Axle Position

JOSHG · Member

Axle Position

yobarr · Guru

JOSHG wrote:
Hi everyone. I post a topic the other day about lower towball weights on a single axle van. It has the storage capacity to bring the ball weight up to what ever is needed. To further that post I need some advise regarding axle position. The single axle van I'm looking at seems to have the independent suspension pretty much centered,maybe slightly to the rear of the main van body. I have seen others with the wheel a little further back but this usually increases the tare towball weight. If I can increase the ball weight to approx 8-10% of the van weight does it matter if the wheel is a little more centered. Or as the distance from wheel to rear might a be a touch more than others this could still get a sway up. Sorry for the odd question, I am new to caravanning and just looking for the right one.

First off, could I congratulate you on being so responsible with your weights.

Most vans seem to have their axles, or axle group, slightly behind the mid-point of the chassis. This helps with achieving the generally accepted towball weight of 10% of ATM for safe towing.

The most important thing is to get heavier items right over the axles.

Remember that your rear overhang must be no more than 3.7 metres, and must also not exceed the front load space.

Beware the current trend on single axle vans to have the axle towards the rear, with the bed East/West at the front as there often is major problems with towball weight with this setup.

Recently I spent much time sorting the weights on the van of a lady who was "doing a lap" with a small car towing a too-heavy van that had its axle very well behind centre of chassis.

Took me two days to get it all legal from its waaaay overloaded towball, with the removal and disposal of the McHitch that she was convinced she 'needed' being my first step, as this unit is very heavy and also increases towball overhang, the effects of tiwball weight on the car's rear axle, and the effects of yaw.

Depending on your van's ATM your desired 8-10% towball weight should be acceptable, but once your ATM gets up over about 2000kg it becomes more important that towball weight be around 10% of ATM.

Without getting too technical at this point, if safety is of any importance to you, ALWAYS the weight on the wheels of the car should be at least 10% greater than the weight on the wheels of the van.

There is much I could add, but the above will get you started. Any further questions are welcome. Good luck! Cheers

-- Edited by yobarr on Friday 23rd of February 2024 09:14:56 PM

JOSHG · Member

Hi yobarr, thanks for the reply. The vans I'm looking at are just the Chinese hybrid variety. But I have found one that is a little lighter at tare 2190kg with a ball weight of approx 140-160kg. Atm is 2990kg. Most of the storage available is forward of the wheels, so I guess I can add to this to achieve 8-10% when loaded. Most are 2400kg tare with 200-230kg ball weight. I don't really want 300-320kg. The van just seems to have the wheel just shy rear of centre. I hope if I buy it I can have my 8-10% on the ball and not have any sway. I do agree there are many single axle vans with the wheel well behind center, but creates a high towball weight.

PeterD · Guru

The axle position under a van depends a lot on the layout of the van. Those with a kitchen at the font of a van will have the axle near the centre and be able to easily achieve a 10% ball weight. If the kitchen is across the rear (as many of the small vans have) the axle will appear too far back. It is the kitchen that contains the heavy items like the oven and fridge. Have another look at vans and see what the layout is and where the axle is located. If the kitchen is over the axle and the axle is in the centre, be very suspicious of the van having a light ball weight.

JOSHG · Member

A couple of photos to show axle position. Kitchen and fridge are forward of the wheels

PeterD · Guru

With the "Kitchen and fridge are forward of the wheels" I would not want the unloaded ball weight to be too heavy, particularly with that large storage box on the front.

JOSHG · Member

Meaning that by the time you fill the front box, fridge extra the loaded ball weight would be very high.

Are We Lost · Guru

JOSHG wrote:
Meaning that by the time you fill the front box, fridge extra the loaded ball weight would be very high.

Not necessarily. From the photo I could not see where the fridge is positioned. Presumably it is about 90 litres (i.e. not full height). You would be unlikely to load that with more than 20kg of food and drinks. If it is half way between axle and coupling, that would mean 10kg added to the towball weight from filling it. If looking at a van it is easy to measure and do that calculation.

With the toolbox you would need to take more care because it is close to the coupling. So the majority of what you put in there will be added to towball weight ... maybe 80%. The positioning of water tanks is important because water typically weighs more than all the other stuff combined. If there is one tank forward of the axle and one behind an equal distance, and they are joined they will make negligible difference to towball load when full or empty. If there is only one tank, and it close to the axle, it might make 10-15kg difference on towball weight between full and empty.

