[Deli Llama]

Ah well. There you go. Thanks for that information.

 

[gatkins]

Still Love my Touareg, I'd rather sell the van and get a lighter one!
Authorities seem to be increasing their monitoring of GVM, GCM and rear axle loading especially on the East Coast of Australia

 

[Deli Llama]

A lighter caravan would save money on fuel and help the environment.

 

[Wolfy]

True enough re a relatively low rear axle load, but that's in the context of a decent payload (GVM-tare) and a competitive towball overhang relative to wheelbase that minimises ball weight transfer to the rear axle.

But the table you posted and the vastly differing relative strengths and weakness shows just what a minefield anyone wanting to tow is entering!

 

[Wizz954]

My coilovers arrived in the post and so did the Alexgee lift kit. Unfortunately the coilovers are very different to the OEM coilovers so I won’t be able to use the Alexgee kit with them. I will be selling the kit complete with the OEM coilovers once they’re out. If anyone is in the market for shocks and lift kit, PM me.

 

[Wizz954]

My new coilovers are being fitted and hoping to get the car back today. They’ve been having difficulties with the rear ones with sketchy installation instructions. I’m having the ride height set to maximum since the lift kit won’t fit. This should give me 20mm lift which is better than nothing. I’ll be hitching up the caravan and heading up to my mates to test his Towpro brake controller on my van. I’m on another thread about that!

I’ll post pictures of the caravan hooked up with the new springs and without changing the hitch height we’ll see if it sits better with the increase in ride height and stiffer springs. Once I get the desired towball height established I’ll then look for a standard (shorter) hitch of the right height to reduce the leverage and rear axle load. It may have to be custom made.

Anyone know who makes custom hitches?

 

[Wizz954]

Small hiccup with coilovers. The damping adjusters cannot be accessed while shocks are mounted and need to drill holes in the floor 🤔
Won’t get the car back today

 

[Deli Llama]

I wonder if strengthening the springs will move the weak point to somewhere else. Will the maximum rear axle weight be increased? If so, will you be able to get an engineer's certificate to show the maximum rear axle weight is increased?

I hear that the checking of caravan weights by the authorities had increased lately. If you were to have to much weight on the rear axle you may need a certificate to prevent being fined. 🤔

 

[gatkins]

The are videos on you tube showing that adding air bags to the rear suspension, Eg additional load capacity, to level up the load actually increases rear axle load. Stiffening up the rear with bigger springs will increase rear axle load.

 

[rgh0]

All other things being equal the rear spring rate does not change the rear axle load. However stiffer springs that reduce rear sag mean all other things are not equal and will generally mean more tow ball weight as the tow ball is higher unless other adjustments are made to counter that.

cheers
Rohan

 

[Wizz954]

Interesting thoughts. I have heard Landcruisers can get GVM upgrades, I’ll look into how they get certified.
My thinking is that increased spring rates means you won’t sag as much under the same load and can therefore avoid bottoming out due to reduced travel. If that’s the limitation to rear axle load then the spring upgrade should increase GVM.
What else would limit rear axle load? Would it be the build strength of the car in some way?

 

[Deli Llama]

I not a mechanical engineer but I would image so. There're lots of things keeping the tires and the body connected. (I think)

 

[rgh0]

https://www.pedders.com.au/news/everything-to-know-about-gvm-upgrades/#:~:text=A%20GVM%20upgrade%20involves%20changing,overall%20GVM%20of%20the%20vehicle

.

useful background information in GVM increase

 

[Deli Llama]

No GVM upgrades listed there by Pedders for the Touareg. That's a pity because, as I've mentioned before, the maximum rear axle weight is the usual limiting factor on a Touareg.

 

[Wizz954]

I spoke to an engineering company that certifies GVM upgrades. Unfortunately cars with monocoque bodies cannot be recertified so we’re stuck with what we’ve got. I’ll just get the rig weighed so at least I’ll be able to work out how to stay legal.
The certification code is LS11

 

[Wizz954]

All other things being equal the rear spring rate does not change the rear axle load. However stiffer springs that reduce rear sag mean all other things are not equal and will generally mean more tow ball weight as the tow ball is higher unless other adjustments are made to counter that.

cheers
Rohan

Hey Rohan can you explain the logic behind the tow ball height and the increased tow ball weight? I don’t understand how it affects it.
Currently my rear sags a huge amount and the towball height is lower as a result. When I have my stiffer springs in, I’m hoping it will then lift the towball height to where the caravan is more level rather than nose down. In effect it should get things back to optimal tow ball height and caravan attitude. I was thinking the nose down attitude would put more weight on the towball.

 

[rgh0]

Yes unfortunately Tregs have not attracted much after market modification support from people like ARB and Pedders.

I guess it is because they tend to not be used used much off road. However they are used for towing a lot and a GVM upgrade to increase allowable rear axle load would be useful and I would have thought it would have sufficient market for someone to do it and get it certified.

cheers
Rohan

 

[gatkins]

can you explain the logic behind the tow ball height and the increased tow ball weight?

At a recent weigh-in we asked this question also of our tester.
To demonstrate the van TBM was done at 2" higher and 2" lower
The values did vary from the weight at level but only by < 5kg

I would think more significant would be if you are using the std 50mm ball you are limiting movement due to its less angular capability than a DO35 or similar

 

[rgh0]

Hey Rohan can you explain the logic behind the tow ball height and the increased tow ball weight? I don’t understand how it affects it.
Currently my rear sags a huge amount and the towball height is lower as a result. When I have my stiffer springs in, I’m hoping it will then lift the towball height to where the caravan is more level rather than nose down. In effect it should get things back to optimal tow ball height and caravan attitude. I was thinking the nose down attitude would put more weight on the towball.

If you have a dual axle van as the towball drops the weight on the tow ball will also reduce somewhat as it puts more load on the van front axle creating a countering torque and reducing the ball weight. Raise the tow ball with stiffer springs and the ball weight will tend to go up. How big the effect depends on the van and its suspension design.

cheers
Rohan

 

[Steve_L]

Not the sort of assurance that I consider be the "be all and end all", but, speaking with a caravan GVM upgrade specialist, he commented that in his experience, if the rig (car + caravan) looks level, you've got half the 'battle' with the weight police won. That of course won't save you when it comes to an insurance claim, but it may just save you the hassle of being pulled up and going thru the motions on the scales - especially if you're only just a few kgs over (and I do mean...just a few kgs)