Evolving from horse-drawn wagons, we have come so far in terms of chassis design in a car or a vehicle. Nowadays, cars are not only used as a mode of transportation but they are also used according to people's hobbies like road trips, rock crawling, track days, daily driving, and so on. Therefore, different cars are built with different chassis (frame) designs for various capabilities. A chassis or a frame is a supporting structure that acts as a skeleton of a vehicle. The most common chassis design in passenger vehicles is Unibody and Body-on-frame design. Each design has its own advantage and is used in different types of vehicles according to the need (off-roader and city car).
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A body-on-frame is a type of structural design vehicle that consists of a separate body attached to the rigid frame or chassis with powertrain, suspension, brakes, and other components by mounts. It was early of 20th century, virtually every car had a structural frame separate from its body. However, as time passed, most of the passenger vehicles have switched to unibody designs. But, there are some instances where body-on-frame vehicles are still preferred. All the heavy-duty trucks, and most of the pickup trucks and other off-road SUV segments where the toughness of body-on-frame is still ruling the industry. Cars like Toyota 4Runner, Toyota Land Cruiser, Ford F-150 (pickup truck), Jeep Wrangler, and the new Ford Bronco are some examples of current body-on-frame design.
Advantages
Despite its diminishing popularity, body-on-frame design possesses some benefits over unibody design.
Better Off-Road Capability: Because of the ruggedness of this design and other features like better ground clearance and driving dynamics, It can withstand twisting forces better when driving on rough terrain.
Easier to Design, Build and Repair: As it lacks the complexity combined body and frame, we can easily modify or replace the parts of the body or frame individually. It helps in reducing the cost of repairing the damage.
Better Hauling and Towing Capacity: Due to its sturdy structure and tolerance for torsional flexibility, this vehicle design can tow and carry more load.
Better Ground Clearance: As the body is on the top of the frame it has a higher elevation from the ground which protects body-on-frame vehicles somewhat better from the moisture of the road, which might otherwise lead to rust.
Easier to Design, Build and Repair: As it lacks the complexity combined body and frame, we can easily modify or replace the parts of the body or frame individually. It helps in reducing the cost of repairing the damage.
Better Hauling and Towing Capacity: Due to its sturdy structure and tolerance for torsional flexibility, this vehicle design can tow and carry more load.
Better Ground Clearance: As the body is on the top of the frame it has a higher elevation from the ground which protects body-on-frame vehicles somewhat better from the moisture of the road, which might otherwise lead to rust.
Disadvantages
Low Fuel Economy: The heavyweight of the vehicle with its high Center of gravity also reduces the on-road performance like fuel efficiency and dynamics of the vehicle.
Bad Handling: During cornering, the torsional flexibility of this design leads to more body roll which affects the handling characteristics of the vehicle.
Safety Issue: For better crashworthiness in a vehicle, there should be a crumple zone in a vehicle. And, because of its tough design nature, there is very less or no crumple zone in body-on-frame design, which makes it less safe in a collision.
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| Chassis Design (2017 Toyota Corolla) |
A Unibody is a type of structural design in a vehicle that consists of a single integrated body structure combining both bodies as well as a rigid frame or chassis with which other components(powertrain, suspension, brakes, steering system cooling system) are mounted. Vehicle structure has constantly shifted from the traditional body-on-frame architecture to the lighter and monocoque type body structure. Today, Almost all the passenger vehicles available in the market have unibody designs. Because of its unitized structure, this design is superior to the body-on-frame structure. Although SUVs are meant to be body-on-frame by their definition, almost all the SUVs produced these days are unibody designs. Cars like Toyota RAV4, Range Rover (present generation), Volvo XC60, and Honda Civic are some examples of the current unibody design.
Advantages
You might wonder why the vast majority of manufacturers are adopting the integrated body and frame design. And the reason behind that is that it possesses some benefits over body-on-frame design.
Better Rigidity and Handling: This design is less flexible with the twisting force (torsion). While going through the twisty roads a unibody vehicle has less body roll which results in better handling of the vehicle in corners.
Lighter Weight: As unibody cars don't rely on heavy steel rails like those of a body-on-frame vehicle, this construction cuts significant weight out of the cars reducing the material cost.
Better Aerodynamics: Due to the design nature of unibody cars, it has a lower center of gravity and less bulky design which makes them aerodynamically superior to body-on-frame design cars resulting in smoother ride quality.
Better Fuel Economy: Because of its lighter weight, handling characteristics, and better aerodynamics, the fuel consumption in unibody cars is significantly less.
Better Safety in Crash: Unibody cars are designed to prevent the damage that a passenger may experience during a crash, there are some parts or areas inside the chassis which can crumple to absorb the shock of collision which gives better safety to the passenger.
Lighter Weight: As unibody cars don't rely on heavy steel rails like those of a body-on-frame vehicle, this construction cuts significant weight out of the cars reducing the material cost.
Better Aerodynamics: Due to the design nature of unibody cars, it has a lower center of gravity and less bulky design which makes them aerodynamically superior to body-on-frame design cars resulting in smoother ride quality.
Better Fuel Economy: Because of its lighter weight, handling characteristics, and better aerodynamics, the fuel consumption in unibody cars is significantly less.
Better Safety in Crash: Unibody cars are designed to prevent the damage that a passenger may experience during a crash, there are some parts or areas inside the chassis which can crumple to absorb the shock of collision which gives better safety to the passenger.
Disadvantages
Less Off-road Capable: The cars with unibody design don't handle twisting forces as well as the cars with a body-on-frame design, which makes them less capable on bumpy roads.
Expensive Repairs: The integrated structure of the unibody design allows the whole body to absorb the stress produced during the crash this will increase the chance of unpredictive damage to the whole chassis which makes it hard to repair and increase the cost of repairing the car after any structural damage.
Less Hauling and Towing Capacity: The majority of modern SUVs and some pickup trucks segment(Like the new Ford Maverick and Hyundai Santa Cruz) is a unibody design. So, the pickup trucks and SUVs with the unibody design will have less towing and hauling capacity.
Expensive Repairs: The integrated structure of the unibody design allows the whole body to absorb the stress produced during the crash this will increase the chance of unpredictive damage to the whole chassis which makes it hard to repair and increase the cost of repairing the car after any structural damage.
Less Hauling and Towing Capacity: The majority of modern SUVs and some pickup trucks segment(Like the new Ford Maverick and Hyundai Santa Cruz) is a unibody design. So, the pickup trucks and SUVs with the unibody design will have less towing and hauling capacity.
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Automobile