All you need to know about your caravan chassis

Your chassis is your caravan's skeletal foundations. It's what everything else relies on to hold your pride and joy together; the base for everything you love about caravanning and the structure that keeps you and your belongings safe from the harsh ride of the road. A good chassis is a bit of engineering brilliance.

Like many clever inventions, the principles followed by lightweight chassis designers are simple. Admittedly, the use of computer calculations to verify their performance is more complex but let’s keep to the simple details.

We all realise that a sheet of typing paper is easy to flex – until it’s rolled into a tube. That increases its rigidity, its bending resistance and so on. Similar principles are adopted when axle tubes are formed.

As regards lightweight chassis side members, these are not tubular but the all-important fold backs on the upper and lower edges give the sheet metal material a huge resistance to flexing forces compared with a flat sheet of the same material.

Punching apertures along a steel member reduces weight, but lessens strength as well. So each aperture also has a fold back on its perimeter to maintain the rigidity, too. Then there’s a matter of geometry...

How does it all fit together then?

On old-style chassis, the A-frame that gets linked to the tow hitch is also strengthened by a welded cross member that coincides with the front wall of the caravan.

Towing on poor road surfaces can break the welding points where the cross member meets the A frame members. That doesn’t happen on a modern chassis because its only cross member is the axle tube (or twin-axle tubes).
 

If you look at the main longitudinal chassis members on an AL-KO or BPW chassis, they also run in a continuous straight line all the way from the coupling head to the outermost ends of the axle tube.

That ensures that the pulling force from a towcar’s towbar transfers directly to the extreme ends of a caravan’s axle. You don’t need a degree in physics to appreciate the wisdom of this arrangement. Add these points together and the principles behind today’s chassis designs don’t merely save weight, they maintain strength as well.

What not to do when it comes to your chassis

You must never elevate a modern caravan by placing a jack under a side member. That can easily cause damage. It’s a disgrace that some service workshops completely disregard this warning.

Both AL-KO and BPW make the position quite clear, and if you don’t have a factory-fitted side jack, you normally have to position a portable jack at the outer-most ends of the axle tube. Always check the manufacturer’s instructions before undertaking any work.
 

Looking after your chassis

As it has to be protected from everything the road can throw at it, the chassis of a caravan has to be given a process of corrosion avoidance, but it's also necessary to give it a bit of love at least once a year.

Every modern chassis, such as those produced by AL-KO, is hot dipped galvanised to create a thoroughly protective coating. During bad weather, however, salt deposits from the road will need to be cleaned off to ensure that this coating remains effective in the long run.

AL-KO say: "it is recommended that the chassis/components are washed off, using a pressure washer on an annual basis (especially after winter usage), to avoid undesirable build up of salt and dirt deposits."

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