Have you heard the terms “unibody” and “body-on-frame” and wondered what they meant?
Think of it this way: Every human has a skeleton that acts as our body's central framework. The skeleton is to the human body as a frame is to a car.
From that analogy, it will be easier to understand that a car’s frame supports structure and works as points of attachment for vehicle parts.
Going back to unibody and body-on-frame, both words refer to the two primary types of vehicle frame construction methods.
Let’s take a closer look at both vehicle frame constructions — what they are and their advantages over the other.
Body-on-Frame & Unibody: Defined
Body on Frame
Have you ever seen one of those cheap toy cars that have (a) four tyres and a motor attached to a plastic base, and (b) an attractive covering—the car’s body—seating on top of that base?
Well, that design copies a real vehicle frame construction method. This construction method is called—body-on-frame.
As the name suggests, body-on-frame refers to a construction design in which the vehicle body is mounted onto an underlying frame (called the chassis). In other words, the automobile’s frame and body are two distinct pieces.
Unibody or Monocoque
In contrast, unibody (short for unitized or unit body) refers to a single body vehicle construction design. The body and the chassis are one, and the structural support and all other elements are merged into a single frame.
Unibody is also sometimes referred to as monocoque or unibody chassis.
For the longest time, body-on-frame was the only frame design that car manufacturers used, and you'll find it in many first-generation cars. Even today, many SUVs and trucks still use the body-on-frame.
However, nearly 100% of passenger cars have shifted from body-on-frame constructions to the unibody alternative.
Body-on-Frame vs Unibody: Which Is Better?
Let’s compare the features of each construction type and then determine which frame type is superior.
1. Repair Cost
The general argument is that repair costs are higher for unibody vehicles than for body-on-frame vehicles. The reason for that is obvious. When a unibody car is involved in a collision, the whole body absorbs the impact, which means you may often have to stretch out or replace the entire frame.
On the other hand, body-on-frame is made of separate parts, and consequently, it's easier to fix damaged components.
While the above argument has some merit, it’s also flawed. The extent of damage and overall repair cost will depend on the impact location and the strength of materials used.
So, yes, unibody repairs tend to cost more than body-on-frame repairs, but that’s not always the case.
2. Production Cost
Manufacturers often place different bodies on the same frame in body-on-frame vehicles. This allows them to save the money and time-cost of designing a unique structure for every new car.
Conversely, unibody vehicles are more expensive to manufacture since the body of every car model must be uniquely designed from the ground up.
3. Road Performance and Handling
Body-on-frame vehicles have a flat plane that can twist and bend, making them more flexible than unibodies. Consequently, they conform better to the irregularities of rough road surfaces and perform better on off-road tracks.
Meanwhile, some experts argue that the frame’s job isn’t to make a drive smooth. That’s the role of a vehicle’s suspension system. So, a ride in a unibody car should be just as smooth as in a body-on-frame vehicle, provided the suspension system is well designed and in perfect working condition.
4. Fuel Efficiency
The unibody takes the biscuit here. Unibody cars are usually more fuel-efficient than body-on-frame vehicles because they are generally more lightweight. By the way, less weight also implies better acceleration.
5. Hauling and Towing Ability
Body-on-frame vehicles are the favourites for towing because of their robust and heavy structures. The same result can be achieved with a unibody, however. The manufacturers simply need to make the unibody as heavy as the body-on-frame, which explains why we see more SUVs use the unibody frame.
Final Verdict: Unibody or Body-on-Frame?
The right vehicle depends on what you intend to use the car for. If you want a city cruise car with superb handling and grip on the road, then a unibody is your go-to vehicle. Body-on-frame, however, offers more stability on uneven paths.
FAQs about Unibody and Body-on-frame Vehicles
1. Is a unibody stronger than a body-on-frame?
Body-on-frame vehicles are usually stronger than unibodies. However, manufacturers can make a unibody car that’s just as strong and beefy by using a strong enough material.
2. What vehicles have a unibody?
Nearly all passenger vehicles use unibody construction — hatchbacks, sedans, minivans, crossovers, and some SUVs and trucks included. Some famous examples are the Honda Ridgeline, Ford Explorer, and Toyota Kluger (aka Highlander).
3. How do you know if your car is unibody or body-on-frame?
It’s difficult to tell by visual inspection which car has unibody or body-on-frame construction. In most cases, only a trained person who works with different cars can tell the difference just by looking at the vehicle. If you aren't an auto technician, the way to know which construction your vehicle uses is to ask an expert.
Would You Like to Learn More about Cars?
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By Damilare Olasinde