Single Axle and Twin Axle
On a single-axle caravan the entire axle load is carried through one axle; on a twin-axle caravan this load is shared between two axles. A twin axle provides higher mass capacity and more stable behaviour on the road, but it has a cost in manoeuvring and tyre wear.
The difference between the two layouts is not only capacity; load distribution and support geometry change as well.
- Capacity: with the same tyre and bearing class, a twin axle allows a markedly higher total mass.
- Stability: the distance between the two axles creates resistance against rotation about the vertical axis and reduces sway.
- Manoeuvring: in tight turns the tyres scrub sideways and wear increases.
- Tyre failure: on a twin axle a deflating tyre does not by itself put the vehicle on the ground, but excessive load falls on the other tyre.
In terms of levelling, the difference is in jack placement. On a single axle the vehicle turns easily about the axle; because the lever arm is long, the front and rear jacks change the angle with little stroke. On a twin axle the body is longer and stiffer, and the jacks are placed ahead of and behind the axle group. In both cases keeping the rectangle formed by the jacks as large as possible lowers the load shares.
Context in which this term is used: Guide to automatic RV levelling