Is this common issue, or is this a problem ?

Whenarewethere · Guru

RE: Is this common issue, or is this a problem ?

RobDor · Veteran Member

montie wrote:
RobDor wrote:
Ok, for those interested, this is where I stand. I have spoken to an engineer at length, who does these ATM upgrades and from his advice, this is what is possible. The current cruisemaster suspension would need an upgrade from 2.6t to 2.8t, and that is possible at a cost of $1800, new arm each side, new shocks, new springs, new cruisemaster spec plate. The certifier said that all other items seem fine to handle the extra load - brakes, tyres, chassis, chains, hitch etc. Millard also verified chassis is well within spec to handle this. Certifier cost to check and provide mod plate $450. So, up to me now if I want to spend the money and upgrade, or use one water tank when travelling and manage it that way. Cheers
Rob,
If I were you I would try managing the 400kg available payload in the first instance and monitor how that works out as I posted earlier.
The Cruisemaster upgrade only gets you an additional 200kg at cost of $1800 and a further $450 for the ATM upgrade. That IMO would be your last resort.

Yep, fair call. The Mrs is telling me the same thing actually ! so, will give that a go. Thanks all

RobDor · Veteran Member

Here's an update. The first weighbridge was wrong ! as suspected, the towball weight is actually 280 and not 320 as first advised.......really annoying, chasing something that wasn't there, which I suspected. They also had the vehicle weight wrong, which amplified the problem a bit more. I have double checked with 2 other sources, and correct ball weight is/was 280. The Van ATM is actually 2660kgs. So, i dumped one of the water tanks and re-weighed, result is GCM of 5170, ATM of 2570, GTM of 2300, Ball Weight of 270. What I can't understand is if I dumped supposedly 127 litres (probably a bit left in tank), I only gained 90kgs on ATM ?? I actually don't think the tank fully emptied. But, I'm under ATM limit of 2600 and well within GCM limits, so I can even move a couple more things to the car. I can even shed another approx. 38kgs from the van if I want to upgrade the 2 x AGM batteries, for Lithium ones, they are probably nearly due anyway. Good exercise and don't believe cowboy operators...............

oldbloke · Guru

RobDor wrote:
Here's an update. The first weighbridge was wrong ! as suspected, the towball weight is actually 280 and not 320 as first advised.......really annoying, chasing something that wasn't there, which I suspected. They also had the vehicle weight wrong, which amplified the problem a bit more. I have double checked with 2 other sources, and correct ball weight is/was 280. The Van ATM is actually 2660kgs. So, i dumped one of the water tanks and re-weighed, result is GCM of 5170, ATM of 2570, GTM of 2300, Ball Weight of 270. What I can't understand is if I dumped supposedly 127 litres (probably a bit left in tank), I only gained 90kgs on ATM ?? I actually don't think the tank fully emptied. But, I'm under ATM limit of 2600 and well within GCM limits, so I can even move a couple more things to the car. I can even shed another approx. 38kgs from the van if I want to upgrade the 2 x AGM batteries, for Lithium ones, they are probably nearly due anyway. Good exercise and don't believe cowboy operators...............

Is it possible they are 95Liter tanks? They are perhaps the most common.

RobDor · Veteran Member

oldbloke wrote:
RobDor wrote:
Here's an update. The first weighbridge was wrong ! as suspected, the towball weight is actually 280 and not 320 as first advised.......really annoying, chasing something that wasn't there, which I suspected. They also had the vehicle weight wrong, which amplified the problem a bit more. I have double checked with 2 other sources, and correct ball weight is/was 280. The Van ATM is actually 2660kgs. So, i dumped one of the water tanks and re-weighed, result is GCM of 5170, ATM of 2570, GTM of 2300, Ball Weight of 270. What I can't understand is if I dumped supposedly 127 litres (probably a bit left in tank), I only gained 90kgs on ATM ?? I actually don't think the tank fully emptied. But, I'm under ATM limit of 2600 and well within GCM limits, so I can even move a couple more things to the car. I can even shed another approx. 38kgs from the van if I want to upgrade the 2 x AGM batteries, for Lithium ones, they are probably nearly due anyway. Good exercise and don't believe cowboy operators...............
Is it possible they are 95Liter tanks? They are perhaps the most common.

