Double axle caravans

Regulations state how high the towball shall be and there is normally (offroad vehicles excepted) no way of adjusting that height.

It is important that the noseweight is set an adequate level, regardless of whether the trailer is a single or a twin axle. Just below the lower of the two plated figures for the towbar and trailer is normally the target that one should aim for.

Consequently, when towing, the rear wheels of a twin axle will always be carrying a slightly higher load than the front pair.

The best way to attain the correct nose weight is just a balancing act of where to position things inside the caravan, safely, for towing.  We always like our noseweight to measure around 100kgs (the maximum limit for both our car's tow ball and the caravan hitch), and it's never been a problem to reach that.  It may be different for you depending on your towing vehicle and caravan layout. 

Balancing a twin axle is just the same as a single axle, yes it is just as easy to get a nose weight that is too much, but mine does not seem as sensitive to noseweeight variance and tows well with a nose weight anywhere between 80kg & 100kg. Although it can be a challange to get it that low.

Surely towing slightly nose down is the norm so the rear axle will carry slightly less load than the front

That would only be the case if the hitch would have to be pulled down to align with a lower towball, but that would mean a negative noseweight.

I don't see that!

When the caravan is level and set up for 0 nose weight each axle would be carrying the same load and the centre of gravity would be between the two wheels (caravan balanced on it's axles! = no jockey wheel needed).

As the caravan is loaded to generate a nose weight the centre of gravity moves forward. If the hitch is then allowed to move down  on to a tow ball the caravan adopts a slight nose down attitude and to achieve this  the front axle suspension compresses (takes more load) and the rear axle suspension is extended (taking less load).

But a twin axle caravan will not necessarily be standing level if no noseweight is applied. It may already have a nose down attitude when its centre of gravity is exactly half way between the two axles..

I don't understand the concept of "applying" a nose weight, the nose weight is the amount of weight the nose exerts when the caravan is loaded.

In an ideal world we would tow level with equal load on each axle.

I think it will be standing level. the suspension units (4) are the same and bolted to a solid chassis rail, the wheels (4) are the same, tyre pressures are the same. If the centre of gravity is exactly half way between the wheels how would it not be level. 

As the caravan is loaded with weight towards the front, the centre of gravity moves forward. If the centre of gravity moves forward the caravan must adopt a nose down attitude, it can only adopt a nose down attitude by compressing the front suspension more than the rear, hence my original assertion that the front axle is taking more load than the rear if the caravan is nose down. 

In the above scenario there will however be zero nose weight (nose hanging in free space) until the caravan reaches tipping point, this happens when the centre of gravity moves forward of the front wheels, at this point the nose will crash to the ground unless something stops it. Ideally that something is a nose weight scales so that you can carry on loading the caravan until the nose weighs 100kg (or as required).

I'm lost

You know what they say if you can't blind them with bull