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The history of motorcycle frames

Sabyasachi Biswas | Updated on December 04, 2014

Space frame: The Ducati Monster has an easily identifieable trellis frame, in red

And why is a trellis frame better than most others?

A motorcycle is held together by what we call the frame, or the chassis. It is one of the most important parts of the motorcycle, yet it mostly remains hidden in plain sight. The motorcycle frame has come a long way from the early 1900s, when the first production machines came into existence, to this day. As with many components such as ABS, aerodynamic fairings and suspensions, the evolution of the frame can be credited to motorsports.

The simplest and the earliest frame that was (and still is!) used to hold a motorcycle together was the cycle frame. As the name suggests, it was a simple bicycle frame, with an engine strapped on to it. The construction is as simple as it gets – three critical points – the head stock or the T-stem, where the handlebar steering gets mounted, the crank-case was positioned where the pedals should have been, and the horizontal tube on which the seat and the tank rest.

But as engines started becoming heavier with the addition of evolving gearboxes and clutches, the bikes started suffering from excessive vibration and if the riders went too fast, the engines could even fall off! The points at which the tubes were welded together started showing cracks, results of stress from the vibration. Most of this was sorted in the post-WWII era, when manufacturers started using aluminium and steel alloys in the frame construction.

However, the key issue wasn’t resolved, and thanks to development in motorsports, manufacturers decided to bring in frames that were light and strong.

The development of the twin-downtube cradle frame fixed things up to an extent. In the twin-downtube, the engine is mounted on a platform between the cradle formed the said platform and the two tubes.

However, engineers looked up to the perimeter frame as the ultimate solution for more powerful and faster machines, as these frames had been in use since the 1920s in European racing motorcycles. A perimeter frame is simply the construction of two beams that wrap themselves around the engine, and join at the steering head and the swing-arm. This construction can be found on a lot of sports bikes.

The trellis frame is a further evolution of the perimeter frame – it uses the same philosophy of wrapping itself around the engine and joining at the steering head and the swing-arm in the least possible distance – except that instead of thick beams, the frame is constructed of welded members forming a lattice, or a trellis.

The advantages of using a steel or aluminium trellis frame are many. For example, the motorcycle can be made a lot lighter with this kind of frame as the trellis attaches the steering head and the swing-arm in the most direct possible way. Because the frame itself is like a lattice, it flexes a bit around fast corners, giving the rider a greater feedback. The trellis frame is also stronger and helps reduce the vibration from a powerful and high-revving motor.

However, a space frame is also a bit more expensive to produce than a cradle frame, as the engineering has to be very precise. Also, the quality of steel or aluminium is higher, thus increasing the production cost.

In India, we see the trellis frame on a few production bikes (the imported performance bikes have them anyway), such as the KTM RC and Duke motorbikes. However, the perimeter frame is extensively used in bikes such as the Honda CBR 150 and 250R (twin-spar frame), the Bajaj Pulsar 200NS and the Kawasaki Ninjas.

The others mass production motorcycles usually use a single or twin downtube cradle frames.

Published on December 04, 2014

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