long A frames? what does it do?

[giovanni_5060838]

got a burstner, and noticed that the A frames are quite

alot longer than those on the in laws ect.

Checked the towball weight after fitting the two gas bottles

and some other bits and found the weight to be about 60kg.

Was expecting it to be higher and as the caravan has a max of 1500kg and the galaxy a towball weight max of 85kg was really

aiming for 80ish kg.

FIRSTLY. what can i do about getting the weight further up?

BAR putting the awning right at the front,and would that be

enough.

SECOUNDLY. why do some vans have such long A frames ?

I understand how the longer it is the more leverage principle,

but what are the other merits/demerits.

thanks..

 

[Lutz]

The longer the A-frame, i.e. the greater the distance between coupling and axle, the more stable the caravan is likely to be.

Be thankful that you have an inherently low noseweight because it is a lot easier to increase the noseweight without adversely affecting stability than it is to reduce it.

 

[rob_jax]

Hi Giovanni,

The longer A-frame has benefits in easier manoeuvring (especially reversing) and the potential for better resistance to side-wind deflections, but the big benefit is increased stability and lower nose-weight.

The reason a caravan needs nose-weight is to counteract the effect of wind on the front (top edge) of the caravan. The effect of the wind pushing on this edge is an attempt to rotate the caravan around the wheels, lifting the A-frame and the tow coupling.

Increasing the nose-weight increases the speed at which the caravan loses this battle (and hence increases the stability).

Alternatively fitting a long A-frame means that exactly the same stability can be achieved with a lower nose-weight.

Our Eriba Triton has a MTPLM of 1200 kg and a long A-frame, we normally tow with a nose-weight of 35kg.

Robert

 

[Guest]

My van has the longer A frame, about 50 mm according to the brochure. As stated it does relieve the strain on the towball and allows?? you to put into the front locker all that you would like. One other point I have noted is that there is obviously more space between the rear of the tow vehicle and the front panel of the van, so easier access and less chance of hitting the van if you jacknife with a wrong reverse manouever.

I suppose the downside is that for a certain shipping length you get 50mm less body length, and as 'Nicole' used to tell us, size does matter?

 

[Lutz]

An added bonus for some is added space between car and caravan, enabling one to mount a bicycle carrier on the A-frame

 

[giovanni_5060838]

Thank you very much for your replies.

Really helpfull.

Rob jax. am a bit confused on the low towball weight.

Should i be happy with 60kg, or should i have it nearer the 85

the car can handle, which is still lower than the 7% of the

caravan gross weight of 1500kg, and is often refered to by

caravan magazines as the target weight....

 

[Lutz]

The higher the noseweight the better for stability, so you'd do well with keeping it at your 85kg limit. For the same reason, I don't hold much for the 7% formula. Best to make full use of what the manufacturer's spec allows.

 

[rob_jax]

Hi Giovanni,

The University of Bath (School of Mechanical Engineering) study into caravan stability showed that there is a linear increase in stability as you increase the caravan nose-weight. So 51kg is better than 50kg, which is better than 49kg, and so on.

So I totally agree with Lutz, somewhere close to the 85 kg maximum will be "safest". But in the Bath study, they also found that the linear increase was quite small (on the limited range of caravans and tow cars they investigated) - so you may not notice any difference between 70 kg and 80 kg.

The Bath study also showed that a correctly working stabiliser (ALKO, Winterhoff or blade type) offered a significant improvement in stability - more than could be achieved by optimising the nose-weight.

So a good stabiliser and sensible nose-weight is a great start.

The only proviso is that if you are going to fill the car boot with heavy luggage, and use the maximum nose-weight too - you may want to look at the car data for the maximum permissible boot load - and make sure you don't exceed that or the rear axle maximum load.

Robert

 

[giovanni_5060838]

Again, thank you to Lutz and Rob jax.

Feel alot happier about towing the burstner now..

 

[RayS]

All good stuff above. I've got a Burstner too - the long A frame is to take a bicycle rack and your will see the standard brochure for the van shows it so fitted. i think only UK spec vans have a plastic faring rather than the rack as standard.

Bit surprised the noseweight is as low as you say. With two full gas bottles and not much else mine is near 100KG. However, I agree with Lutz that - within the limits available - the more the better and my MB goes to 135Kg. Only snag I've found is that with noseweight up around 100Kg the load on the nosewheel when using the mover makes the wheel dig in a bit.