Body-on-Frame vs. Unibody: Advantages and Disadvantages in Vehicle Design

Body-on-frame designs have almost completely disappeared from the automotive landscape, with only pickup trucks and large SUVs continuing to offer this particular chassis type. Their replacement — unibody — offers a completely different approach to building an automobile, and it has become the industry standard.

Why did the switch to unibody happen and why do trucks still keep one foot in the past? Let’s take a quick look at these two chassis designs and see what they have to offer.

Frame Basics

As the name suggests, a body-on-frame vehicle consists of two discrete components: a vehicle frame and an auto body, with the former sitting underneath the latter. The two parts are joined together on the assembly line but they remain separate from a design perspective.

The benefits of this approach were once plentiful, especially in the early days of the auto industry. By keeping the frame the same but changing the body design, automakers were able to update sheet metal and keep up with the torrid pace of style without having to make major engineering investments in the suspension or drivetrain of a vehicle. It also proved to be cheap to repair, since one could swap in new body parts or a new frame à la carte. Finally, ladder frame designs proved to be particularly resistant to twisting when subjected to high torque loads, which is precisely why they are still used on task-focused vehicles like trucks and large SUVs to this day.

Unibody Advantages

Unibody designs aren’t all that new, but it took quite a long time for the technology to become the industry’s go-to. Unibody vehicles combine the chassis, frame and body into a single unit, which brings with it several important advantages.

The first is weight savings: Since every part of the car is key to structural integrity, there’s no need for the added mass of a dedicated frame. Next, unibody designs make it much easier to protect passengers by directing crash energy away from the cabin. Finally, the absence of a separate frame frees designers in terms of styling and usage of space, allowing for more unique-looking automobiles and larger interiors and trunks.

Toughness vs. Versatility

Body-on-frame designs are still well-regarded in certain segments of the industry. The taxi and limousine business created enough demand to keep cars like the full-frame Ford Crown Victoria and its Lincoln Continental twin in business long past their retail expiry dates, as the vehicles proved to be tough, resilient and easy to repair. Off-roaders are also enamored with body-on-frame designs, although even all-terrain champions, like Jeep, have been building excellent unibody rigs for decades. In almost every other area, unibody vehicles are more versatile, less expensive to build and much lighter and safer than their predecessors.

For more information on body-on-frame vehicles, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Wikimedia Commons.