Does jack placement change on single-axle and twin-axle caravans?
The number of jacks is 4 on both types; what changes is the position. On a single axle they go far from the axle, on a twin axle near the chassis ends.
The number of jacks does not change: on the KTS200 it is fixed, and in both cases 4 units of D3501-1142 are used. What changes is the position of these jacks on the chassis. A single-axle caravan stands on one line of support along its front-rear axis, so the jacks have to come far enough from the axle; on a twin axle the load is already spread over two lines, front-rear oscillation is small and the jacks can be brought closer to the chassis ends.
What changes on a single axle
Single-axle caravan: The vehicle balances on a single axle line and behaves like a see-saw along the front-rear axis. For this reason the front and rear jacks must be placed far enough from the axle, yet at points the chassis can carry. If the jacks are positioned too close to the axle, the force needed for front-rear correction increases: as the lever arm shortens, the same angular correction asks for more force. Raising the front jacks also directly changes the noseweight; the load distribution has to be checked before you uncouple.
What changes on a twin axle
Twin-axle caravan: Since the load is spread over two axles, front-rear oscillation is smaller; placing the jacks close to the chassis ends improves both stabilisation and left-right correction. Against that, the area between the two axles is crowded with pipes, tanks and brake gear. The practical consequence of the single and twin axle difference during installation is that there is less freedom of placement on a twin axle: a point that looks suitable often falls exactly over a tank or a brake pipe.
Decision table
| Criterion | Single axle | Twin axle |
|---|---|---|
| Number of jacks | 4 | 4 |
| Front-rear oscillation | Pronounced | Small |
| Distance of the jacks from the axle | As far as possible | Close to the chassis ends |
| Governing constraint | Lever arm | Density of gear under the floor |
| Sensitivity to noseweight | High | Lower |
Checks to make before placement
- The mounting point must be a chassis rail or a reinforced area specified by the manufacturer; the detail is explained under choosing the mounting point.
- Clashes with the fresh water tank, the grey water tank, the exhaust and the cable and pipe runs must be measured first.
- With the jack in the retracted position, check its height above the ground and the risk of striking something on the road; ramp entrances are where this most often causes trouble.
- The position of the inclination sensor is independent of the jack placement but should be settled in the same plan; where the ASX103 is to go affects measurement accuracy.
- Do not lift all wheels off the ground; jacks are no substitute for a parking brake, use chocks.
Where these two patterns do not apply directly
- Three-axle vehicles and special chassis. The placement is worked out project by project, and the generalisation here is not enough.
- Caravans with a long rear overhang. If the rear jack comes too close to the end, the chassis twists and reinforcement comes onto the agenda. On this kind of vehicle it is safer to put the rear jack not at the very end but over the nearest cross member.
- Fixed cabins and tiny houses. There is no axle to speak of; the jacks are planned relative to the corners of the load-bearing frame. The tiny house application is covered under a separate heading.
For the exact placement, consult your caravan manufacturer or an authorised project engineer. In practice the order is this: measure the underside from end to end, mark the tank and pipe runs on the chassis with tape, fix the jack points on paper, hold the jacks in place and confirm the measurement before you bolt anything, and only then drill. Every correction made after a hole has been opened leaves a permanent mark on the chassis.
The full topic: How to choose levelling jack capacity