What Is the Chassis of a Car?
A chassis provides strength to your vehicle. Learn the basics of unibody, body-on-frame, ladder, and monocoque chassis in this brief overview.
Written by Bonnie Stinson
Reviewed by Melanie Reiff
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A chassis is the structure that bears the weight of the rest of the vehicle. It resists movement, supports the weight of the load, and offers mounting points for other components. Every type of chassis offers unique benefits.
Have you ever noticed that scary road sign that shows a truck tipping over? This sign is often placed on a roadside beside a steep grade that curves. That’s because some vehicles are more vulnerable to movement while cornering because of their chassis.
No matter which vehicle you drive, the chassis is a key component. It resists twisting and supports the rest of the body so you can navigate the road safely. But how does a chassis really work? Why are there different types of chassis, and why do most modern cars use unibody construction?
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4.7/5 rating on the App Store | Trusted by 5+ million customers and 7 million cars4.7/5 app rating | Trusted by 5M+ driversWhat is a chassis?
The chassis of a car is the sturdy structure upon which the rest of a car body is supported. Note that the frame is a part of the chassis but the two terms are not synonymous.
A vehicle chassis may hold the drivetrain, transmission system, driveshaft, differential, rear axle, front axle, suspension system, braking system, steering system, exhaust system, cooling system, and more.
Passenger cars, SUVs, off-road vehicles, race cars, trucks, and buses all need a chassis.
The chassis frame design is most common in SUVs and light trucks. However, most modern cars (especially passenger vehicles) use a unibody frame to reduce weight and achieve better fuel economy.
What does a car chassis do?
A chassis provides two very important things to your vehicle: stability and mounting points.
A chassis is a load-bearing piece that supports the weight of passengers and cargo. It also keeps the vehicle strong without distortion when cornering or carrying heavy loads. This is called torsional stiffness. For example, the transmission cross member is directly connected to the engine mount where it resists the torque to a highly specific rating. In poor road conditions, the chassis may help a motor vehicle resist twisting or even side winds.
Equally important, the chassis provides mounting points for the rest of the vehicle body. Parts like the steering wheel, suspension system, and engine are mounted to the chassis.
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Types of chassis
Here are five common types of automotive chassis design. Some types of cars generally use the same type of chassis.
Unibody
In a unibody vehicle, the frame and chassis are made as a single unit. Most modern cars, vans, and SUVs use unibody construction. There are a few unibody trucks, like the
Honda Ridgeline
and the Ford Maverick
.Unibody chassis are less heavy and give better fuel economy. They’re also the safest type of chassis.
Body-on-frame
This is the original design method for automobiles—except back in the early 1900s, they were made completely of wood!
Body-on-frame is when the chassis and frame are built separately. These structures are slightly more flexible, which is why body-on-frame is often preferred in off-road vehicles. Body-on-frame chassis can tow heavier payloads, too.
This type of chassis is commonly found in trucks and occasionally in SUVs.
Toyota
uses body-on-frame construction in many of its SUVs, like the 4Runner
and Land Cruiser
. A backbone chassis is similar to body-on-frame but it employs a strong tubular backbone to connect the rear and front suspension areas. You’ll find this type of chassis in vintage De Tomaso, Tatra, and Skoda vehicles.
Ladder frame
A ladder frame is a type of body-on-frame chassis that looks like a ladder, with two long parallel beams and shorter beams in between.
Commercial vehicles such as trucks and buses typically use a ladder chassis. Light pickup trucks and similar types of vehicles may use ladder frames, too.
The ladder frame is good for towing, but it’s not stiff enough to provide support at higher speeds—especially while cornering. This is why you won’t find the ladder frame in modern performance vehicles or
hatchbacks
.Monocoque chassis
Monocoque means “single shell” in French, and it’s a type of chassis where the external shell provides structural strength. Since it is built like a rigid cage, the monocoque chassis offers excellent protection in crashes.
You are most likely to find the monocoque chassis in sports cars, race cars, and other high-performance vehicles.
What is a rolling chassis?
A rolling chassis means that the vehicle frame is ready to roll. In other words, the car chassis already has the necessary parts attached to allow it to be driven legally on the road. This usually includes the engine, transmission, tires, and axles.
The term “rolling chassis” is most commonly used by truck and bus manufacturers to describe a chassis that they send on to the vehicle bodybuilder for completion.
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FAQs
What is the difference between a chassis and a frame?
While the words are often used interchangeably, chassis refers to the load-bearing part of the frame.
What material are chassis made from?
Today, most modern passenger vehicles use chassis made from aluminum alloys. Sports cars may use carbon composites, like carbon fiber.
Can a chassis be fixed?
Possibly. Car frame damage can sometimes be repaired by a skilled auto body shop—however, the cost is likely to be astronomical. It all depends on the extent of the damage.
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