Tern Bicycles announces crankarm design contest

Tern Verge Duo with two-speed SRAM Automatix coaster-brake hub. Photo by Tern.

When I was born, bicycle frames were designed with paper and pencil and built using hacksaw, file and torch. There were (and are) a lot of great bicycle frames made that way. But computer-aided design (CAD) has changed the way most production frames are designed—just like it has everything else.

And CAD doesn’t stop with frame design; engineers use CAD for every part of the bicycle: including derailleurs, seat post binders and the subject of this post: crankarms.

To a non-engineer, a crankarm may seem like a pretty simple thing to design. It’s about as straight forward as it gets: a solid shape without any moving parts.

But a crankarm must withstand a lot of stress over time. A crank that breaks when the rider is pedaling out of the saddle can result in serious injuries. And it’s not a simple matter to remove weight, either. A poor design may remove too much material, leading to premature failure, or introduce stress risers that do the same thing.

If you have an established design but you want to make it lighter, there’s not a lot you can do—or perhaps more to the point, there’s a lot that you can do wrong.

So what happens if you let the rest of the world loose on the challenge?

That’s what Joakim Uimonen, Tern Bicycles’ Finland-based chief designer and enthusiastic 3D-model developer, is interested in finding out. Tern Bicycles and GrabCAD recently announced a crankarm weight-reduction contest, and they’re offering a Tern Verge Duo, valued at $999 US, as the first-place prize.

“Supra cranks have been in production for some time now,” Uimonen said. “And we have wondered could they be improved with relatively low effort. I designed the looks of the original crank set, but the weight and forging tool optimization was left to the crank manufacturer.

“This task is not the most challenging one, but making the winning solution is not that easy, either. Reducing material is easy. Analyzing the durability against strength requirements and creating optimal structure requires more skills. I am curious to see what kind of results such a contest will generate.”

So what’s GrabCAD? According to its website in mid-January, it’s a community of 77,208 CAD engineers and a library of 20,176 free CAD drawings. And it just scored another round of funding, worth $4 million, from the same group of investors that put $1 million into the organization in June 2011.

In other words, it’s yet another tech company with a devoted following and a business model that’s darn near opaque to me. But I digress. According to Josh Hon, vice president of Tern Bicycles, GrabCAD came knocking at his company’s door with the idea for a contest.

“I guess they found our bikes kind of cool looking,” Hon said. “We found the GrabCAD concept pretty interesting. In general, we believe that open systems foster a kind of creative chaos from which are born many interesting ideas.

“Our own development process is somewhat similar in that our product team is scattered around the world in Asia, the U.S. and Europe, and we have all different kinds of backgrounds. When we meet, there’s this kind of clash of ideas, out of which are many arguments and silly ideas, but also quite a few brilliant ones.”

So, are you feeling brilliant? Check out the rules here. And keep in mind the crankarm weight-reduction contest ends February 1, 2012.