Can only go by the specs I was given by Millard. 2 x 127 litre water tanks as per attached pic.

oldbloke · Guru

Well, if the tap is at the bottom of the tank I'd say they are 95s. You could check using a tape measure.

RobDor · Veteran Member

oldbloke wrote:
Well, if the tap is at the bottom of the tank I'd say they are 95s. You could check using a tape measure.

Yep, I just measured 930 x760 x 180. So, definitely 127 litres.

KevinJ · Senior Member

I measured the volume of my tanks recently using a perfectly calibrated 20 litre jerry can. I calibrated it by using a 5 litre jug I have for home brewing. I poured 1 litre of water in the jerry can and marked it on the side of the jerry can. Then I poured 5 litres at a time in the jerry and marked each time till I had 16 litres. I then emptied the jerry can and then poured 2 litres of water in the jerry can and marked on the side. Then I poured 5 litres at a time in the jerry and marked each time till I had 17 litres. I continued this process for 3, 4 and 5 litres. Marking the jerry can this way is the most accurate. A bit like using a tape measure on a piece of wood. Then from the jerry can, I filled the 2 caravan tanks after opening all taps to prevent air pockets. Both tanks were full at the 164 litre mark so each tank took 82 litres. The dealer says there are (2 x up to 95 litre) water tanks. Note the careful use of their words Up to.

Are We Lost · Guru

Presumably you lift the jerrycan onto a platform or something and then use a syphon. If you had to hold it up high and pour, that sounds like hard work.

While it sounds useful to have an accurately calibrated jerry can, I think using a hose can be quite accurate enough. Using your marked jerrycan (or other marked container), run the hose at a slow to medium rate and time how long it takes. A slow flow rate helps to stop air pockets. If you want, adjust the flow so it is easy to calculate (say 5 litres a minute). Repeat to ensure you have a consistent flow rate. Then just time how long it takes to fill the tanks with the hose.

You could speed it up by doing the first 100 litres at a faster rate.

Maybe your method may be more precise but the above is plenty accurate enough for me.

KevinJ · Senior Member

You are correct. I use a step ladder with a couple of 50 x 100 x 800 hardwood timbers as the bench which I counter lever into the step ladder, under one side of the step and over the step on the other side. I have a tap on the jerry can so can control the flow through the short hose. Incidentally, I have the same markings on my grey water jerry can so I can measure how much I have used which I log on a paper chart. I don't trust the electronic water tank meter.

-- Edited by KevinJ on Friday 16th of July 2021 02:23:01 PM

iana · Guru

Calculating Tank Volume.jpg

This is the method I used to calculate the caravan tank volumes, worked for me!

yobarr · Guru

iana wrote:
This is the method I used to calculate the caravan tank volumes, worked for me!

Hmmmm. Interesting formula,which possibly is the same one that people use when trying to convince themselves that many of the popular twin-cab utes can safely tow 3500kg ATM,when that is impossible.Cheers.

oldbloke · Guru

I did similar to Kevin ( calibrated bucket) but measured what came out via the drain as it was pumped into the kitchen sink.

KJB · Guru

yobarr wrote:
iana wrote:
This is the method I used to calculate the caravan tank volumes, worked for me!
Hmmmm. Interesting formula,which possibly is the same one that people use when trying to convince themselves that many of the popular twin-cab utes can safely tow 3500kg ATM,when that is impossible.Cheers.

Amazing Formula as it always seems to come up with the answer you want - if you have already bought the ute and van ......

RobDor · Veteran Member

oldbloke wrote:
I did similar to Kevin ( calibrated bucket) but measured what came out via the drain as it was pumped into the kitchen sink.

You got me curious. I might just do the exercise and measure what comes out ..just to be sure. It may not be fully emptying

oldbloke · Guru

RobDor wrote:
oldbloke wrote:
I did similar to Kevin ( calibrated bucket) but measured what came out via the drain as it was pumped into the kitchen sink.
You got me curious. I might just do the exercise and measure what comes out ..just to be sure. It may not be fully emptying

From memory the 2x95s filled I got about 175ltrs. Just 10 or 15 litres short.

KevinJ · Senior Member

I wouldn't use the formula suggested as there is a clear error in it. Two thirds down in the middle where they say cos^2 alpha + cos^2 beta + cos^2 gamma, it should say sin^2 iota + cos^3 kappa + tan^2 upsilon. That would make more sense.

