I read that the new Suzuki Jimny has a "ladder frame" chassis. What does this mean? Is this a better type of chassis in terms of durability, maintenance and reliability?
The term "ladder frame" came about because the base structure resembles a ladder. In the early days of motorcar production, the construction method was basically a body bolted onto the ladder frame on which the engine, drivetrain and suspension are all mounted. It was then the best way to produce a car based on existing technology and machinery.
Currently, almost all commercial and some off-road vehicles like the Jimny are constructed in this manner.
With vans, trucks and buses, the body-on-frame method offers the flexibility to bolt on different body styles. For example, either a single-or double-cab with different loading beds behind could be mated to a single chassis model used to build a pick-up.
For a dedicated off-roader like the Jimny, the ladder frame offers the high ground clearance and extensive wheel articulation suited for rough terrain. The body and chassis are separate, which also makes it easier to repair in the event of any chassis damage during off-roading.
The ladder chassis, however, is not used in most passenger car production today because the ladder has to be made strong enough to take all the suspension load and, at the same time, support the body and mechanical components.
This results in a frame that is far heavier than an equivalent unitary body construction where the chassis and body are basically one.
Also, the ladder frame lacks the structural stiffness for good dynamic characteristics at speed. The unitary body is more rigid, which is good for high speed handling, grip and road holding.
The unitary (or monocoque) body is lighter and stronger and offers sufficient production flexibility for different body styles.