Kimberley Kruiser Chassis and Independent Suspension
Setting a new class in un-sprung weight for an off-road caravan
Suspension design requirements must include:
- Compliance to the Australian Design Rules for a caravan or trailer.
- Lowest possible “un-sprung weight” of arms, springs, shock absorbers, hubs and brakes.
- To absorb harshness in off-road travel.
- Ability to adjust toe-in for tuning tyre wear.
- Ability to withstand harshest corrugations.
- Importance of maximum vehicle control by the driver.
However, good suspension design for off-road travel is more than just the close-coupled independent suspension of the Kimberley Kruiser. It requires an aggressive focus on getting the lowest un-sprung mass of the suspension and wheel system. This is what makes Kimberley’s suspension “system” quite unique. Lets explain why.
The un-sprung weight of a wheel controls a trade-off between a wheel's “bump-following” ability and its vibration isolation. Bumps in the road cause tire compression — which induces a force on the un-sprung weight. The un-sprung weight then responds to this force with movement of its own. The amount of movement, for short bumps, is inversely proportional to the weight. A lighter “wheel/hub/brake/tyre set” which readily moves in response to road bumps will have more constant grip when tracking over an imperfect road. For this reason, lighter “wheel/hub/brake/tyre sets” are the most desirable feature in off road applications.
In contrast, a heavier “wheel/hub/brake/tyre set” (which moves less) will not absorb as much vibration. The irregularities of the road surface will then transfer to the caravan through the geometry of the suspension and hence ride quality is deteriorated. For longer bumps that the wheels follow, greater un-sprung mass causes more energy to be absorbed by the wheel/hub/brake/tyre sets and makes the ride worse.
Optimal ply rated tires that have more elasticity help by providing some springing for most of the (otherwise) un-sprung mass, but the damping that can be included in the tires does have limit considerations of speed and possibly overheating.
The shock absorbers dampen the spring motion but also must be less stiff than would optimally dampen the wheel bounce. For this reason we only use the highly responsive mono-tube design which dissipates heat at a far greater rate. The wheels vibrate after each bump before coming to rest. These motions form the “road corrugations” which we hate. It is the sustained wheel bounce in subsequent vehicles that enlarges the corrugations and deteriorates the road!
High un-sprung weight also exacerbates wheel control issues under hard acceleration or braking. Vertical forces exerted by acceleration or hard braking combined with high un-sprung mass can lead to severe wheel hop, compromising traction and steering control.
So how has Kimberley perfected such a low un-sprung mass on the “wheel set” over the last 10 years?
The first item to focus on is the wheel hub and brake assembly. The disc/brake hub we use and the PBR disc brakes are half the weight of the 12inch Electric drum alternative. Then we use lower weight Mono-tube shock absorbers, and the lightest weight performance coil springs. The bump stops and suspension straps and are our own design at the lowest possible weight. These shock absorbers are mounted in the optimum perpendicular position and use stainless steel bushes for resilience in corrugations. (If you see dual shock absorbers at an oblique angle; the units aren’t as effective in this position so 2 are used with the result of higher un-sprung mass).
Finally, the high MPA trailing arms have a unique curve pattern for the best weight/performance.
The benefit to customers is not only better vehicle control and better ride but a 5 year warranty on the chassis and the trailing arms. They are well looked after in a Kimberley!
Introduction of Advanced Air Suspension as standard for the Black caviar Model
The Black Caviar Model, has as standard, advanced air suspension replacing the coil springs with air springs. The benefit of this type of suspension is one of convenience more than a difference in ride performance. The convenience benefits of the advanced air system are:
- At campsite, the Kruiser can be levelled by simply toggling the air switches that adjust the height on each side of the Kruiser. These switches are behind the pantograpgh door on the tunnel boot on the drivers side.
- On regular highways, the travel height can be reduced to lower the unit to the ground and reduce the windage. This will improve towability and improve fuel consumption.
- In off road conditions the air springs perform virtually the same as the proven coil springs with very similar travel and performance characteristics.
- a compressor and small high pressure tank is included and can be used with the tyre inflator to adjust easily the Kruisers tyre pressures on the road!
- In the event of a flat tyre, an isolation valve above the wheel affected can be activated and the Kruiser lifted on the other 3 wheels. In most cases this should allow you to easily change the wheel!
Deflection Testing of Kimberley Kruiser Chassis
The purpose of the test is to create deflection and assess the elasticity of the chassis before the upper body unit is added. If the chassis shows signs of creep or movement then it fails the test.
The test comprises the standard Kruiser Chassis with:
- A static load of 480 kgs of water in 4 tanks on the furthermost rear point of the chassis.
- There is negative drawbar weight.
- A Dynamic load is then added with the chassis in its most vulnerable position.
- The Dynamic Load comprises 4 men at approx. 400 kgs bouncing as aggressively as possible.
- The Chassis is positioned with 2 wheels on the ground on the “off” side and one wheel elevated on driver’s side to create a worse case torsional load.
This gives a total of 880kgs load unsupported which is 5 times the “normally supported static” load at the rear end of the chassis.
The chassis is flexed then examined for any deflection when returned to the normal position.
The entire testing is video recorded and replayed frame by frame. The chassis is measured and evaluated back in the test bay at the factory.
The Chassis passed this test with flying colours and all other dynamic loading tests, travel tests, cornering tests and suspension tests.
