or TBO. It is a weight factor that some it seems do not consider either on purpose because it likely highlights non-compliance and restricts their GVM (head in the sand approach?) or simply because of unawareness. I hope the spreadsheet might assist the latter group but I doubt much will influence the former.

My thanks to yobarr for his kind suggestion to also cover this aspect of compliance.

Feel free to test the analyser and let me know if something seems to calculate incorrectly. Lengthy IF, AND, & LOOKUP formulas in Excel all became a bit of a haze as the night wore on!

Cheers

-- Edited by Webmaster on Sunday 18th of August 2019 08:52:22 AM

Peter_n_Margaret · Guru

montie wrote:
Some simple practical advice.
1) Your vehicle towing capacity should ideally exceed your van ATM.
2) Tug GVM should exceed van ATM by at least 10%
3) Measured ball download should be 10% approx of the measured van weight or 10% of ATM.
4) Stability control device mandatory on all new vans.
5) Tow Ed course compulsary for first time vanners.
6) Maximum speed limit for caravans 100kph.

All valid points to deal with the inherent instability of a trailer towed with an overhung hitch, but nothing that seeks to reduce that fundamental instability.

1. Yaw inertia reduction by concentrating the load over the axles.

2. Reducing the hitch overhang by getting it closer to the axle and choosing a longer wheel base tug to reduce the overhang to wheel base ratio.

3. Increasing the draw bar length to put the trailer wheels further back.

Addressing the above points individually can make a significant improvement. Addressing them all can make a dramatic improvement.

Cheers,

Peter

Whenarewethere · Guru

Does one really need to overtake. Better late than dead on time!

T1 Terry · Guru

A few yrs back, a brand new tow vehicle and caravan lost control on the Mt Ousley hills (near Wollongong) sending the tow vehicle up over the concrete barrier and destroying both vehicles. Lucky the concrete barrier was there, real carnage would have occur if it wasn't. The cause was later blamed on the way the water tanks were plumbed, all the water drained from the rear tanks into the front tanks increasing the tow-ball weight to the point the steering was controlled by the caravan rather than the driver and sent the front of the tow vehicle up and over the wall.
Often wonder how many times caravan roll overs could have been caused by a similar thing happening, but once it is scattered across the road it would be very hard to determine.

T1 Terry

montie · Guru

T1 Terry wrote:
A few yrs back, a brand new tow vehicle and caravan lost control on the Mt Ousley hills (near Wollongong) sending the tow vehicle up over the concrete barrier and destroying both vehicles. Lucky the concrete barrier was there, real carnage would have occur if it wasn't. The cause was later blamed on the way the water tanks were plumbed, all the water drained from the rear tanks into the front tanks increasing the tow-ball weight to the point the steering was controlled by the caravan rather than the driver and sent the front of the tow vehicle up and over the wall.
Often wonder how many times caravan roll overs could have been caused by a similar thing happening, but once it is scattered across the road it would be very hard to determine.

T1 Terry

Terry how you going 'ol mate?

If the residue is scattered across the road and the van plated ATM exceeds the tug towing capacity what assumptions do you think the accident investigators will make and more importantly the insurance loss adjuster?

Certainly a red light for closer scrutiny I would suggest at best.

Peter_n_Margaret · Guru

It may surprise you Monty, but I suggest that accident investigators don't make assumptions. That is pure scare mongering BS.
Cheers,
Peter

montie · Guru

Peter_n_Margaret wrote:
It may surprise you Monty, but I suggest that accident investigators don't make assumptions. That is pure scare mongering BS.
Cheers,
Peter

So they weigh the residue?

That is the only way they can determine a real outcome. An insurance company is always looking for a reason to withold payment of a claim in which case it is up to the claimant to prove them wrong. Why would anybody take that risk.

