But you have to input ALL that energy into the spring in the first place by loading the pedals to deflect the crank spring. You don’t get any free energy in this system.
It’s not like running where normally some energy would be dissipated (lost) into the ground whenever your foot lands, but could be partially recovered by using a sprung shoe. In the case of a bicycle crank all your energy goes directly into turning the crank.
Oh I know…
I was just stating they are going into the bandwagon of “energy return” from running and trying to do it in cycling…
but as you and other have stated, there is no free energy…
kind of ironic… This “energy return” in cycling have similar problems as “power” in running.
You THINK it can be done. But we all know it not possible,.
Some energy probably gets wasted, mostly because of poor coordination or body mechanics. Eg, the upstroke leg still pushing down etc. Similarly, there might be force components into the frame or somewhere where they don’t contribute to moving the cranks. But I don’t think these cranks would be able to help with any of that.
Oh for sure there is wasted energy upstream. But not from the perspective of the load that finally gets applied to the pedals and hence crank torque and power. That’s why it is very dubious to be claiming that you need less power measured at the crank for a given road speed. They might measure less load on the pedals, but that’s just a quirk of how you are measuring it rather than a reduction in crank power.
A crank is about as pure a lever as you can imagine. So Torque = Pedal Force x Crank Length and Power = Torque x Cadence. There is no place in this line of physics for adding a spring rate to the crank to magically increase power by 4% or whatever. The only variables that are going to affect power output at the crank are pedal force, crank length and cadence.
If the demonstration of the effects was based upon measuring a higher power output at the pedals for the same physiological effort level, it would have more chances of flying as an argument. But to argue that less power at the pedals is needed to deliver the same power to the hub is physically absurd.
Since when this has been an impediment on broken promises?
cough iq^2 cough
It actually concludes there is no difference in measured VO2 vs hub power between the fixed-crank and the elastomer version. The only difference is (at a given VO2) a lower power measured at the pedals. I don’t know who wrote the conclusion of the article, but I sure expect he got at least a nice bottle of wine in compensation.
If they were arguing less drive train losses, for example less chain friction, revolutionary chain and teeth shape, etc, more power at the hub would be possible. Maybe even less chainset flex. But that’s not what they say.
Mm, I think that equation is only valid for cranks of infinite stiffness.
Yeah I noticed that too. Same input effort, same output power at the hub. Dodgy power measurement at the pedals would be my conclusion.
For when the interest in magic springs wears out, y’all can head over and enjoy the fantastical powers of the letters Z and L.
Not really, it should hold for any crank that doesn’t snap off during operation. All the increased flex affects is the timing of the load transfer.
I had to quit following Road.cc because they insist on posting those articles with regularity. Funny once, not funny every month. 
LOL - I just did a quick search for PMP cranks and they had the article with others too.
Anyway, I want a free pass because I remember seeing pictures of Ian Cammish riding PMP cranks in the 80s. In British cycling magazines. And thinking with my high school physics knowledge - “That makes no sense at all”.
But importantly, since I am an American who was living in a small New England town at the time, getting hold of a British cycling magazine was quite the feat and that gives me serious inter web credentials 40 years later (more LOLs)
Hilarious! It’s amazing what junk appears on the market from time to time.
No question, totally worthwhile to post here (I even considered pulling those very examples 
) because they are quite relevant to the “reinventing the wheel” that these guys seem to be claiming. I haven’t dug in, but based on the comments here and my prior consideration on the topic, this new version is interesting, but more of the same snake oil.
I’ve got an idea. How about telescopic crank arms that extend on the downstroke to give more leverage and then retract on the upstroke to make it easier to push over the top of the upstroke. They could be motorised and programmed electronically for a “custom” pedal stroke profile.
…or you could change the shape of the chainring…
You joke, but that and other ideas have been patented and/or built…