Roachie · Member

montie wrote:
As already explained not many (if any) engineer's would certify an ATM upgrade above the Axle Group Rating because any excess ball weight would render the van illegal.

An ATM of 3000kg with an Axle Group Rating of 2800kg has a margin of only 200kg ball weight to stay legal.

Most engineers ,like me, would see that as pushing the envelope of safety.

Having said that I know at least one manufacturer who plays the Russian roulette game where they rely on ball weight to comply with AGR.

Agreed. Not only that, but in practice, on the road, the van will pitch fore/aft, so that at times there will be no/minimal weight bearing down on the towbar. This means that, at those times when the van is pitching UP at the front, the WHOLE weight of the van will effectively be resting on the axle group for seconds at a time....in the same way that as it pitches DOWN, the weight on the towbar is effectively increased for seconds at a time.

If the axle group is rated to a maximum of 2,800kg and the ATM is 3,000kg, then it wouldn't take much for the loading on the axle group to vary between 2,600kg and 3,000kg at any given point in time.

Hope that's not too confusing.

Are We Lost · Guru

I'm no expert, but surely the ratings would be designed to take such fluctuations into account. Actually, the effect of hitting a bump would be many times greater than what you refer to ..... often enough to bottom the suspension. And if the van pitches forwards, the towball load may well increase dramatically, thus overloading the tow vehicle rear axle and causing the front end to lift further, reducing grip.

While these dynamic loads are rarely mentioned, they can make a very substantial impact on handling.

yobarr · Guru

Roachie wrote:
montie wrote:
As already explained not many (if any) engineer's would certify an ATM upgrade above the Axle Group Rating because any excess ball weight would render the van illegal.

An ATM of 3000kg with an Axle Group Rating of 2800kg has a margin of only 200kg ball weight to stay legal.

Most engineers ,like me, would see that as pushing the envelope of safety.

Having said that I know at least one manufacturer who plays the Russian roulette game where they rely on ball weight to comply with AGR.
Agreed. Not only that, but in practice, on the road, the van will pitch fore/aft, so that at times there will be no/minimal weight bearing down on the towbar. This means that, at those times when the van is pitching UP at the front, the WHOLE weight of the van will effectively be resting on the axle group for seconds at a time....in the same way that as it pitches DOWN, the weight on the towbar is effectively increased for seconds at a time.
If the axle group is rated to a maximum of 2,800kg and the ATM is 3,000kg, then it wouldn't take much for the loading on the axle group to vary between 2,600kg and 3,000kg at any given point in time.
Hope that's not too confusing.

Hi Bill.Until now,I have refrained from comment on Montie's post above,but since you've now commented,I would like to say that,assuming Montie is talking about one of the 3 compliance plates I posted photos of,perhaps he has simply misread the figures? When this van had an axle rating of 2800kg, the ATM was actually 3080kg,or 10% more than axle group rating.Your comments make a lot of sense,but the two modified compliance plates I have posted both have ATM above axle group rating.This is not uncommon,from my experience.Cheers

-- Edited by yobarr on Saturday 17th of July 2021 07:25:15 PM

oldbloke · Guru

Are We Lost wrote:
I'm no expert, but surely the ratings would be designed to take such fluctuations into account. Actually, the effect of hitting a bump would be many times greater than what you refer to ..... often enough to bottom the suspension. And if the van pitches forwards, the towball load may well increase dramatically, thus overloading the tow vehicle rear axle and causing the front end to lift further, reducing grip.

While these dynamic loads are rarely mentioned, they can make a very substantial impact on handling.

100%. That's why engineers build in a safety margin and why companies like Ford have test tracks.

montie · Guru

It is illegal to exceed the ATM rating of the van and it is also illegal to exceed the Axle Group Rating.

Any van that has an ATM exceeding AGR is totally reliant on ball weight to stay legal. It is not illegal however, for the ATM to exceed AGR and a very small number of manufacturers, who shall remain nameless, push the limit to maximise payload.

No engineer that I know of would certify an ATM upgrade that exceeded the AGR and it is certainly something that I would not recommend.

Most manufacturers use the Axle Group Rating (which is an engineered rating) as a basis for setting the ATM. There is not much engineering involved.