Peter, just because it doesn't agree with your view does not mean it is "scare mongering"

yobarr · Guru

T1 Terry wrote:
A few yrs back, a brand new tow vehicle and caravan lost control on the Mt Ousley hills (near Wollongong) sending the tow vehicle up over the concrete barrier and destroying both vehicles. Lucky the concrete barrier was there, real carnage would have occur if it wasn't. The cause was later blamed on the way the water tanks were plumbed, all the water drained from the rear tanks into the front tanks increasing the tow-ball weight to the point the steering was controlled by the caravan rather than the driver and sent the front of the tow vehicle up and over the wall.
Often wonder how many times caravan roll overs could have been caused by a similar thing happening, but once it is scattered across the road it would be very hard to determine.
T1 Terry

Good point Terry.After determining that this could/would cause all sorts of balance issues,I fitted taps to the inlets and the outlets of all 6 of my water tanks.(420 litres total) This means that I can maintain a reasonably consistent ball weight,no matter how much water I have on board.Cheers.

T1 Terry · Guru

montie wrote:
T1 Terry wrote:
A few yrs back, a brand new tow vehicle and caravan lost control on the Mt Ousley hills (near Wollongong) sending the tow vehicle up over the concrete barrier and destroying both vehicles. Lucky the concrete barrier was there, real carnage would have occur if it wasn't. The cause was later blamed on the way the water tanks were plumbed, all the water drained from the rear tanks into the front tanks increasing the tow-ball weight to the point the steering was controlled by the caravan rather than the driver and sent the front of the tow vehicle up and over the wall.
Often wonder how many times caravan roll overs could have been caused by a similar thing happening, but once it is scattered across the road it would be very hard to determine.

T1 Terry
Terry how you going 'ol mate?
If the residue is scattered across the road and the van plated ATM exceeds the tug towing capacity what assumptions do you think the accident investigators will make and more importantly the insurance loss adjuster?
Certainly a red light for closer scrutiny I would suggest at best.

Hi Monty, long time no hear, could be the result of my excommunication from that other forum :lol:

At best you would possibly determine total weight, but not weight distribution and that was the real cause of the accident, weight transfer for the rear of the caravan to the front of the caravan. In this case I believe there were 4 water tanks, 2 across the axles, two mounted towards the front. On the down hill run the water transferred to the front tanks increasing the ball weigh sufficiently to affect the tow vehicles ability to steer due to weight transfer from the from axles to the rear axle. Basically, nose up resulting in loss of control. I think the book writer was involved with supporting evidence for the legal battle.

T1 Terry

T1 Terry · Guru

yobarr wrote:
T1 Terry wrote:
A few yrs back, a brand new tow vehicle and caravan lost control on the Mt Ousley hills (near Wollongong) sending the tow vehicle up over the concrete barrier and destroying both vehicles. Lucky the concrete barrier was there, real carnage would have occur if it wasn't. The cause was later blamed on the way the water tanks were plumbed, all the water drained from the rear tanks into the front tanks increasing the tow-ball weight to the point the steering was controlled by the caravan rather than the driver and sent the front of the tow vehicle up and over the wall.
Often wonder how many times caravan roll overs could have been caused by a similar thing happening, but once it is scattered across the road it would be very hard to determine.
T1 Terry
Good point Terry.After determining that this could/would cause all sorts of balance issues,I fitted taps to the inlets and the outlets of all 6 of my water tanks.(420 litres total) This means that I can maintain a reasonably consistent ball weight,no matter how much water I have on board.Cheers.

Not absolutely sure on the one involved in the accident, but I have had vans in here with roughly the same tank set up so it seems likely it was a similar set up error that caused the problem. All the tanks were linked with the large diameter filler hose at the bottom and daisy chained from one end to the other, yet each tank had its own overflow.

The first climb up Mt Ousley is long and steep, so the water would have drained to the rear most tank, overflowing onto the road and partially emptying the forward tanks, then a short down hill followed by another long uphill climb. The steep down hill where that accident happened would have allowed the water to return to the front tanks, but drained the rear most tank. A combination of bad weight distribution and inexperienced operator resulted in a loss of control where the tail wagged the dog. The filler was at the bottom of the tank because the outside fill point was near level with the top of the tanks, so no way to actually fill the tanks without the water rushing back out the filler.

