The Skeleton Of A Motorcycle
Chassis or frame of motorcycle is that part which gives a basic structure of the motorcycle, just like the skeleton of our body gives us shape, strength and ability to do work, chassis is the skeleton of motorcycle. The chassis of a motorcycle is the part to which all the components like suspension, wheels, fuel tanks, seats, handlebars and many more are attached which in turn lends motorcycle its strength and ability.
Frame comes in a variety of shapes and materials which are based according to the cost and performance of the motorcycle. Lets discuss the varieties of frames, it’s use and what material it is made of according to its use.
· Single Cradle Frame
Take a look at your bicycle, the bicycle frame almost has a familiar look as a single cradle frame or single downtube frame. It is the most basic, common and cost efficient frame than the others. It is generally mated with steel tubes of various diameters which are welded together to form the frame structure. This frame consists of a single top tube and a down tube that starts from the steering head and runs underneath the engine to the swingarm pivot tube.
In this frame, the engine acts as the member of the chassis as a single tube supports the engine by passing under it. Though this frame provide stability to the motorcycle, but it cannot take the forces which are generated during heavy breaks. These frames are economical and is used in the motorcycles like Honda CG125.
· Double Cradle Frame
These frames aren’t much differ than the single cradle frame, a single cradle frame has one steel tube supporting the engine by passing down it. In double cradle frame or duplex frame, two tube supports the engine by passing down it.
In comparison to single cradle frame, this chassis stands ahead of it in terms of strength and rigidity and its cost isn’t too high than the single cradle frame. These frames are used in large quantity in India and are used in economical motorcycles. Double cradle frames are mated in the likes of Suzuki TS50ER motorcycle.
· Perimeter Frame
Also known as twin spar frame, it is the most commonly used frame in high performance motorcycles. Though the duplex frames have rigidity and strength, it wasn’t good enough for high performance and that leads to the invention of twin spar frame. This frame was designed in the process of improving the rigidity and handling of sports motorcycle. In this frame, the steering head is joined with the swingarm pivot in the shortest distance possible.
The beams joining the steering and swingarm pivot are stiff and lighter, and though it surrounds the engine, it doesn’t support the engine and thus the engine hangs with a number of supporting points. Initially these frames were made of steel but the modern twin spar frames are made of lightweight aluminum. This frame provides high rigidity at high speeds and during cornering. Yamaha’s delta box series are one of the most famous for twin spar frames in the world.
· Trellis Frames
Trellis frames and perimeter frames are the different interpretation of same idea of the frame design. Generally, it follows the basic concept of the perimeter frame as it also connects the steering head with the swing arm. It can be considered as the evolution of the perimeter frame. The only difference it holds is that two beams originate from the steering head all the way to the swingarm pivot.
Those extra tubes add solid rigidity to the frame. Generally, trellis frames are made of aluminum tubes welded together, therefore you can expect both rigidity and light weight from this fame. Moreover this frame doesn’t require heavy machinery for construction despite of its effective characteristics.
· Monocoque Frame
According to Wikipedia, it is a structural system in which loads are supported by an object’s external skin. If we follow this definition, then only the Vyrus motorcycles from Italy hugs this theory. Other manufacturers follow this in a different way where the engine is supported by the frame and acts as a part of it.
Motorcycles having extreme power demands high torsional rigidity along with light weight construction. These frames are single stiff piece of metal which require complex construction and high piece of precision and are made of materials like carbon-fibre and magnesium. These frames are required for hyper bikes and are really expensive compared to the other frames.