The ladder chassis is one of the most original methods of creating a vehicle and it has its origins back about 500 years ago!
The concept of luxury personal transportation came out of a Hungarian town called Kocs – a derivative of which is now our word “coach”. It was so successful that very soon, most of Europe was using them – it did help that variously connected royal families were traveling in them.
The first coaches were built on the age old design of a wooden frame that had panels fitted to cover the important people. Typically the driver and other servants were kept outside. What the good people of Kocs did was to apply some evolution. The main focus was comfort, so the body and the chassis were split so that the chassis could have an early form of suspension to soften the rough roads.
This meant that the body sat on a frame and the wheels and later leaf springs, were connected to the frame rather than to the whole unit. The first coach-builders then focused on the luxury of the cabin. When cars started to be made, it was logical to copy the designs of horse drawn carriages, simply replacing the power unit – i.e. the horse retires in favour of the internal combustion engine. It is notable that many car names are derived from coaches and I wrote an article about the names used for convertibles recently.
The original chassis came over as a ladder chassis, so named because it looks like a ladder when laid out. This was an easy replication and meant that the bodywork could be bolted on top. Initially all chassis were made from wood, however it wasn’t long before steel replaced the wood for strength and a bit more flexibility. Importantly, steel was a cheaper and more accessible material. Manufacturers could weld flanges and other structural plates on to the steel chassis, whereas wood limited the design.
You can see from the picture above, of an early Rolls-Royce, how the chassis has the body fitted and all plumbing – fuel and brake lines are connected such that they are protected from the elements. Slung in the middle is the engine, gearbox and drive train. The concept was simple and cheap – at one end of the scale were cars like the Ford Model T and at the other, the meticulous attention to detail of the Rolls-Royce.
The drawback to this type of chassis was that the body was on top – like the earlier carriages and this made the vehicles very tall and heavy, thus limiting their performance. On the flip side, they were strong and allowed for a higher ride height needed to manage the roads.
It is for this reason why trucks and off-road vehicles retained the use of the ladder chassis long after road and race vehicles had moved to either a unitary construction or space-frame chassis. An example was my father’s Jeep CJ5 from the 1970s that had a very narrow ladder chassis similar to the Rolls-Royce pictured, with the same configuration for the engine and drivetrain. It was fitted with leaf springs that sagged and needed fixing every few years!
The backbone chassis could be considered an evolution of the ladder – a simple construction that allowed all major components to be fitted via sub-assemblies and suited the lower sports coupes which often had a lightweight composite bodyshell.