What’s the Difference Between Unibody and Body-on-Frame?
- Body-on-Frame: The vehicle’s structure has two essential parts: the body and the frame. The body – the basic “skeleton” of the car that forms the cabin, engine bay, and cargo area – sits on top of a strong, flat frame, which supports the vehicle’s weight and holds the suspension and wheels. Think pickup trucks and huge SUVs.
- Unibody: The vehicle’s body also serves as the frame, supporting the vehicle’s weight and holding the suspension and wheels. Think of everything besides pickup trucks and huge SUVs.
Now, those worlds have merged: The Honda Ridgeline is a unibody pickup truck performing similarly to its body-on-frame rivals. It does, however, slip some when it comes to payload and towing capacity.
The Ridgeline won’t be alone for long: Hyundai has confirmed that it will launch its small unibody pickup shortly.
But that doesn’t mean body-on-frame vehicles are going away. The Jeep Gladiator pickup uses a body-on-frame approach, and other new entries are expected soon.
With these two approaches continuing to compete, let’s take a quick refresher course on the differences between the two.
This is the traditional method of assembling a car or truck. This process starts with an underlying frame, then the vehicle’s body sits atop that. The bed is mounted on the frame separately from the cab for body-on-frame pickups. Indeed, if you look closely at the side of a body-on-frame truck, you’ll see exactly where the cab ends, and the separate bed begins.
The frame generally features two long, high-strength steel rails connected by shorter cross-members. As a result, these are often called ladder-type frames.
That solid foundation remains essential for towing and hauling capability, and it’s better able to withstand extreme twisting forces. This is a significant advantage for off-roaders traveling over uneven terrain. On the road, however, body-on-frame vehicles are heavier, which means they get worse fuel economy. Also, the same rigidity that’s so helpful on a trail creates a noticeably harsher and less forgiving ride on the pavement.
In unibody construction, the body and frame are considered one unit. To be clear, that structure, sometimes called a monocoque, is composed of individual pieces. For the Cadillac CT6, as one example, 13 different materials have been welded, riveted, and screwed together to create its body structure, which also uses structural adhesive in some places.
A key benefit is that not all of those pieces have to be made of heavier metals such as steel. As automakers continue to reduce vehicle weight and improve efficiency and performance, they also introduce body structures made with lightweight materials like aluminum and carbon fiber. This doesn’t affect safety because unibody vehicles usually incorporate crush zones and other structures to keep crash forces away from occupants.
Along with their weight, fuel efficiency, safety, and performance advantages, unibody vehicles have gotten a big boost from the rise of computer-aided design and engineering. Before the unibody approach arrived, putting new bodies on top of pre-existing frames was a simple way to deliver a “new” vehicle. Today, though, technologies have made unibody design less complicated, reducing the need for as many expensive physical models before production begins.
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