Most vehicles are built using either “body-on-frame” or “unibody” design. The terms refer to the style of the vehicle chassis (or frame).The chassis is like the skeleton of the vehicle. It supports the engine, drivetrain, suspension, and passenger compartment.
The Body-on-Frame Chassis
This design consists of 2 frame rails that run the length of the vehicle. They are joined together by several crossmembers. This type of chassis can also be called a “ladder frame.” The body of the vehicle is a separate piece (or pieces) that is bolted to the frame.
Body-on-Frame vehicles were the standard for many years. Today, medium and heavy-duty trucks, pickups, and some large SUVs still use this design.
The Unibody Chassis
In a unibody vehicle, the body and frame are considered one unit. The term is a shortened version of “unitized body.” It can also be called a “monocoque.” Most modern passenger vehicles are built using unibody construction.
Which one is better?
Each chassis style offers different pros and cons.
Body-on-Frame vehicles are heavier. So, they can haul and tow heavier loads. They also sit higher and allow for some flexing. This is good for ground clearance and off-road driving. However, the heavier vehicle is less fuel efficient. The high center of gravity can also make it more unstable.
Unibody vehicles can be made lighter. This makes them more fuel efficient. However, it also lowers their towing and hauling capacity. Unibody vehicles are also more rigid. They flex and twist less than a ladder frame vehicle. They also sit lower to the ground. This makes them more stable and improves their handling.