Feature: Caravan suspensions
Hardings Caravan Services explains what's what
Andrew Harding of Hardings Caravan Services explains the differences between each of types of suspensions available.
"The signs of wear on the slipper springs are when they start to point downwards"Caravanners are becoming more and more adventurous as the years go on. Our traditional trip to Rosebud or Merimbula at Christmas has evolved into a yearly trip around the big block – Australia.
As we embark on these intrepid travels, we probably need to spare a thought for our caravan suspensions. This is what will ensure our trip is memorable for all the right reasons. Over our 34 years at Hardings we have rebuilt, serviced and replaced many suspensions and have the experience to understand the conditions where they all best fit. For many years we supported the philosophy of ‘keeping it simple’ by using straight axle and leaf springs. This still is a very good option and the most common suspension still around, however caravanners now go where they never did before. This has led us to fitting several different suspensions in the last few years which are all tailored to the customers travel habits.
This article provides an insight into some of the lessons we’ve learnt and will help you understand your current caravan suspension as well as assist in specifying the suspension on your next caravan purchase. These are our opinions based on our experience.
AXLE AND LEAF SPRINGS (SINGLE AXLE)
A very simple system that is suitable for made and unmade road conditions. With a suitable rating on the springs and axle this system will last for many years without much maintenance at all. Springs are most commonly an eye-slipper type where the rear section of the spring slides loosely in a hanger, or on eye to eye springs like you often see on the axle of a utility.
Springs will fatten out and need replacing after 50,000km. The signs of wear on the slipper springs are when they start to point downwards (i.e., away from the horizontal direction) at the rear end of the spring. Historically, we had lots of bent and broken stub issues however this virtually never occurs these days due to axles being more appropriately rated, particularly in the stub section. If you were doing a lot of unmade road travelling then packing a spare spring may be a good asset as they can occasionally crack when used on corrugated/unmade roads.
This independent axle has come out of Europe and been installed on several Australian caravans over the years. It works on a rubberised cam system that if rated appropriately will provide maintenance-free travelling for many years. They now come fitted with shock absorbers as well, however even without shockers they don’t bounce excessively. They can be used for offroad conditions, but are probably not ideal for extensive offroad travelling. For instance, if a repair was required en-route it would be quite difficult as they are a complete axle.
In saying that, they are generally a good option and wouldn’t require attention unless overloaded. After several years/km they may need re-rubbering and the signs of this is wear on the inner edges of the tyres. Re-rubbering can only be done at Al-ko where they press in new rubbers based on the required axle rating.
SIMPLICITY SUSPENSIONS (SINGLE AND TANDEM)
When they talk about keeping it simple this suspension ticks all the boxes. A very robust but simple independent suspension system that is very durable and used on many offroad caravans. The suspension has a swing-arm for each wheel which is extremely strong to ensure long term reliability. This system comes in a single and tandem system. The tandem system is load sharing, which means it evenly distributes weight to all four wheels whatever angle the caravan may be on.
We recently serviced a single system that had just ticked over 350,000km and it appeared the original bushes were still in the swing-arms. Springs are about the only wear component plus the top bush in the tandem model. Carrying a spare spring is often worthwhile where the caravan is travelling long distances in offroad conditions. The single axle system uses a standard eye-slipper spring, an eye to eye spring for heavier applications, whilst the tandem system uses a unique leaf spring.
KNEE SUSPENSION (SINGLE AND TANDEM)
This independent suspension is mainly found on one brand of caravan in Australia. It is like the simplicity system in that it is simple plus seems to virtually never wear the moving components it uses. It doesn’t distribute the weight on all four wheels evenly so in a tandem situation it’s important to have the caravan setup level so weight isn’t falling onto the axle that has more of the caravans balanced weight.
Maintenance seems very little again apart from leaf springs that need changing when fattening out. The swing-arm on this system is different from the rest in Australia in that it hinges from the middle of the caravan, so when a spring is starting to fatten out it will wear the inner edge of the tyre. They are suitable system for some unmade road conditions although carrying a spare spring would be advisable.
TANDEM ROCKER SUSPENSIONS (TANDEM ONLY)
You may have heard and seen all our discussions on these suspensions. They are fantastic at distributing the weight evenly on all four wheels (i.e., load sharing against being independent), but in the process they wear the components at a faster rate than most other suspensions. They are probably half the price of the other independent suspensions thus they are the most common tandem suspension system around. Their downfall though is they do need more regular maintenance than most of the other systems we have discussed (every 10,000km). Carrying a spare spring with this system is strongly advised if you plan to do the odd detour on unmade roads. On a more positive note we have manufactured a special ‘low wear’ bush which extends the wear out a lot further and seems to help reduce springs breakages. We believe these bushes may take a suspension that is wearing standard bushes every 15,000km and push this out to around 40,000km. We usually recommend waiting till the bushes start wearing and then changing to the low wear bushes.
TANDEM ROCKER-ROLLER SUSPENSIONS (TANDEM ONLY)
This is a load sharing system similar to the rocker suspension, however at the end of each spring is a big loop where a roller runs in. This loop provides free play at the end of each spring for smaller axle movements, while the bigger axle movements rock on the main pivot arm like the rocker system. This difference enables this system to achieve much greater distances before wear appears and significantly decreases the risk of spring breakages. We have converted quite a few caravans over to this system to provide a better suspension for the long term in respect to spring breakages en-route and general maintenance. This conversion makes the system much more appropriate for outback touring than the standard rocker system which is quite prone to spring breakages on unmade roads. Whilst they are similar suspensions the loop in the back of this system’s springs reduce the shattering type movement which breaks leaf springs on the rocker system.
INDEPENDENT COILS (SINGLE AND TANDEM)
These suspensions have become a lot more popular in the past 10 years. The engineering on some of these suspensions is now very well designed and is probably one of the best systems for outback touring. These suspensions are often fitted to the very well respected caravans and tent trailers built specifically for offroad use. Sugar Glider has built a very reliable system for many years. The control rider system also seems to be well engineered and is now being fitted to one long standing and well respected caravan.
Coils have the advantage of being less prone to breakage than leaf springs however they do need to be assisted by shock absorbers to prevent excessive bouncing. Shock absorbers need to be monitored every 10,000km or in situations where they may sit for a few years between use. These suspensions do provide for a smooth ride for your caravan on corrugated rides and possibly don’t suffer from spring breakages like leaf springs systems.
AIR ASSISTED (SINGLE AND TANDEM)
There are a few very well respected outback touring caravans using the air suspension system which has earned a very good reputation for outback touring. Those who do a lot of outback touring and are prepared to spend a little more on there suspension would not be disappointed by an air suspension system. Customers talk about an appreciable difference on unmade roads. Trucks are progressively moving across to air suspensions and in time it’s likely the caravan industry will also make the transition. If you were installing it you would need to ensure the pipes and compressor system are well protected.
First published in Hardings Caravan Services newsletter, Winter 2009.