Then take into account whatever else you carry and where it will be stored. The weight of all that you carry does soon add up, but as these are likely spread through the van, and not so heavy, they should not make a large difference.

So, it may be that the empty towball load is a little too low. Maybe you could tune the weights according to what you carry in the front boot and toolbox as you intially posed.

If at a dealer ask them to show you the weight as displayed with a towball scale (note that these are often not very accurate). You can then calculate from there.

-- Edited by Are We Lost on Monday 4th of March 2024 04:17:27 PM

PeterD · Guru

That should bring your ball weight up to a reasonable percentage figure. I like to use 10% as a minimum and not the maximum ball weight for Oz designed vans.

JOSHG · Member

Hi everyone, to give you an idea on van and tow vehicle weights. Not sure if it will change anyone's advise. Still considering ordering the van so only what's stated on website

Van Nomadic 16ft bunk
Tare 2190kg Atm 2990kg Towball 145kg

Tow vehicle
2021 Hilux Sr5 dualcab
Suspension upgrade NOT GVM
Gvm 3050kg Gcm 5850kg Weight 2480kg
Certified weighbridge on car, full fuel, tub of 4x4 gear in rear, no towball weight, no passengers.
Estimated weight
Passengers 240kg,
Towball 250kg
Ideally keep towball weight to approx 250kg or starts to become bum down / nose up

Total 2970kg only leaves 80kg for added gear.

JOSHG · Member

I am just still concerned about it swaying.
If i have 2 vans. Both have a loaded towball weight of say 250kg which is approx 8-10% of atm for both vans. But the wheels of 1 van are more centered to the body the other the wheels are more towards the rear.
Could one potentially sway more than the other.

Or as this one has a lower tare towball weight.even though most storage is forward of the wheel, If I load it up to say 8-10% but it still isn't enough to precent sway.

Maybe I am working about nothing. Just a big investment if it doesn't work out.

-- Edited by JOSHG on Monday 4th of March 2024 11:04:26 PM

PeterD · Guru

If you have a good percentage of weight on your tow ball, it means that the centre of gravity of the van is a good distance in front of the axle. That is really what counts. Have a read of this article - Caravan and tow vehicle dynamics.

JOSHG · Member

Hi Peter,
Thanks for that link. Interesting read.
Talking to some owners they say the van seems to travel ok.
As you have mentioned and others, it does come down have a decent towball mass, loaded sensibly etc.

It has been hard to find a van that ticks all the boxes, especially when the new hilux has such a low gcm. Really are restricted to finding a lighter van, big bunks, semi off road/ off road. Moat are just too heavy for the hilux.

Are We Lost · Guru

How much stuff did you have in the back when you took it to the weighbridge? Does it have a canopy or drawers, fridge, etc? 2480kg by itself sounds a lot.

Where most enquiries about weight run into difficulties is with rear axle loading, and I am suspecting you are heading that way. Do you have separate weights for front and rear axles, and what is the Hilux rear axle rating? You said 240kg passengers ..... what weight will be in the back seat?

The Hilux has a reasonable wheelbase of 3085mm, but the rear overhang is a bit more than desirable. My guess is it will be about 1400mm from axle to towball. Using calculations, if you have 250kg ball weight, that will add over 360kg to the rear axle by itself. So I suggest you check into this aspect very carefully.

As for your concern on the axle position and sway, the answer is "it depends". Following on from Peter's comment and a skim of the article he linked, it is the weights and relative loading that matter. The most important thing to avoid is weight at the rear end of the van. Next is weight at the front, but much less critical than at the rear. If a gust of wind perhaps from a passing truck pushes the van sideways a little, any weight on the rear will tend to become like a pendulum as the van pulls back into line. If sway does start to develop it is much easier to keep in contol if the weight is central. So avoid weight at the ends, particularly the rear. And the closer any such weight to the axle, the better.

I am assuming gas bottles go in that front locker. Two full bottles are around 40kg and unlikely to be included in the Tare or the quoted towball weight. Even with that answered, I would not rely on the quoted weights. Anything fitted after leaving the factory would be unlikely to be included in Tare.

As it appears you are very close to limits, I suggest you really need to be KNOW how this will work out when laden for travel with full water tanks. The position of those tanks are critical. Get the dealer to help with ACTUAL measurements to avoid a very costly mistake.

-- Edited by Are We Lost on Tuesday 5th of March 2024 12:58:15 AM