Chassis of motorbikes

In this post we will learn about the motorcycle framesMost of you would definitely be unaware of motorcycle frames. Frames or chassis are the most important structural elements of any vehicle. They bear the weight  and hold other parts in proper position. They  provide a definite structure to the vehicle and also help in dissipating the vibrations . Along with all these, they provide stiffness and structural rigidity to the vehicle and keep the wheels aligned.

Motorcycle chassis carrying engine

Material of frames

Frames are generally made from  steels as steels have sufficient  strength to bear the load and also they are tougher enough to bear dynamic loads. Generally tubular sections are used in construction of frame as they have very high stiffness. With technical advancement and increased requirement of lighter frames, new matterials like aluminium alloys, composites and carbon fibers are also being used. Aluminium is being used extensively in sports bikes as they have lower weight and fairly good strength. Some premium bike manufacturers are also using carbon fibers for this purpose. Carbon fibers are lighter and have extremely higher specific strength. They provide the much needed strength to the frame along with keeping its weight low. But their use is limited.

Understanding the structure of motorcycle frames.

The motorcycle frames have evolved from the cycle frames. In starting the motorcycles used bicycle like frames in which the engine was provided at the place of the paddle. Latter they evolved to more advanced and complex structures.

Labeled diagram of a motorcycle frame or chassis

Initially the frame and engines were considered  two different entities and engines were mounted on frames. The engines were like loads on frames but today there are many frame types which use the engines as a part of frame. The engines in these frames act as stress bearing components and are considered an integral part of frame. The frame connect the steering stem and the swing arm in such a way so as to support and hold other motorcycle parts. The steering stems are the parts which hold the handle bar and the front suspension. The steering stems are designed so as to keep proper caster angle. The rear part of frame is connected to the swing arm. The swing arms hold the rear wheel and the rear suspension. Many frames types use down tubes which are tubular section descending from the head stock or the steering stem.

Types of motorcycle frames

The motorcycle frames are classified in to many types depending upon their construction i.e.
1. Back bone frames
2. Diamond frames
3. Cradle frames
4. Perimeter frames.
5. Trellis frames.

Backbone frame

The simplest of all is the backbone frame. It do not have any down tube and the engine is bolted on the backbone. It is lighter and easy to manufacture.

Diamond frame

These frames are very similar to the backbone frames. They have a down tube attached to the backbone. The presence of down tube makes the attachment of engine guards easy. It also provide stiffness to the frame.

Cradle frames

These frames have a backbone and one or two downtubes. The down tubes and the backbone form a cradle in which the engine is mounted. They closely resemble bicycle frames. They are of two types-

1. Single cradle frame

They are the simplest and have only one down tube, which form cradle for engine

2. Double cradle frame

Chassis of motorbikes

They have evolved from the single cradle frames. They consist of two down tubes instead of one. They help in better mounting of engine and are more rigid and stiff as compared to the single cradle frames.

Perimeter frames

Perimeter frame

They consist if thin box like sections which wrap around the engine. They connect the steering stem and the swing arm through the shortest path. This increases the overall stiffness and rigidity  of frame. The engine in these frames are integral part of frame and act as a stress bearing component. You can see these frames in Apache 200r.

Trellis frames

Trellis frame

They are improved version of the perimeter frames. They consist of triangulated pipes instead of box sections. Triangulation increases the stiffness of the structure as the triangles are tougher to deform as compared to other polygons. These frames can be seen in KTM bikes.
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