It is great to see the enthusiasm of the engineering and build team trying to destroy what they created!
Metal protection in the Kimberley Kruiser Chassis
There are 3 principal metals used by Kimberley. 
- Hot dipped Galvanized Steel,
- 6061 or 6060 Marine Grade Aluminium and
- 304 Stainless steel.
The Chassis which includes the drawbar, the chassis rails, the suspension “hangers”, and the rear tie plate are all hot dipped galvanized.
The sub-frame which supports the floor and side rails at the base of the fibreglass is 6061 Aluminium.
The chassis and the sub-frame are fastened using hydraulically controlled 2 piece “Huck” Rivets. We use the genuine USA brand.
Trim strips and some protection plates are in 304 stainless steel.
Hot Dip Galvanizing
Galvanizing refers to the coating of steel or iron with zinc. This is done to prevent rusting. The value of galvanizing stems from the corrosion resistance of zinc, which, under most service conditions, is considerably greater than that of iron and steel. The zinc therefore serves as a sacrificial anode, so that it protects exposed steel. This means that even if the coating is scratched or abraded, the exposed steel will still be protected from corrosion by the remaining zinc - an advantage absent from paint, enamel, powder coating and other methods. Galvanizing is also favored as a means of protective coating because of its comparatively long maintenance-free service life.
The term galvanizing, while technically referring specifically to the application of zinc coating by the use of a galvanic cell (also known as electroplating), also generally includes hot-dip zinc coating. The practical difference is that hot-dip galvanization produces a thick, durable and matte gray coating - electroplated coatings tend to be thin and brightly reflective. Due to its thinness, the zinc of electroplated coatings is quickly depleted, making them less durable for heavy outdoor applications (except in very dry climates).
Corrosion with Aluminium 6061 6060
Marine grade aluminum such as 6061 or 6060 have their own built in protection. They form an oxide on the surface that excludes contaminants and prevents corrosion. The aluminum will not corrode unless the oxide is damaged or if removed for painting. When welded, a new oxide layer is formed and it is important to preserve this layer.
Stainless steel 304
The surface finish of this stainless steel is an important factor in its service life. The polished surfaces exhibit the best corrosion resistance but is less practical and generally not used. The brushed or linished surface finish used by Kimberley requires washing and cleaning to minimize maintenance. Fine red oxide ore will embed in the brushed finish and can be a source of corrosion over time if not removed with cleaning. Any salt water immersion or spray from beach travel will also require washing soon after exposure. With good maintenance, there is a long service life. Internal components made of stainless steel have a low maintenance and long service life.
Corrosion Protection with Dissimilar Metals
The compatibility of two different metals may be predicted by consideration of their "Anodic Index". This parameter is a measure of the electrochemical voltage that will be developed between the metal and gold. To find the relative voltage of a pair of metals it is only required to substract their Anodic Indexes.
For normal environments, such as storage in warehouses, there should not be more than 0.25 V difference in the "Anodic Index".
For harsh environments, such as outdoors, high humidity, and salt environments, there should be not more than 0.15 V difference in the "Anodic Index".
Often when design requires that dissimilar metals come in contact, the galvanic compatibility is managed by finishes and coatings.
For the high durable galvanized steel and aluminium alloy combination, a layer of polyurethane is used in between the surfaces. The 2 piece “Huck“ steel rivets used have a Anodic Index difference of only 0.10 to the alloy. There is a tight steel to steel fit through the chassis web for a 0.05 difference.
This principal has been used now since 2005 on the Alloy front frame and Gullwing boxes on the Kimberley Kampers with excellent results. There has been no evidence of corrosion between the 2 surfaces over the 7 years of use that has ever been seen or reported. The rivets used in the Kamper are a lighter grade but the principal applies.
Anodic index Reference click here |
|
Metal |
Index (V) |
Most Cathodic |
|
Gold, solid and plated, Gold-platinum alloy |
-0.00 |
Rhodium plated on silver-plated copper |
-0.05 |
Silver, solid or plated; monel metal. High nickel-copper alloys |
-0.15 |
Nickel, solid or plated, titanium an s alloys, Monel |
-0.30 |
Copper, solid or plated; low brasses or bronzes; silver solder; German silvery high copper-nickel alloys; nickel-chromium alloys |
-0.35 |
Brass and bronzes |
-0.40 |
High brasses and bronzes |
-0.45 |
18% chromium type corrosion-resistant steels |
-0.50 |
Chromium plated; tin plated; 12% chromium type corrosion-resistant steels |
-0.60 |
Tin-plate; tin-lead solder |
-0.65 |
Lead, solid or plated; high lead alloys |
-0.70 |
2000 series wrought aluminum |
-0.75 |
Iron, wrought, gray or malleable, plain carbon and low alloy steels (Huck rivets) |
-0.85 |
Aluminum, wrought alloys other than 2000 series aluminum, cast alloys of the silicon type |
-0.90 |
Aluminum, cast alloys other than silicon type, cadmium, plated and chromate |
-0.95 |
Hot-dip-zinc plate; galvanized steel |
-1.20 |
Zinc, wrought; zinc-base die-casting alloys; zinc plated |
-1.25 |
Magnesium & magnesium-base alloys, cast or wrought |
-1.75 |
Beryllium |
-1.85 |
Most Anodic |
Ballina May 2012
