Tuesday, October 11, 2016

Crazy Cranks

What could be simpler than a bicycle crank? It's hard to imagine a simpler, more efficient mechanism for transferring leg motion into circular motion into forward motion. But almost since the beginning of bicycles, people have been convinced there's a better way to propel a bicycle. Riders can only apply power on the downstroke, and some see that as a waste of energy. Since the earliest days of the bicycle, tinkerers and inventors have come up with all kinds of ideas to increase power, minimize effort, and eliminate "dead spots" in pedaling motion - some that defy logic and physics, others that are bizarrely complex.

Remember these?

Dpardo "sickle" cranks: a fairly recent reboot of an old, thoroughly de-bunked concept . . . 
. . . previously seen in the '80s as the PMP crank, which itself was just a rehash of cranks that were hailed as "revolutionary" in the 1930s, and in the 1890s before that. Every generation or so, these things come back, reintroduced by people who are thoroughly convinced they're something never seen before.
Lever-drive, or treadle-drives have been tried again and again - like this Alenax in the 1980s. Another idea that actually dates back to before the safety bicycle.

Oval or elliptical chainrings are another questionable attempt to get "free" power and eliminate "dead spots" in the pedaling motion. Some people swear by them, but actual scientific evidence of their effectiveness is lacking. And again, they're nothing new . . .

. . . The Durham elliptical sprocket made similar promises - but also made front shifting impossible. And like other "innovations," they were actually an old idea by the 1970s.

One recent company took the route of altering the pedals instead of the crank itself. The CrankTip pedals move in an elliptical path as a rider turns the cranks, supposedly giving a variable effective crank length - and increasing torque on the downstroke.

Now there's another entry in the crazy cranks lineup that might actually be something no one has ever seen before - the Cyfly drive system. This thing is probably hands-down the most complex crank unit I've seen. Combining a special gearbox, a pair of multi-link crank arms, and an elliptical (almost rectangular) chainring, the Cyfly mechanism causes the crank arm length to change dramatically throughout the pedaling motion. The company boasts 33% more torque at the same pedaling effort.

The Cyfly crank was introduced at this year's Eurobike, in conjunction with the German bicycle brand, Moeve. The crankarms change in length by about 20mm throughout their stroke.

As the pedals turn, those multi-linked crankarms chug back and forth, constantly changing --lengthening and shortening, and supposedly increasing torque during the "power stroke."

If you're thinking that such an unusual new crank design would be interesting to try, allow me to mention that the Cyfly is not something a person can just install onto their existing bike. The system's oversized gearbox, which is needed to keep the crankarms chugging in proper synchronization, requires a specially-built frame.

One thing that doesn't get mentioned anywhere is the width of such an unusual crank. There are no measurements given anywhere, but just from the look of it, with its extra linkages and everything, I'd say it's a safe bet that this thing would make a person pedal like a duck - putting the "Quack" in "Q-factor."

The system also adds a good bit of weight, too. The version shown above is listed at about 2kg (a little over 4 lbs!). I guess that's a big improvement over the earlier prototypes, though, because I read in BikeRumor that the first version weighed nearly 15 pounds!

Evolution of the idea. Looking at that first one, it's no surprise the thing weighed 15 lbs.
I know that there are lots of claims about the advantages of such a crank, but as usual, I'm skeptical. Whether it actually works as claimed or not, I wonder if the difference is worth all the added complexity -- something this crazy crank has in spades.


  1. More moving parts = more points of failure, no thank you. And if it needs a proprietary bottom bracket, then I can't even imagine a scenario where this thing will ever see a real sale.

    Also, I wonder what all that weird movement does to a rider's knees after a while?


  2. Was waiting for you to mention Power Cranks.

    Decoupled from one another, you pedal each crank at it's own pace, the idea being to train your legs independently I guess. By far the most confounding, annoying cranks I ever had the *pleasure* of trying on a customers bike.

    They came off a few short months later, too.....

  3. Just for fun some time you should create a "kangaroo bike" by putting your two cranks in line. There's no bio-mechanical advantage to the loping cadence that's created. However your wife and kids will be splitting their sides laughing at you and you get a few double takes from the neighbors. When it's not fun fun any more you can turn one crankarm around 180 degrees and all is right with the world again, unlike some of these other "innovations".

    1. I have lready done it. It was funny...until i fell. :D

  4. Favorite shop stunt on the new guy was to use an old pump and fill their tubes with water, while (during square taper days) repositioning one arm by a 1/4, so you have 90 degrees instead of 180.

    They immediately notice the one (amid much hilarity) but the water is more subtle, and a serious head scratcher for some, heh, heh, heh.... =:D

  5. In principle, the Ercih Split cranks were the same sh*t like CyFly IMHO: http://www.sonic.net/~ckelly/Seekay/splitcrank01.jpg