Rational Bicycle Frame Design : Giving Consideration To Functionality

Courtesy : AluMatter

A lot of people these days question the age-old triangulated design of the bicycle frame. They think bicycle design is "dead" just because nothing has changed for a close to a century in relation to this structure, the biggest element that stands out when any observer sees a bicycle. And designers around the world are increasingly trying to break free from this constraint and come up with the most bold, radical designs. Some are successful for a while, others are hype that never deliver. Yet, the classic structure has endured through all the competition.

But its nice to ask why, or how this simple design has stuck with us for more than a century. 1887 to 2008 is 121 years!

See, there's a sound engineering principle behind it. Let me explain.

A structural member is weakest when it supports a load which tends to bend it. We all know that. If this member is propped up from below, the load is carried in compression, and much more load can be carried. Still better yet is an arrangement that is strengthened by a cable such that it is in tension when applied with a load. This is the triangulated structure and it is the lightest and strongest structure arranged in such a way that its members are all in tension or compression, but never in bending.


I'm not a historian but I reckon that this brilliant idea might have made its way from age-old bridge and roof design somehow into bicycles. And people soon found out how they could have the lightest structure possible, which is strong at the same time to resist the forces encountered on riding.

Most, if not all, bikes we see these days are derivatives in some fashion or the other of this classic frame structure. The bike may have a few bends and curves here and there, but the fundamental principle still stands. To get a perspective on the road bike business, it is partly around these minimal changes that bicycle companies try to make money off you.

So, if anyone can come up with an alternative frame design that does the job better, without diluting the advantages of the original truss frame, we'll see something new. Until then, keep crying...and pass the hanky. (Note that some folks tried to extrapolate the triangulation to the fork as in the Pederson Bicycle... see below. Yet, interest in these bicycles also diluted with time)

I had to revive a nice snippet of text from David Gordon Wilson's classic "Bicycle Science" (MIT) to share a few other ideas on frame design.

In it, the author talks about the basic premise behind a diamond truss frame that we all commonly ride around, its drawbacks (which we can witness through all the pictures of broken steerer tubes & forks) , and what generally is expected out of a sensible bicycle frame structure. In the following short sections, he quantifies some of the peak forces experienced by the frame at various points, and gives tips on how to set up instrumentation to measure these stresses, both for folks with the equipment to do it and for those who don't have the money.

To put a bottom line to this post. there may be many fancy conceptual ideas floating around on the internet out there that make headlines and often bring much excitement. But if the resulting machine cannot ride properly or snaps under the application of forces, its not only useless but also dangerous for human use. In this regard, it violates the basic canon of engineering ethics which states something like : "Engineers shall hold paramount the safety, health and welfare of the public and shall strive to comply with the principles of sustainable development in the performance of their professional duties."

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Reference Image Of The Pedersen Bike (Visit Pederson Bikes for design features)

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Additional Resources For Reading :

1. Bike Think : Frame Flex And Strain Energy
2. AluMatter : Bicycle Frame Design Requirements