Unibody vs. Body-On-Frame: What’s The Difference When It Comes To Autos?


in Auto FAQs and News
Black unibody frame

Unibody frame by J.Smith831 — CC-BY-SA-4.0

A search for a new car may uncover two unfamiliar terms about vehicle design: unibody and body-on-frame. What do these mean, and what’s the difference? Read on as we dive into the unibody vs. body-on-frame distinctions. 

Definitions—Unibody vs. Body-On-Frame

Unibody: Unibody construction is how most modern vehicles are manufactured, whereby the frame and body form a single unit. Hence, the unibody name, which is an abbreviation of unitized body or unit body.

Body-on Frame: As the name implies, body-on-frame manufacturing is when the vehicle’s body is mounted onto the frame. Think of the frame as the car’s skeleton; it’s a typical design among larger pickups and SUVs.

Is one vehicle build type better than another? Each construction method has its pros and cons, but it depends on your vehicle requirements. If driving involves towing a large boat or heavy trailer, then a body-on-frame truck or SUV is the obvious choice. On the other hand, a preference for better fuel economy and smoother handling will steer you towards a unibody vehicle. Keep reading as we break down more details.

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What to Know about Unibody Vehicles

The earliest unibody cars date back a century, with Italian brand Lancia filing a patent in 1918 for the innovation. The first American unibody cars appeared in the 1930s, but the style wouldn’t gain popularity in the U.S. until the 1960s as manufacturers sought ways to reduce weight and improve safety. 

But the average consumer doesn’t think about how cars are built. In the case of unibody construction, the chassis structure, floorboards, and body are all formed as one unit. Manufacturers prefer this approach because of better fuel economy and crash safety. Car buyers also tend to prefer a smooth-riding vehicle (no matter the size) with car-like handling, a unibody trait. 

Unibody Advantages

Unibody construction offers compelling advantages for car companies and consumers:

Easier Design and Manufacture: Because a unibody vehicle is engineered and built as an integrated unit, automakers spend less time developing each model. Sophisticated computer systems and advanced robotics enable brands to bring a completely new car from concept to the street in as little as 36 months, which used to be five to eight years. 

Improved Fuel Economy: Unibody construction enables carmakers to build lighter vehicles that use less fuel than a comparable body-on-frame automobile. 

Enhanced Safety: Unibody design provides inherent safety advantages over body-on-frame construction. To begin with, a unibody vehicle has a lower center of gravity, making it less likely to cause a rollover. In addition, crumple zones are engineered into unibody architecture for better crash impact absorption. Interestingly, the Insurance Institute for Highway Safety did safety testing of the body-on-frame 1959 Chevrolet Bel Air and the unibody 2009 Chevrolet Malibu. Despite the Malibu’s smaller size, its crash test results far bettered the Bel Air.

Upgraded Ride Quality: Engineers can better accommodate pavement imperfections with a unibody design. So, things like highway expansion strips are far less noticeable during driving. Unibody architecture also allows for more refined handling, especially on curves and corners. 

Greater Availability: There are simply more unibody vehicles on the road, so finding one is easy.

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Unibody Disadvantages

But the unibody design isn’t perfect. So consider these cons if you’re shopping for a car with a unibody structure.

Limited Towing and Hauling: One of the most significant drawbacks to a unibody car is that it can’t tow and carry as much as a body-on-frame vehicle. For example, a Ford Explorer can tow up to 5,600 pounds, while a Chevrolet Suburban can handle a trailer up to 7,800 pounds. Body-on-frame pickups have even greater capacities.

Restricted Off-Road Capability: A gravel or smooth dirt road is no problem for most unibody vehicles, but things get trickier with more challenging surfaces. Extreme trails with boulders and deep ruts are best handled by body-on-frame vehicles like the Jeep Wrangler and Ford Bronco.

Greater Expense: The sophisticated nature of a unibody system comes with higher development and production costs for the manufacturer, so this gets passed along to the consumer.

Increased Repair Costs: Collision repairs for a unibody vehicle are more costly due to how integrated the body and frame are. In other words, the body shop has to spend more time fixing things after an accident.

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What to Know about Body-on Frame Vehicles

The earliest automobiles had body-on-frame configurations. It’s a straightforward design where the separate body structure is mounted to an independent frame with a powertrain. While the body-on-frame arrangement is no longer the dominant method for building cars, it serves a purpose for larger vehicles with more extensive hauling and towing capabilities. The body-on-frame design mostly underpins today’s larger SUVs and pickups and heavy-duty commercial trucks. 

Body-on-Frame Advantages

Body-on-frame vehicles are still around for a reason; here are some of the most common considerations.

Enhanced Off-Road Suitability: Uneven travel surfaces like trails create twisting forces best handled by a body-on-frame vehicle. These trucks and SUVs also sit higher up, making for better ground clearance (a helpful feature when off-road or dealing with snow or mud).

Higher Towing and Hauling Limits: Pulling a trailer or loading up a vehicle adds stress to its very structure. Thanks to a separate frame, a body-on-frame vehicle can handle these duties with ease. For instance, the RAM 3500 heavy-duty pickup can tow as much as 37,090 pounds.

Reduced Repair Costs: Accident repairs for a body-on-frame vehicle tend to be less expensive because components are easy to replace and work on. 

Improved Moisture Protection: A higher ground clearance means less exposure to surface moisture (rain and snow) and road salts. This same height allows for easy cleaning and inspection underneath. 

Body-on-Frame Disadvantages

There are trade-offs to consider with a body-on-frame vehicle.

Greater Weight: More weight translates into less-precise handling and more frequent tire replacements.

Lower Fuel Economy: The extra bulk of a body-on-frame vehicle also means more trips to the gas station.

Less Sophisticated Crash Protection: Body-on-frame trucks and SUVs lack energy-absorbing crumple zones, so accidents can be more severe for occupants and other vehicles.

Less-Smooth Suspension: Even luxury body-on-frame SUVs like the Cadillac Escalade and Lincoln Navigator have truck-like ride characteristics.

Popular Body-on-Frame Vehicles

  • Chevrolet Silverado 1500
  • Ford F-150
  • Nissan Frontier
  • RAM 1500
  • Toyota Tacoma

Unibody vs. Body-On-Frame: Which One to Buy?

There’s no right or wrong answer when it comes to the unibody vs. body-on-frame debate—the best way to choose is to prioritize your most important requirements. Consider a unibody vehicle if your needs lean towards a fuel-friendly, comfortable ride. On the other hand, a body-on-frame SUV or truck has people and cargo hauling and towing capabilities like nothing else on the road.

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