Looks like a new version of the rotor crank I used in the early 2000s
So they engineered the crank arm to be more of a spring than it already is. This is one of those “so obvious why didn’t I think of it first” things.
Wouldn’t any energy saved in the the “dead spot” be lost in the energy needed to recompress the spring?
I tend to look at these things with the sceptical eye of “the big companies would already be doing this if it was a thing…”
With much side-eye.
Put me in the “very sceptical” bucket.
I’m pretty skeptical as well…but there are plenty of examples of small, innovative companies beating the big boys to the punch…disc brakes, suspension forks, clipless pedals, aerobars, etc.
ETA - I probably need to dig deeper into the mechanics of the cranks, but something that immediately jumps out at me is the Newton’s law of conservation of energy - it can neither be created or destroyed. So the energy needed to load the springs would be returned at a lower rate…so where would the increased efficiency come from? You still need to load the springs and wouldn’t that require more energy than a standard crank? (Author’s note - I suck at physics and failed it in both high school and college, sooooo…)
I obviously can’t speak to their thinking, but my guess would be something like this: you ‘take’ a little energy from the most powerful part of the pedal stroke and ‘move’ it to the least powerful/ dead spot. Even if the energy returned is less than you put in (which it obviously is), the result may still be a more efficient stroke overall because of where the power was applied.
“We see this as similar to oval chainrings which, as far as I know, were not a problem for the UCI.”
Except oval chainrings don’t do anything.
Yup…totally on board with that as the concept. But wouldn’t you still need to apply more force than with a traditional crank so that you could “load” the carbon spring? IOW, the force needed applied to a traditional crank is x while the force need to load these cranks would be x + y?
I guess if the returned energy significantly outweighs the inherent nefficiency of the “dead spot”?
Like i said, I suck at physics…I’ll defer to the smarter amongst us.
This would likely be it.
Remember, at one side’s dead spot is near the other side’s peak torque production.
I can’t work out how to read the full journal article they link to on their website but from just skimming though it seems like all they prove is that powertap pedals read lower power when they are fitted to these springy cranks
It probably depends how the Powertap measures torque and calculates power.
power (watts or horsepower) = torque (lbft or Nm) x rpm (cadence) / constant. The spring will eat up some force as it flexes and potentially release a negative torque in the dead zone.
Favero make a big deal about being the only pedals that cope with oval chainrings.
but I might be doing them a disservice - I don’t think I fully understand the protocol or conclusion
CONCLUSION: Lower power, but similar VO2 during EXP compared to CON supports the notion that the IMPACT crank improves effective power during cycling. Although small in magnitude, the effect was large and could be of interest to competitive cyclists or triathletes.
EXP was spring and CON was no spring - so lower power with spring for a given VO2… isn’t that bad?
I’d like to read the full paper.
You’re only going to get out what you put in, so no nett gain. Difference with the running shoe is that you have gravity assisting to compress the shoe to create the spring. Not the case with the crankset
Exactly where my mind is…
I’ll wait for the skin suit that captures some of the 80% or whatever of my energy that goes to heat production and converts to useful kinetic energy cause that loss just burns me up. Or the compression seatpost / handlebar / frame component that converts every bump I hit to usable energy or maybe I’ll just buy an ebike if I want some assist.
Add some solar panels to the skin suit while we’re at it.
It seems like it’d be increasing the velocity of the pedal at TDC/BDC so that it gets back to the power phase of one of the legs sooner. That seems like it’d (maybe) increase power but not efficiency; as you’ve noted it’s taking energy to load the pedal in the first place.
It’s been a while since I’ve taken material science but having a spring load and unload 90-180 times per minute for hours on end seems like it’d be an fatigue issue.
“The tests showed that with conventional cranks an average of 197.2 watts was required to hold an average speed of 19.3km/h at a cadence of 71rpm for 30mins on a Tacx Neo trainer set at a 3% slope. The use of an Impact chainset is said to have reduced the power required to an average of 187.8 watts”.
they should’ve done a forum search:
“Taxc Neo and power meter discrepancies”.
Where did you find that text? How did they measure the power?