The Chassis Dilemma: Monocoque Or Body On Frame?
12th May 2018, Posted by : Elizabeth Mathew
For the past two years, India is witnessing some astonishing rise in the sales of SUVs. In line with the global trend, the demand for UVs is outstripping that for cars, and the last fiscal saw 9,21,780 SUVs going home to new buyers in India, up 20.97 percent. The increasing popularity of UVs is further reflected in the fact that in the financial year 2018, they accounted for 28 percent of total passenger vehicle sales, compared to the 25 percent in the year 2017. The legendary Bolero was Mahindra’s bestseller with sales of 85,368 units, up 23.13 percent, helped by the affordable sub-four-meter version. Mahindra’s focus on rural strategy has helped boost demand for models such as the Bolero and Scorpio in rural and semi-urban areas. Notably, the Bolero recently drove past the one-million sales milestone, 18 years after it first went on sale.
Now with increasing demand consumers are offered with a wide variety of SUVs plus not to forget the crossovers. While buying an SUV most consumers at some point of the time will come across the chassis type (one of the most important criteria). The two most popular types are the age-old body on frame and the not so old monocoque. Now, this article is not going to state which chassis is better. In fact, both chassis has its own advantages and disadvantages. Mahindra uses the body on frame chassis in most of the vehicles namely the Bolero and the Scorpio while the monocoque is implemented in the all-new XUV500 and in the upcoming micro SUV S101.
Body-On-Frame / Body-On-Chassis
In Body-on-frame, as the name suggests, a separate body is mounted on a relatively rigid frame that carries the engine and drivetrain. Hence it is made of two parts, the body and the chassis, the metal frame that carries the weight of the engine and body. It is a traditional and well-proven body style for an SUV. This is employed in most of the heavy-duty vehicles and off-roading vehicles because they are robust, can handle abuse and rough roads better. They are capable of taking in maximum load (“overload” friendly, I must say).
This design provides excellent stability and steadiness while off-roading. But dues to its heavier weight, the fuel efficiency decreases. The heaviness of the chassis also does not help in emergency manoeuvrings like sudden lane shifting or emergency braking at high speeds. So, unless you’re a serious off-roader or if you travel less in city traffic or looking for a vehicle which can take in heavy loads then, this is the type of chassis you need. From the manufacturer’s point of view, body on frame is less expensive to produce when compared with the monocoque and is mostly used in commercial and heavy-duty vehicles. All-time favorite Bolero and Scorpio uses the body on frame chassis.
The Monocoque is a structural system where loads are supported through an object’s external skin, similar to an eggshell. The word monocoque is a French term for “single shell” or “single hull”. A true monocoque carries both tensile and compressive forces within the skin and can be recognized by the absence of a load carrying internal frame. The monocoque is a modern and more scientific design. This makes it a single piece body which is more rigid. This design takes lots of R&D hence is costlier and relatively tough to make.
Monocoques by design are more stable, body roll is much lesser than the body on the frame since the entire chassis is a rigid, single unit. Because of its lightweight chassis, the fuel efficiency of the vehicle improves, plus the handling becomes smooth. Emergency manoeuvring becomes simpler dues to above-stated reason. But this is not used in any of the off-roading UVs just because it can’t handle much road abuse and will get damaged quickly if proper care is not taken. This kind of chassis will be liked by folks who live in urban areas. People who will have to go through all those hectic traffic sessions. The ride will be smooth and is considered much safer than the body on frame. The Monocoque is usually employed in everyday use and high-end luxury vehicles.
Ultimately the type of chassis required comes down to the requirement of the consumer. Both serve different purposes. One point which must be noted is that the body on frame construction is easier to repair. When off-roading, the damage might be done to either body or chassis or both. The body on frame construction has a very distinct advantage here as they won’t require a relatively expensive process of laser welding. Not all repair shops will have proper welding facilities which are required in case of damage to a monocoque construction. Also, the monocoque chassis are expensive to construct.
A body on frame construction will have an easier time getting repaired and reaching back to civilization as compared to monocoque SUV. The extra cost incurred during the production of monocoque results in its fine urban use and improved safety. Monocoque, body on frame or any type of chassis has to strike a balance between weight/materials used, intended function, vehicle design, and cost but the type of chassis used will have certain benefits and ultimately determine the function and character of the vehicle. The consumer must first realize his/her need and choose the apt chassis accordingly. The right selection of chassis will definitely help the consumer in the long run.