The 2 water tanks in our Hino have a similar problem, the right had tank fills but the left hand tank filler point is higher so the water tends to run back out the filler rather than into the tank. Took some complicated plumbing to sort the problem, the breather from the r/h tank into the top of the left hand tank and the l/h tank breather out to under the bus. A snap on hose fitting screws into the filler so both tanks can be filled, otherwise only the r/h tank fills. Not ideal but it works, both tanks are located over the rear axle so weight distribution is side to side rather than front to rear.

T1 Terry

Whenarewethere · Guru

Gas tanker spheres have to be 97% full of less than 3% empty (for return fuel) when on the open sea or they will flip over in rough seas.

T1 Terry · Guru

That would make sense, fuel tankers are a real handle to drive when half full and freezer trucks with swinging meat are even worse when cornering.

T1 Terry

montie · Guru

The first thing any new vanner needs to determine is water tank positioning and their positive or negative effect on ball download.

Tanks positioned in front of the axle group will impose weight on the ball when they are filled. Full tanks behind the axle group will have the opposite effect.

Water tanks positioned over the axle group are ball weight neutral.

Ball weight needs to be measured with tanks full, half full and empty to arrive at the ideal ball download. Many vans need to have full tanks while travelling whilst others need to be empty depending on positioning.

All vanners need to know the ideal situation with tanks and ball weight before they set off.

Mamil · Senior Member

Boat water and fuel tanks have internal baffles to prevent a 'sloshing' effect induced by wave motion from making them unstable. It would appear to me that trailer sway is similar, and the sloshing motion of water in the tanks could exacerbate the sway. Maybe RV water tanks should have internal baffles as well?

montie · Guru

Mamil wrote:
Boat water and fuel tanks have internal baffles to prevent a 'sloshing' effect induced by wave motion from making them unstable. It would appear to me that trailer sway is similar, and the sloshing motion of water in the tanks could exacerbate the sway. Maybe RV water tanks should have internal baffles as well?

To my knowledge most do.

Peter_n_Margaret · Guru

Commercially made plastic water tanks which make up 99% of the tanks used in caravans don't have internal baffles, because the manufacturing processes used (blow moulding or rotomoulding) can not put them in. It is possible to include them into plastic welded or S/S fabricated tanks, but they are much more expensive.
My solution was to use smaller tanks and several of them. Each has an easily accessible tap which selects it for use. This allows full control of where the water comes from and when.
Cheers,
Peter

T1 Terry · Guru

montie wrote:
The first thing any new vanner needs to determine is water tank positioning and their positive or negative effect on ball download.
Tanks positioned in front of the axle group will impose weight on the ball when they are filled. Full tanks behind the axle group will have the opposite effect.
Water tanks positioned over the axle group are ball weight neutral.
Ball weight needs to be measured with tanks full, half full and empty to arrive at the ideal ball download. Many vans need to have full tanks while travelling whilst others need to be empty depending on positioning.
All vanners need to know the ideal situation with tanks and ball weight before they set off.

That is really what it all boils down to, the system being capable of maintaining the water separate in each tank and the operator understanding the need for controlling water tank filling to establish the desired ball weight without adding weight to the van rear to counteract the weight added in front of the axles. It isn't just about ball weight, it is also about minimising the weight behind the axles so a pendulum effect on either axis can't start to build momentum.

One axis, front to back, will cause the porpoise effect that often causes travel sickness for the co driver and can even lead to loss of steering control if it gets bad enough.

The other axis is side to side, the rear goes left while the front goes right, then the whole thing is reversed but with a bit more momentum. The van being heavier than the tow vehicle the tail starts to wag the dog. We have all seen/experienced this one the most but often don't understand why it is happening where it never did before.

Basically, if you need to add weight in front of the axle to gain the desired ball weight, removing half of what is required from behind the axle and adding it in front of the axle will give the best result as far as handling goes.

If you need to remove weight, don't add weight to back of the van, you need to move the excess weight to between the axles.

Fine tuning involves how far forward or behind the axle the weight is, the closer to the axle the better the handling will be.

Just typing that reminds me why I drive a motorhome :lol:

T1 Terry