It was in the 19th century with the production of the Model T Ford that the ladder frame chassis was first introduced. It was such an inexpensive vehicle due to its low production costs that even the factory employees could afford to purchase one. The ladder frame design consists of a rigid framework and carries all the weight on its back, so to speak. From the beginning of vehicle production time, the ladder frame chassis was introduced due to its simplicity and robust design. Fast forward to modern-day SUV’s and most vehicle manufacturers have adopted the monocoque structure for most of their production line. So which option is superior and what are the pros and cons of ladder frame vs monocoque chassis SUV?
The Ladder frame chassis is a robust metal framework consisting of two large metal beams joined together by shorter support beams in between. With a Ladder frame chassis, the body and engine of the vehicle is mounted on top of the ladder frame making it a robust structure ideal for Commercial Trucks, SUV’s and 4×4 Utes that are meant to carry heavy loads for extended periods. With the Monocoque design, the chassis is forged into the basic structure of the vehicle creating one singular object known as a Uni-body, or Monocoque. Monocoque chassis is mainly used in the production of small SUV’s, luxury sedans, and hatchbacks, offering superior safety, ride dynamics and fuel economy due to its lighter framework.
If you would like to know the pros and cons of monocoque and when a ladder frame is a superior option, continue reading…
Monocoque chassis pros and cons
Monocoque design is when the frame is integrated into the body construction making it a single structure. The framework of a unibody is designed and built to support the weight of the vehicle. Manufacturers accomplish this by reinforcing the floor of the vehicle, reinforcing the B and C pillars and using bracing along with various parts of the body for overall strength and rigidity. The weight of the uni-body design is a lot lighter than ladder frame because it cuts out bulky steel rails as used in the ladder frame and this results in improved safety and fuel economy.
The unibody can be produced using a variety of materiel’s, depending on the intended function of the vehicle. Unibody Frames can be made from steel, mild steel, aluminum and aluminum alloy and even carbon fiber such as used in formula one racing cars. Other advantages are improved safety as the vehicles entire structure can absorb the forces of impact much better and manufactures can integrate crumple zones into the structure increasing vehicle safety. The handling is vastly improved since the vehicle is lower to the ground reducing the center of gravity and body roll associated with it.
The main advantage of the uni-body is its lightweight design since the metal framework extends to the furthest part of the vehicles body structure. This advantage negates the need to add more weight to specific vehicle parts to strengthen and reinforce it. This drastically reduces the vehicle mass and load it needs to haul which means manufacturers can add a smaller capacity engine to accomplish the same task a larger engine would in a ladder frame. This has a direct impact on the fuel efficiency of the vehicle.
Monocoque handling will always trump a ladder frame derivative when compared on-road. Ladder frame vehicles are not known for their fantastic on-road manners. This is due to the fact that the monocoque center of gravity is much lower which allows manufacturers to design more agile, aerodynamic vehicles resulting in superior performance on-road. Lower floor plan and ride height also mean easier exit and entry into the vehicle.
With the technology available today vehicle manufacturers spend millions of dollars on research and development thus producing smarter, lighter and safer monocoque designs. One of the primary focus areas are improved safety in vehicles and the monocoque offers exactly that. It allows for certain areas of the body to bend and crumble on the impact that it protects its occupants better. The vast framework also allows impacts to be absorbed better from various angles since vehicle accidents do not just occur from the front. This also vastly improves the safety aspect of the monocoque chassis.
Lower Production Costs
One ladder frame can be used on a variety of different body types. For example, manufacturers will release a ladder frame UTE like the Toyota Hilux then use the same ladder frame and put an SUV on top like the Fortuner. You can also have the same ladder frame but with different suspension setups such as leaf spring and dampers in the rear of the UTE truck and Spring and a damper setup in the rear of the SUV. Both on the same ladder-frame chassis with different suspensions for different applications.
Advantages of Unibody frame chassis vehicles
With the advancement in technology and software, the Unibody has become much easier to design, and modify.
- It offers better ride comfort and lower wind noise being lower and closer to the ground.
