What Is A Car Chassis vs. Car Frame vs. Car Platform?

Unless you are a mechanic, car enthusiast, or auto hobbyist, there'd be no reason for you to automatically know the difference between a car's:

• Chassis
• Frame
• Platform

In fact, you may use the terms interchangeably or not understand the nuance when a person chooses one term over the next. The terms are very different, however, and there are perks to telling them apart.

From better understanding any repairs a mechanic recommends to having a good view of how your car operates (and which parts of it may need servicing), these terms can be a valuable addition to your vocabulary.

So what are the differences between each term, and what is a chassis after all?

What Counts As A Car Chassis?

Originally, the word "chassis" was used broadly, referring to the entire skeletal structure of a car. However, the term has split off in modern times.

In a technical sense, the chassis now refers specifically to the load-bearing part of the car's frame. This is the horizontal section that supports and connects all the important components of the car. If we were to strip away everything else, the chassis would look something like this photo:

What Is A Car Frame?

While the chassis is the load-bearing part of the frame, the "frame" itself is now defined as the rest of the structural body of the car. This is what you imagine when you think of cars being put together on assembly lines; the frame is the skeletal outline of a car.

While the average car's body isn't significantly load-bearing (except in cases such as armoured vehicles), it is still a vital part of the whole structure. It's responsible for managing all of the normal forces exerted on the vehicle. These may include:

• The effects of acceleration
• Sudden braking
• Wind speeds
• Dealing with impacts
• The shock cause by things such as hitting potholes

In early designs, vehicle frames and chassis were joined by bolting them together, in what is usually called a "body-on-frame" construction. This creates a relatively flexible body, as the nuts-and-bolts fixtures will always flex more than a weld would.

This slight flexibility is still beneficial for modern, heavy-duty vehicles, because of the huge loads they have to carry. The design provides enough cushioning in the system, so that it stops parts from cracking due to pressure.

More modern passenger cars, however, are constructed with a 'unibody' design, which is a single, welded body design. This has less flex than a body-on-frame construction, but it's considerably safer as a passenger car.

That's because body-on-frame designs used to break at all the fixtures when they crashed – so even relatively low-impact crashes would cause serious harm to passengers. Unibody frames, however, are designed to account for impacts. Since the whole frame is welded together, the force of an impact can be spread throughout the whole body. As such, fewer things break and the car is more likely to buckle than to split.

What Is A Vehicle Platform?

The term "vehicle platform" (sometimes interchanged with "frame") is found in vehicles such as the Ford Mini Platform or the Nissan MS Platform. This is a more ambiguous term than "chassis" and "frame", because it doesn't refer to a specific part of the car. It's actually a set of shared design and manufacturing elements.

Because it's so expensive to research and develop a car design, manufacturers will often pool resources in order to research a particular type of car. The research will then go into developing a frame, suspension, engine, exhaust, and transmission system that can have different body trim and interiors added.

Essentially, the fundamentals of a car can be sent to a manufacturer as a complete construction, or as a complete guide. Each manufacturer can then add their own design touches to it.

This is partly why modern cars look so similar - but it also lends itself to greater fuel efficiency and safety standards. New advancements in assembly and fabrication technology also mean that manufacturers can use some elements of a platform, but make changes to a body design far more easily.

Now that you understand the difference between a car chassis, frame, and platform, you can better approach how your car works, know the designs that will suit your needs best, and request any adjustments it may need from a mechanic.