Evolution. The gradual change in expressed genes due to the inherent advantage conferred by those traits over competing traits. In the bike industry, it is the gradual change in the characteristics of technical systems due to advantages inherent in those systems as compared to other, competing systems. In biology, competitive advantage is mind bogglingly broad. It could be defined as faster, slower, shorter, stronger, lighter in color, etc. It's not even worth trying to sort it out without context.
In the bike industry, it's a little easier. I'd say the following are pretty generally accepted as competitive pressures:
- "Stiffness" which is really a measure of efficiency
So at some point in the past, the limitations of the cottered crank became apparent, and gave rise to the square taper BB system. The square taper BB was much better, but because competitive pressures are relative, it was only a matter of time before somebody developed something "better." In the case of bicycles, the pattern is to address the weakest link first, making it better, which exposes the next weakest link. Prior to the 80s, bikes were made of relatively narrow diameter steel tubing. Even the nicest frames would be considered "flexy" by today's standards, so the stiffness of the BB system was not the weakest link in the chain of performance, and since they were durable and inexpensive, they didn't get a lot of attention.
With the rise of alternative frame materials and larger diameter tubes, frames stopped being the most flexible (i.e. least efficient) component of the bicycle and other components started getting scrutinized, and at some point, some rider or manufacturer realized his (because during the time period in question, you can be sure it was a him) square taper BB was too flexible. A high school physics student knows that larger diameter tubes are stiffer, and since they are stiffer, can use less material, which if done properly, can actually make a stiffer component that is also lighter (a lesson Cannondale and Klein capitalized on with their oversized aluminum frames).
With frame stiffness increasing, all other components would be scrutinized, and the BB was a logical place to focus since it's amongst the first mechanisms transferring the force from the legs into forward motion. How do you make it stiffer? You take a cue from physics and use a spindle that's larger diameter. The first to try this was Magic Motorcycle Components with their crankset that was later licensed by Cannondale under their CODA brand name.
You want to talk about a design ahead of its time? Look into these cranks. I hesitate to bring them up because the design of these cranks jumps so many steps we need to examine. But hey, they were the first to try a larger diameter crank spindle.
In the interest of keeping these digestible, we'll leave it there for now. Do some digging on Magic Motorcycle and be prepared to be amazed. Next time we'll talk about Octalink and why Magic Motorcycle/CODA didn't succeed.