- Unibody gives you a more luxurious ride with tire and road noise being drowned out by advancement in build quality, sound deadening and the suspension setup afforded to the monocoque chassis.
- Less squeaky components make for fewer rattles and metal fatigue noises commonly associated with ladder frame chassis.
- The lighter body increases the lifespan of the tires, suspension, and other wear and tear suspension components.
- They also offer better balance in emergency braking and maneuvering situations.
Disadvantages of Unibody chassis vehicles
- More expensive to repair in the event of an accident due to advanced chassis technology, expensive components and the complete structure makes repairs more complex
- The Body on Frame construction has a very distinct advantage since it does not require the expensive process of laser welding
- Longer repair times needed due to the above-mentioned factors
- More susceptible to undercarriage damage being lower to the ground, like oil sumps and suspension components
- More prone to rust and moisture damage when exposed to water often with critical components being lower down and more susceptible to damage
- More expensive to develop and to do research and development on
Monocoque chassis have taken over the automotive industry by storm and have been the default option for all modern luxury vehicles. Monocoque chassis initially started its life in sedans and light hatchbacks but has transformed so much over the years with technological advancements and advanced software systems like Auto CAD that it is slowly beginning to infiltrate the large SUV market. Time will tell if the ladder frame chassis will ever become redundant but for now manufactures still opt for traditional Body on Frame or Ladder Frame construction for some of their vehicles.
Examples of Monocoque SUV’s
- Renault Duster
- Toyota Rav 4
- Ford EcoSport
- VW Tiguan
Unibody-Ladder Frame Hybrid
The Land Rover Discovery 3 & 4 SUV was developed with a Unibody structure on top of a ladder frame. Hence the excessive curb weight of 2.7 Tons in standard form. The latest version of the LR Discovery SUV has done away with the ladder frame in favor of the Unibody framework. We are not sure which direction Land Rover are going with their latest vehicles. Even the latest Defender which was a hard-core off-road icon has ditched the solid front and rear axles in favor of independent front and rear suspension setups. Monocoque chassis in an off-road vehicle was something that was scoffed at in the late ’90s when Mitsubishi released their Pajero’s NM SUV that way. Let’s wait and see, perhaps that day of a no-more ladder from chassis is closer than we think…
For now, let’s explore some of the advantages of the ladder frame in more detail
Advantages Of Body On Frame
Ladder frames suddenly seem archaic in comparison to monocoque structures now. Why would anyone still want to drive a ladder frame SUV in this day and age? Well it still holds the trump card in a few departments.
As mentioned before, the structure is extremely rigid and robust and is usually made to withstand various angles with weight being distributed unevenly for an extended period in off-road conditions. High torsional stress abilities make it far more durable than a Unibody structure since the framework carries all the weight and handles all the punishment off-road. Unibody chassis will require some serious engineering to be able to endure the amount of punishment a ladder frame can easily withstand. Manufacturers are, however, getting close, and we are already seeing large off-road luxury SUV’s being produced with Unibody chassis.
When conquering any off-road obstacle you will almost always opt for the ladder frame since he has such off-road prowess with its tough framework. They can literally take any terrain you can possibly throw at them. May that be rocks, gravel, sand, snow you name it, and while carrying a load. Here the ladder frame comes into its own. Ladder frames have a higher floor plan and raise the center of gravity due to its design. This allows the vehicle to boast higher ground clearance which is excellent for conquering off-road obstacles or handling any off-road challenges you throw at it.
The ladder frame chassis is the oldest design in the automotive industry. It has been phased out over the years in favor of the monocoque chassis due to safety, weight and ride dynamics advantages. A ladder frame is easier to work on to carry out damage repairs as it is a separate structure from the body. Many of the ladder frame components are isolated and makes repair work easier. You do not need sophisticated equipment to repair a body on frame chassis nor a highly-skilled mechanical engineer, just some basic knowledge and the right tools. This is a huge advantage if you ever get stranded in a remote location and only have the assistance of a bush mechanic to diagnose and repair the damage. Ladder frames afford you a higher towing capacity since the weight is connected directly or indirectly to the chassis.
