Changed from Single to Twin Axle

[TLC]

Hi,

We have just changed from a single axle to a twin axle caravan. I must report that it felt much more stable and was a dream to tow. Even though it is 4ft longer than my other caravan I didn't have any problems at all. Have just spent a few days at a CL site testing it out & it is fantastic. Ticks all my boxes!!!

 

[Lutz]

You write that your new caravan feels much more stable "even though" it is 4ft longer. I would say that it feels more stable because it is 4ft longer. A longer caravan will always be more docile than a shorter one and that applies equally to a single axle. I have a 26ft single axle and that is a dream to tow as well.

 

[Steve L]

Hi TLC.

I've had both single and twin axle vans.

Twin axles are inherantly more stable as you have 4 wheels trying to go straight ahead. You might detect a slight tendancey of reluctance to follow your car round bends, it is very minute and most folks don't feel it.

Our current single axle van (Abbey 540se) tows very well the only thing I find is that the Aalco hitchhead stabiliser doesn't stop yawing (up & down movement of the van). I would like to fit a blade stabiliser aswell, to try to help that movement.

Glad your happy and having fun.

Atb Steve L.

 

[Lutz]

Yawing is sideways movement, Steve. The up and down movement that you are referring to is pitching, but current AlKo 2004 and 3004 models have pads arranged in such a way that they are supposed to reduce pitching as well.

You say that you would like to fit a blade stabiliser in addition to the AlKo. My advice is not to because that would double the resistance to movement between car and caravan. Doubling the resistance means doubling the forces, which may then be higher than what the car and towbar manufacturer took into consideration in their designs. Industry standards for hitch type stabilisers provide for 300Nm of resistance to pitching. Any increase in resistance beyond that could result in premature failure of load carrying components.

 

[ProfJohnL]

Hello Steve,

As far as I know the blade type stabilisers only have damping in the horizontal plane, the spring load of the bar/blade is primarily there to keep the blade in the guide. It may reduce the amplitude of the pitch or change its frequency but it won't add any damping to the motion.

 

[Lutz]

A good blade type stabiliser should not be in the same horizontal plane as the towball. Otherwise it has no chance of reducing pitching. But to my knowledge, many quality proprietary blade stabilisers are offset below the level of the towball so, in theory, they should work. However, the spring load within the blade does nothing to prevent pitching as a spring itself has no damping characteristics.

 

[Steve L]

While the leaf spring might not have been designed to prevent this actio, I did find that it helped on all the other standard hitch caravans we had.

The tow car has had heavy duty dampers fitted two years ago which also helped a bit.

On my old Renault 25's I used doughnut coil spring assistors which again helped especially as the 25 was a low to the ground anyway.

 

[Lutz]

Spring assisters or heavy duty springs will change the ride height and the amplitude of pitching motion, but they do not prevent pitching. In order to prevent pitching it is necessary to increase damping, such as with heavy duty shock absorbers (and/or a stabiliser with friction pads arranged to provide damping in a vertical plane).

 

[ProfJohnL]

The most effective device for reducing pitching will be shock absorbers fitted to the caravan wheels.

 

[Lutz]

I don't quite agree with you there, JohnL. Shock absorbers on the caravan reduce bounce and hence improve adhesion to the road surface (consequently also improve stability), but they do relatively little to reduce pitching.

Keeping the payload aboard the caravan as low and as close to the axle as possible will probably do more good.

 

[ProfJohnL]

I don't quite agree with you there, JohnL. Shock absorbers on the caravan reduce bounce and hence improve adhesion to the road surface (consequently also improve stability), but they do relatively little to reduce pitching.

Keeping the payload aboard the caravan as low and as close to the axle as possible will probably do more good.

I agree that sensible loading is very effective, but as an add on component, shocks will probably have more effect than any other.