Stupid is Still Stupid, Even When it's Old.

The Dpardo "Sickle" cranks -- a dumb idea rises again like
the killer in a bad slasher film.

Some bad ideas just keep coming back. I recently saw these "sickle power curved" cranks from Taiwan, although I understand they've actually been out for at least a year or so (where have I been?). The big claim is that they are supposed to eliminate the "dead spot" at the top (and bottom) of the crank rotation, and make it possible to turn a 58-tooth chainring with the same effort as a 50t ring. Yes, they come with a 58-tooth "monster" ring. According to the company's website, they sell for about $795.

Here is a claim from the website: "It is estimated that 25%-30% pedaling force will be saved, at the same time the saving power can put into the pedaling force. It can make the torque output increase immediately in opposition. So it can be thought and implement on logic." Okay -- that doesn't actually make sense, but it could just be a bad translation. The actual physics, however, are not subject to translation. They don't -- and can't -- actually work. The claims behind the design have been pretty well exploded time and time again, but every so often, someone digs it back up as though nobody's ever seen it before. The problem is, we have seen it before.

From the Z-torque Kickstarter campaign.
Spoiler alert: it failed.

A similar idea was put forth on Kickstarter recently, called the "Z-Torque" crank. It failed to meet its fundraising goal. Here are some claims from the Kickstarter campaign: The Z-Torque crank is "a patented design giving you the ability to generate more power over standard crank designs. This is achieved with the angled crank arm design which works on the simple principles of leverage and inertia." The creator goes on to say, "By repositioning the pedal in the manor (sic) in which we have, you now have a greater portion of the pedal rotation to generate power earlier and later than with a standard straight crank arm." I'm curious how they got a patent on something that's so clearly been done before.

The "evidence" presented in the Z-Torque fundraising campaign is obviously flawed. Note the side-by-side comparisons. The hand pushing straight downward on the vertical wrench vs. the angled wrench is supposed to correlate to the foot pushing downward on the top-dead-center position with the straight crank on the left vs. the "angled" Z-Torque crank on the right. It sounds good, except that the foot on the Z-Torque crank is still pushing straight down from the TDC position in relation to the spindle. The visual "angle" of the crank is not much more than an illusion.

From a PMP crank ad from the 1980s

Even the Z-Torque crank is just a re-hash of an earlier idea -- the PMP crank from the 1980s. The claims then were pretty much the same as the claims today. Here's an excerpt from the old PMP ads: "The unique form of the PMP pedal crank means improved distribution of the energy required in pedaling and a perfectly round stroke; the result: increased equilibrium." Funny thing about the PMP crank, though, is that the crank length was still measured as a straight line from the center of the spindle hole to the center of the pedal hole (the crank shown was very likely stamped 175 mm). If anyone sensed any more "power" using the PMP crank, it was probably due to the slightly increased leverage from a slightly longer crank than what they were used to -- 175 vs. 170 mm for example. Anything more than that was likely the power of suggestion (which is really powerful, come to think of it).

Funny thing about the PMP crank, though, is that it was hardly the first of its type, either. I was certain I'd seen older variations on the crooked crank idea, and it didn't take more than a few minutes of searching to find them. Lots of them, in fact. Here are a couple:

Here's one from 1931(from oldbike.eu)

A 1931 article about a crank that looks like it might be the same one shown above. Only the chainrings are different. (from oldbike.eu) The article states that the claims are based on a fallacy. "Another attempt to overcome the dead center bogy, and again not a new one, reaches us in the form of a pair of curved cranks of French origin and marketed in this country by Max Steiner."

As the article above stated, even the 1931 version was nothing new. This photo shows a crooked crank from 1897! (from retrobike.uk) The particular bend angle on this early version bears a strong resemblance to the one used recently on the Z-Torque.

The current Dpardo "sickle" crank probably won't be the last we see of this bad idea, but it's a sure bet that whoever markets the next one will proclaim it as a new "breakthrough." It won't be anything new. As is pretty clear, the idea is almost as old as the safety bicycle itself.