What Is Car Chassis?- Definition, Types, and Function

What is An car chassis?

A chassis is the load-bearing framework of an artificial object, which structurally supports the object in its construction and function. An example of a chassis is a vehicle frame, the underpart of a motor vehicle, on which the body is mounted; if the running gear such as wheels and transmission, and sometimes even the driver’s seat, are included, then the assembly is described as a rolling chassis.

In most passenger cars through the middle of the 20th century, a pressed-steel frame of the vehicle’s chassis formed a skeleton on which the engine, wheels, axle assemblies, transmission, steering mechanism, brakes, and suspension members were mounted.

The body was flexibly bolted to the chassis during a manufacturing process typically referred to as body-on-frame construction. This process is used today for heavy-duty vehicles, such as trucks, which benefit from having a strong central frame, subjected to the forces involved in such activities as carrying freight, including the absorption of the movements of the engine and axle that is allowed by the combination of body and frame.

In modern passenger-car designs, the chassis frame and the body are combined into a single structural element. In this arrangement, called unit-body (or unibody) construction, the steel body shell is reinforced with braces that make it rigid enough to resist the forces that are applied to it.

Separate frames or partial “stub” frames have been used for some cars to achieve better noise-isolation characteristics. The heavier-gauge steel present in modern component designs also tends to absorb energy during impacts and limit intrusion in accidents.

The Chassis has the following functions.

  • Supports or bears the load of the vehicle body
  • Provide the space and mounting location for various aggregates of vehicle
  • Supports the weight of various systems of the vehicle such as engine, transmission etc.
  • Supports a load of passengers as well as the luggage
  • Withstands the stresses arising due to bad road conditions
  • Withstands stresses during braking and acceleration of the vehicle

Examples of use

In the case of vehicles, the term rolling chassis means the frame plus the “running gear” like engine, transmission, driveshaft, differential, and suspension. An underbody (sometimes referred to as “coachwork”), which is usually not necessary for the integrity of the structure, is built on the chassis to complete the vehicle.

For commercial vehicles, a rolling chassis consists of an assembly of all the essential parts of a truck without the body being ready for operation on the road. A car chassis will be different from one for commercial vehicles because of the heavier loads and constant work use.

Commercial vehicle manufacturers sell “chassis only”, “cowl and chassis”, as well as “chassis cab” versions that can be outfitted with specialized bodies. These include motor homes, fire engines, ambulances, box trucks, etc.

In particular applications, such as school buses, a government agency like National Highway Traffic Safety Administration (NHTSA) in the U.S. defines the design standards of chassis and body conversions.

An armored fighting vehicle’s hull serves as the chassis and comprises the bottom part of the AFV that includes the tracks, engine, driver’s seat, and crew compartment. This describes the lower hull, although common usage might include the upper hull to mean the AFV without the turret. The hull serves as a basis for platforms on tanks, armored personnel carriers, combat engineering vehicles, etc.

In the intermodal trucking industry, a chassis is a type of semi-trailer onto which a cargo container can be mounted for road transport.

Types of Chassis

Following are the types of chassis:

  • Ladder Frame Chassis
  • Backbone Chassis
  • Monocoque Chassis
  • Tubular chassis
Types of Chassis

1. Ladder Frame Chassis

One of the oldest chassis, the ladder chassis gets its name from the shape of has which simply put, is like a ladder. It has two long and heavy beams which are supported by two short beams. The main selling point of the ladder chassis was how easy it was to manufacture.

During the beginning of the era of the automobile, technology was not really advanced and the simplicity of the ladder chassis made it easier to mass-produce. The chassis also makes the car assembly easier. The ladder chassis is quite heavy and thus still finds use in vehicles that need to tow heavy stuff around.


  • Easier to assemble as parts can be easily put in.
  • Construction method makes it quite tough.
  • Easier to fix as parts are not permanently attached.


  • The ladder chassis has a weak torsional rigidity making it bad for cornering.
  • Heavyweight makes it not ideal for sports cars or hatchbacks.

2. Backbone Chassis

It also gets its name from how it’s constructed. A rectangular cross-section cylindrical tube through the middle of the chassis that connects the top and the bottom suspension.

The backbone. It’s present in cars like Skoda Rapid and DMC DeLorean. The cylindrical tube actually covers the driveshaft thus making it safer from getting damaged which can also be a disadvantage.


  • Due to its construction, the half axle has better contact with the ground when off-roading.
  • The driveshaft is covered by the chassis makes it more likely to survive off-roading.
  • The structure has good torsional rigidity allowing it to withstand more twist than ladder chassis.


  • The driveshaft repair is complicated if it fails as the main chassis covers the entire shaft which makes it necessary to open it.
  • The manufacture of backbone chassis is quite expensive which increases the cost of cars it is in.

3. Monocoque Chassis

A unibody structure, it too gets its name from its structural look. Monocoque being french for ‘single shell’ or a ‘single hull’. The monocoque was first used by ships and then by airplanes. It took quite some time to figure out that they can be used in cars as well.

A monocoque is a shell around the car made by using both chassis as the frame in a single construction. This is the most commonly used chassis right now due to the number of advantages of has over the other two chassis.


  • It’s safer than both the other chassis due to its cage-like construction.
  • The chassis is easy to repair as well.
  • It has superior torsional rigidity.


  • The chassis is obviously heavy as it’s both the frame and chassis as one single entity.
  • Producing it in small quantities is not financially feasible and thus it cannot be used for cars that are not mass-produced.

4. Tubular Chassis

Tubular chassis were mainly used in race cars due to the unrivaled safety they provide. These were an upgrade from the ladder chassis as they were three-dimensional and were stronger than the ladder chassis. They employed the use of a strong structure below the doors to get more overall strength. Tubular chassis are rarely used on passenger cars.


  • Better rigidity compared to other chassis in the same weight.
  • Offers the best weight/rigidity ratio allowing the car to be lightweight while being strong.
  • Best choice for race cars due to lightweight and better rigidity than other chassis.


  • Tubular chassis are complex structures and cannot be made using autonomous methods.
  • Tubular chassis are time-consuming to build and cannot be mass-produced.
  • Not feasible to be used on passenger cars.
  • The structure raises the door which makes it difficult to access the cabin.