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What is a chassis and what does it do?

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Updated 12 Oct 2019

Jason Unrau

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On the outside, a car’s shiny painted exterior hides its true strength.

And no, it isn’t a high-horsepower engine squeezed in under the bonnet.

Any vehicle’s toughest, strongest attribute rests in its chassis.

What is a chassis?

The word ‘chassis’ is a direct translation from French, meaning ‘frame’.

For vehicles, it’s the main support structure upon which everything is built.

There may be some people who include in the definition other systems that are attached to the frame such as axle assemblies, brakes, wheel hubs, suspension components, and even the drivetrain.

However, the purest, simplest explanation is simply to think about the chassis as the vehicle’s frame.

Types of chassis

Two different styles of chassis dominate the field: a ladder-style body-on-frame chassis and a unibody chassis.

A body-on-frame chassis is often made from square steel tubing welded together to form an extremely strong framework.

It’s the basis for nearly all pick-up trucks and commercial vehicles, as well as some utes.

Classic cars also use a body-on-frame design to support the powerful engines and heavy weights they carry.

A unibody chassis is formed from stamped metal sheets and body parts connected together.

There isn’t an independent frame – the stamped metal parts that are welded, bolted, glued, and screwed together give the chassis the strength that it needs.

Parts could be made of aluminium, steel, reinforced plastic, or even carbon fibre. And typically, a unibody chassis is used for efficient vehicles and weight reduction.

Why does a car need a chassis?

Every car, ute, or truck is made of thousands of parts.

Many need a strong, rigid structure upon which to fasten these parts.

Whether unibody or body-on-frame, a chassis is the foundation of everything in a car build.

The engine is fastened into the chassis with motor mounts. Body panels are bolted to the chassis to hold their shape.

Axle assemblies, wheel hubs, rack and pinion, suspension shocks and springs, windscreen wiper motors, and even seats mount directly to the chassis.

It holds parts securely in place and creates the solid structure that you depend on for safety, especially in a collision.

What problems can happen?

There isn’t much to go wrong with a chassis on its own, but outside influences can have a dramatic effect.

Two things in particular can affect a chassis:

  • Corrosion, commonly called rust, deteriorates a chassis’ strength and rigidity over time. It’s particularly noticeable in high moisture areas and coastal communities. It’s especially bad because it can be hidden for years.
  • Physical damage, such as a car collision, can compromise a chassis’ strength. Today’s vehicles are manufactured with crumple zones. A serious impact could render a chassis unrepairable. Or, an off-roading adventure could stress the chassis and crack it, often without your knowledge!

You can find the best mechanic for a chassis inspection on
AutoGuru. We’ve got awesome mechanics near you!

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Written By

Jason Unrau

Jason is a Canadian automotive content writer with a background in the auto service industry, but he’s been hooked on cars and mechanics since childhood.

One of his first cars was an ’80 Mazda RX-7 that’s sorely missed to this day. A ’68 Ford Torino GT, a ’66 Ford Country Squire Woodie station wagon, and a ’96 Suzuki GSX-R 750 have spent time in his fleet of cars, bikes, and trucks over the past two decades.

Jason’s pride and joy is under construction – a turbocharged ’88 Mazda RX-7 convertible. Also on his resume is CASCAR official certification.