Why pay extra for Disc Brakes, Air suspension in off road caravans?

kimberley off-road caravans blog header Tandem Drum Brake comparison air suspension disc brake off road caravans

When it comes to an off-road caravan's suspension there is a big gap between "bells and whistles" and "core essentials". Start by looking underneath to see the big differences.

The image on the left shows the contrast of suspension (and braking) systems. Conveniently they are completely colour coded red and blue! Lets look at the 2 contrasting systems. The Blue system is by Kimberley and fitted to an off road caravan with a tare weight of 2.7 tonnes. The red system is from another manufacturer with a plated "axle load" of 3.49 tonnes. The Suspension system comprises the wheel (and tyre), the brake hub, the suspension arm, the spring and the shock absorber. In some units there is an anti-sway bar (visible in the blue system).
Item Red System Blue System
Travel Height Fixed Travel height Adjustable travel height. This means that by lowering the caravan when on the highway, you get better fuel consumption as well as stability.
Off road manouvres Fixed height means limited off road manouvres (like a reverse turn with ditches either side, Adjustable height for different off road requirements. An Auto-ride height controller can be used to match vehicle height! Revolutionary reverse turns may require very high height.
Wheel Alignment Adjustable toe-in for optimum handling and maximum tyre life Adjustable toe-in for optimum handling and maximum tyre life
Brakes 12 inch Drum Brakes Electric Activation  12 inch Disc Brakes Hydraulic operation, electronic activation
 Parking Brake (not visible) Lever arm that activates mechanical wire that operates front tandem wheels only. One touch button that electrically activates the disc brakes that are then locked into parking mode by valve. All 4 discs are locked on.
 Spring Coil Spring short travel  Air Spring long travel
 Trailing Arm  Rear Swing, steel, trailing arm  Rear Swing, steel, trailing arm
 Shock Absorber  Twin Tube inside Coil  Monotube externally mounted
 Chassis  e-coated  Hot dipped Galvanized with either Alloy of galvanised sub frame.
 Over-travel prevention  Chain and protective cover  Tripple sewn straps
 Anti-Sway  None visible  18mm Anti-sway bar
Warranty and/or Quality Assurance None Listed 5 Year Warranty of Chassis and suspension arms that is transferrable to a second buyer.
Electric Wire Join for electric brakes resized 600Lets start with the brakes. The red suspension system shows the drum brakes with electric activiation. These are the bigger "12inch" drum brakes and there is an "off road" protection plate added to the inside. The photo on the right is a close-up of the red suspension.  It shows the electric activation wire from the magnet/ drum brake assembly (white) coming out of the back of the drum brake. It is "joined' to a black activation wire that runs to the trailer plug. The join is surrounded by black electrical tape and it is held in position with the cable tie. Drum brakes have these disadvantages:
  • They fade
  • They perform poorly when wet
  • They are heavy and add to the "unsprung weight"
  • They require regular maintenance
  • They reply on an electrical wire for activation
  • And the most difficult issue: The hand brake is a mechanical level that requires quite some presure.
Drum bakes have these advantages:
  • They are easy to add to install
  • They are low cost
The Blue image shows the Disc Brakes which have:
  • Less than half the weight of the drum brakes
  • More than twice the stopping performance.
  • Easy to change a disc pad
  • No fading and fast recovery when wet
  • And a big issue: The parking brake is a one touch operation that locks the 4 disc brakes solid as a parking brake.
Then we examine the spring and shock absorber. The red system has coil springs and a reputable brand of Twin tube shock absorber. There is a separate blog on the remarkable differences between twin tube and the mono-tube shock absorbers in the blue Kimberley system on the right.
Item Red System Coil/ Twin Tube Shock Blue System Air spring/Mono-tube shock
Travel (up and down vertically) A very short travel system Approximately twice the travel distance as measured.
 Performance in high heat generation when travelling over corrugations The heat is disipated in the shock absorber which needs maximum air flow. Any obstruction like the springs and cups in the red system will deteriorate performance. The shock absorber has a free and clear air for maximum heat disipation.
 When camping off road To change the caravan level, wheel ramps and chocks are required. To change the caravan level, simply adjust each air bag with a finger controlled valve until level.
 Variable rate for the big bumps?  No, fixed spring rate  Yes, variable spring rate with increase at bottom of compression stroke
Then finally the chassis and anti-sway system
Item Red System Blue System
Chassis e-coated Hot dipped galvanized which provides best protection inside the RHS sections which sre NOT visible on outside
Anti-sway None listed Anti-sway bars are added for safety stability with the air suspension in the unlikely effent the air bag ruptures or leaks when cornering
These are the individual components. When they all go together, the entire system has 2 very important factors for off road use:
  1. The travel height of the suspension has to be both high but also to have greater suspension travel than traditional caravans
  2. The unsprung weight of the suspension has to be the absolute lowest possible. This is a determining factor in caravan stability.
To read more on this subject consider these blogs or eBooks:
Suspension Design for off road caravan Best stability in an off road caravan
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