Unibody vs. Body-On-Frame: What’s It Mean & What’s the Difference?
As car buyers begin to do their research while looking for their next car, they’re bound to come across innumerable car lingo terms. ABS, CVT, drivetrain, PHEV, torque, and RPM are just a few of these words on the long list. Two common car terms referring to a vehicle’s design are bound to pop up during your research: unibody and body-on-frame.
These two terms refer to the vehicle frame (also known as the chassis). They have a direct impact on the style of vehicles and their performance, particularly in SUV and truck segments. We’ll explain what each term means and how each type will impact your daily driving.
What is a Body-On-Frame Vehicle?
To start at the beginning, think of the frame as the spine of the vehicle. It’s the rigid base to which everything else is attached. It carries the engine and the drivetrain, for example. The earliest cars utilized a simple frame that resembled a horizontal ladder to which wheels were then attached. A large seating cabin, or body, then sits on top of the horizontal frame. At its most basic, this design idea still rings true today. Though, modern frames have obviously become more complex. Over time, as advancements in manufacturing have occurred, most passenger cars (and even many SUVs) have migrated away from this vehicle frame style. However, there are still numerous SUVs that retain a body-on-frame design. Additionally, nearly all of the trucks in the U.S. market are body-on-frame.
Advantages of Body-on-Frame
The reason that body-on-frame remains popular for trucks is due to some of the advantages of this chassis design. Body-on-frame vehicles tend to be taller and have higher ground clearance, offering true off-road capabilities. There is also greater flexibility across the vehicle. Think of an off-roading vehicle where the terrain is uneven. Individual tires may be at different heights compared to others because of rocks or mud. The vehicle is able to more easily flex and yield to these differing terrain heights. Ladder frames also allow for towing of heavier loads.
For car makers, body-on-frame vehicles are easier to redesign and modify. The same frame can be used over and over with changes made only to the body attached to it. This leads to lower design and manufacturing costs. Additionally, owners may find body-on-frame vehicles easier and cheaper to repair after accidents if the entire frame isn’t badly damaged.
Disadvantages of Body-on-Frame
At the same time, there are some distinct disadvantages to this frame style. Body-on-frame vehicles are often heavier and consume more fuel. Also, they score lower on crash test scores because they do not have distinct crumple zones. Furthermore, vehicle rollover is a particular problem since these vehicles have higher ground clearance and a higher center of gravity. This is especially true when it comes to cornering at high speeds.
What is a Unibody Vehicle?
Most passenger vehicles in the U.S. and even many SUVs have moved away from body-on-frame styles due to these disadvantages. Instead, automakers have shifted to unibody designs. Rather than an independent horizontal frame with a body attached on top, unibody designs feature a cage-like housing that merges the body and frame into a single piece. This is why crossover SUVs have boomed in recent years. They feature unibody designs while sitting at near SUV height levels in order to mitigate the disadvantages found in traditional body-on-frame SUVs.
Advantages of Unibody
Unibody vehicles have the advantage of being lighter than their body-on-frame counterparts. This translates to better fuel economy ratings. After the energy crises of the 1970s and 2000s and government-imposed fuel economy standards, automakers embraced unibody frames because of their fuel savings. Their lower center of gravity and more rigid frame also make them much less prone to vehicle rollover.
Unibody designs also score higher on crash safety test ratings. Not only are they more rigid, since they are comprised of a single unit, they also typically integrate a “crush zone” into their design. This allows for the vehicle frame to absorb the impact of a collision and even have designated space within which to crumple while simultaneously protecting the passenger cabin.
Disadvantages of Unibody
For automakers, creating a brand new vehicle calls for a complete redesign of the unibody frame. This may mean more expensive design and upfront manufacturing costs when transitioning from an older model to a newer one. Once manufacturing is up and running, however, they become cheaper to build due to a lower number of parts.
For consumers, this may also translate to higher repair costs in the event of a collision, particularly if the frame is damaged since it is a large and all-encompassing unit. That’s why you see many body-on-frame styles in industries that rely heavily on vehicles (think taxis, limos, and emergency vehicles). Since they are more rigid by design, unibody vehicles are also not the best choice when it comes to off-roading or towing large weights.
What Does This Mean for the Everyday Driver?
How does this impact your car buying process? If the first thing you’re drawn to is design, you may notice that most body-on-frame vehicles are boxy. Unibody designs are more dynamic. The Chevrolet Tahoe or Jeep Wrangler is the perfect example of this. These two body-on-frame vehicles have high ground clearance and large square builds with a wide stance. Contrast that with Chevy’s newly released unibody Blazer or the Jeep Compass. The Blazer has a narrower, more aggressive grille with sweeping sidelines and an upturned rear, compared to the straightforward Tahoe. In contrast to the Wrangler’s literal box proportions, the Compass has a more gently sloping windshield and downward raking roofline.
Unibody vehicles handle much more like sedans, which is why many buyers are flocking to crossover SUVs. Honda’s CR-V and Toyota’s RAV4 are the perfect examples of this. They have the space and sightlines of an SUV with the handling and fuel economy of a sedan thanks to their unibody designs. The Toyota Sequoia, on the other hand, has worse fuel economy and more body roll, though it also has more cargo space.
For buyers seeking a work truck, body-on-frame styles like the Chevrolet Silverado, Chevrolet Colorado, or the Ford F-150 perform the best. They have high towing capacities and are better at off-roading than their unibody competitors. Mid-size trucks like the Honda Ridgeline or the upcoming Hyundai Santa Cruz lean more toward daily city driving with occasional work capability. They have great fuel economy thanks to their unibody frames, but they are less utilitarian than their body-on-frame counterparts.