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The Most Common Vehicle Frame Designs Today: Body-on-Frame, Unibody, Monocoque, and Space Frame

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There are plenty of different ways to build your dream car, and that starts with the frame design. Discover the various frames that suits the vehicle’s purpose.

For some people, it’s not enough to dream of driving their dream car, or even to own one of these fantastic vehicles. For true fans, building a car seems like the height of car fanhood. And to build your car, you have to start with the frame.

If you do your research properly, then you’ll encounter terms such as body-on-frame, unibody, monocoque, and space frame. It can be annoying when you read articles that seem to assume that you ought to know what these terms mean. In some cases, you may get definitions and explanations, except you’re overwhelmed by the technical jargon.

So let’s use plain English to explain what these terms actually mean:

Body-on-Frame

This is the original car frame design at the start of the emerging motorized car industry in the early 20th century. The first car makers simply got a worse-wagon, and then replaced the horse with an engine and a way to turn the wheels.

With this design, you start with the structural frame that carries the suspension and powertrain. Then you attach the body, usually using mounts that isolate the vibrations.

Ladder Frames

The simplest type of body-on-frame design is the ladder frame. The frame looks like a ladder, with 2 rails interconnected with lateral support members. This works very well for rough roads, which is what people had to deal with in the early 1900s.

You can still see the ladder frame in just all heavy-duty trucks, as well as in pickup trucks and SUVs. This type of frame offers great off-road capability, and its strong enough to work with towing loads.

Skateboard Chassis

This is a low-profile chassis with the fully-integrated powertrain and suspension. You can then attach other components to this chassis.

This is the frame that works very well with electric vehicles. The low-profile motors and batteries of EVs match the low-profile chassis. From there, you can then attach the fuel cell, batteries, and hydrogen tanks with 4 in-wheel motors.

Check out the Model S from Tesla, and you’ll find a version of this skateboard chassis in the frame design.

Unibody

This time, you have a single structural piece combining the major chassis structural support with the body, along with the floorboards and the crash-protection components. All these disparate elements are joined together by molding, bonding, or welding.

This type of frame is a lot more complicated to design and build, but in return you get a stronger frame. You can then go for the usual strength and enjoy considerable reductions on the weight of the vehicle.

That means you get better fuel efficiency and improved handling, which is why this is the typical frame design you get in most cars and crossovers. Basically, if you want a more comfortable vehicle, you need a unibody for the build.

Monocoque Chassis

This is a much rarer frame design, but it’s virtually the standard design for race cars. The frame is similar to the exoskeleton of an insect. The “skin” of the car is also a structural piece, as it bears tension and compression loads.

The monocoque first came out in the 1962 Lotus 25 Formula 1 race car, which used aluminum. McLaren improved on this in 1981, when they used composite alloy reinforced by carbon fiber for their monocoque chassis.

McLaren uses this type of frame design for their cars, since every McLaren production car is basically a supercar.

Space Frame

This time, the “skeleton” of the car bears most of the load, while the “skin” of the car bears very little of the load. The skeleton in this case is usually an internal framework of metal tubes, while the exterior bodywork is the skin.

In other words, the design is virtually the exact opposite of the monocoque chassis. Yet ironically, this is also a popular frame design for racing cars.

The Porsche brand came out with the first space frame in 1947, when it appeared on the Porsche Type 360 Cisitalia. However, it was the 1959 “Birdcage” Maserati Tipo 61 that really made the space frame popular.

The tubular space frame construction method makes for easy racing car manufacturing in small volumes. It’s no trouble to weld the structure, as you don’t need pricey stamping presses and welding jigs.

Conclusion

Let’s sum it all up, with the right frame for the specific type of vehicle you’re planning to build.

  • Planning to build a regular car or crossover? Go with the unibody. No other design combines reasonable cost, great strength, and lighter weight.
  • Going with a truck or an SUV for heavy loads and off-road adventures? Use a ladder frame.
  • Trying to go against Tesla in the EV market? Start with the skateboard chassis.
  • Building a race car? It’s either the space frame or the monocoque chassis.

Match the frame with the purpose of the vehicle, and you’re off to a great start!

 

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