A ladder frame can withstand high levels of stress under load and it takes a lot to bend or deform a body on frame chassis under load. It is the roust structure that has the ability to resist torsion and bending resistance. That is the amount of pressure or force required to bend or twist the chassis out of place. Due to the rigid structure and design of the ladder frame, it makes distorting or bending it virtually impossible during normal everyday applications. This is the main reason why body on frame chassis is chosen over monocoque to town heavy loads and by owners with SUV’s who want to tow boats, trailers, horseboxes, and caravans.
Disadvantages of Body on Frame
- Excessive weight is a huge disadvantage when it comes to vehicle performance and fuel efficiency.
- Heavier vehicle mass makes turning in emergency maneuvers difficult
- The ladder frame is much heavier than monocoque, thus increased fuel consumption and diminished performance.
- The high center of gravity is a negative when it comes to on-road manners, which is where vehicles spend most of their time anyway.
- The high center of gravity negatively impacts the vehicles cornering ability as there is excessive torsional flexing.
- Breaking is weak due to the vehicles size and weight
- Body roll can be reduced by upgrading the suspension to a stiffer setup, however, it will never be as crisp and direct as a monocoque chassis vehicle.
- Their lack of crumple-zones and safety features in older ladder-frame vehicles reduces occupants safety.
Examples of body on frame chassis vehicles
- Jeep Wrangler
- Land Rover Defender
- Toyota Land Cruisers
- Nissan Patrol
- Toyota Tacoma & Hilux
- Ford Ranger
- VW Amarok
Are Pickups with Ladder frames Safer than cars
The simple answer is, no. Not since the introduction of advanced software like Auto CAD, the safety advantages of a monocoque chassis vastly outweighs a ladder frame chassis. Manufacturers are able to keep the center of gravity lower with the monocoque structure thus decreasing the chances of vehicle roll-overs. Ladder frame Pickups have a high center of gravity, making them prone to roll-overs on impact.
Crumple zones are integrated into the framework of a monocoque chassis to make the frame bend and fold in a specific manner that deflects the impact away from the occupants, thus making the cabin safer. Ladder frames are robust and rigid and their whole purpose is NOT to bend and fold under pressure.
Ladder frame vehicles like modern pickup trucks such as the Ford Ranger, VW Amarok, and Nissan Navara have all incorporated safety features like airbags, advanced technology in the vehicles bonnet design to allow it to absorb impact better and ESP to name a few. These all improve the safety of a ladder frame pickup.
Certain parts of the monocoque structure can be reinforced to keep passengers safer. Rear and side structures of a monocoque can be specifically designed to maintain the structural integrity of the cabin in the event of a rear or side-impact, all designed to safeguard the occupants. The frame is also designed to absorb the impact a lot better. All these factors are reasons why a ladder frame chassis vehicle will never be as safe as a monocoque.
Honda Ridgeline (Unibody Pickup/Ute)
Just to confuse everyone even further, Honda has developed a pickup truck which has a unibody structure robust and rigid enough for heavy off-road work. The Ute has an AWD (All Wheel Drive) drive-train coupled with an independent suspension. (If you are interested in reading more about AWD vs 4WD, I wrote an article about that here) Honda has modified various parts to support heavier hauling, towing, and more aggressive off-road use. Apparently, sales were not that great for Honda, yet it was one of their most profitable vehicles.
Talk about thinking outside the box…. wow!
With all the evidence presented regarding the pros and cons of each chassis, I think it is safe to conclude there are no advantages and disadvantages per-say since both derivatives are built with two different applications in mind. Both are good in their own right. My personal feeling is that monocoque is ideal for city life where on-road safety and comfort is the main priority. Also, the Unibody offers superior fuel economy over the ladder frame so it is ideal for heavy stop-go city traffic. Ladder frame chassis is ideal for commercial operators, off-roading or a similar application. Settling this debate will ultimately boil down to the vehicle’s intended function.
Manufactures have to strike a balance between weight, cost and intended function when deciding which type of chassis to incorporate in a vehicle. Each chassis option will have its own benefits and disadvantages which in turn will determine the behavior and character of the vehicle.