Sounds like neither of you actually “read the article”:
Some of that spring-back energy probably helps turn the drivetrain while some of it may behave in a negative manner. However, there’s a fair amount of debate about how much energy is returned. The answer to the energy-return question involves kinematic analysis far outside the scope of this article. For now, we’ll assume that all of those 4.8 Watts spring back in a way that doesn’t help turn the drivetrain nor hinder it. As mentioned before, the most flexible crank in this review shows about 50% more deflection than the stiffest crank. Our FEA crank is quite flexible, and it absorbs 4.8 Watts of a 300-watt effort. Strain energy, roughly speaking, is inversely proportional to stiffness. We can use these relationships to calculate that at 300 Watts, our flexible crank absorbs 4.8 Watts, or 1.6% of total power output. Meanwhile, a 50% stiffer crank absorbs 3.2 Watts, or 1.07%, in strain energy (technically, strain power). That’s a difference of 1.6 Watts (or 4.7 watts at our tested 880 Watts).
Remember, this assumes that no strain energy is returned to the drivetrain. That’s not to say that crank stiffness is irrelevant, there is a measurable difference. It also provides all the psychological and “feel” benefits described at the beginning of this section. A stiff crank also incrementally improves efficiency by keeping bearings aligned, keeping the pedals more directly beneath your feet, etc. Keep in mind that this 1.6% calculated strain energy absorption represents an upper bound of energy dissipation—that is, the maximum possible energy loss due to crank flexure. Real cranks are much stiffer than our modeled crank and therefore store less strain energy. Moreover, a great deal of that stored strain energy is likely returned to the drivetrain. The real-world losses to crank flexure are, in all likelihood, a fraction of that number.
It seems like there’s a certain degree of guesswork and ignoring the first law of thermodynamics working together in this argument.
I would like to see some measurement of that alleged spring effect happening from tip of crankarm towards axle, back to the other crankarm or whatever the suggestion is.
Elastic deformation, i.e. flex, does not equate to lost efficiency unless the system absorbs the energy. Spring-like mechanisms absorb energy at wildly different rates. On one end of the spectrum, you have something like a coil spring made of steel, which absorbs almost no energy. On the other end, you have something like rubber or a urethane elastomer that absorbs a lot of energy.
Do I get some “successful thread derailment” badge for bringing up the flexiness of Red cranks? My bad. I’ll say I have some eeWings cranks on my MTB and they are SUPER nice, albeit also SUPER expensive.
Back to the point, the new group looks very promising in terms of ergonomics, which is the main thing I care about. I’m sure it’ll be very light, but Force—>Red is usually not worth the $$/grams to upgrade for me. (And yet I have eeWings for some reason?) And wireless electronic shifting has taken any “superior shifting feel” argument out of the equation.
I hope it’s compatible with Force calipers and hoses, as the only upgrade I’d be likely to make would be the brifters, i.e. the ergo parts.
Elastic deformation and springs, by default, involve energy loss per cycle, that’s what is defined by the Q factor. Not sure if you are trying to argue the opposite by mentioning things that (of course) confirm what I said: energy lost in the system isn’t recovered by the system. I.e., the first law of thermodynamics.
But to the initial point, I’m open to being shown that the energy lost to deflection of a crankarm is indeed recovered elsewhere in the system instead of being “lost”. I don’t see how and where that could happen by I’m sure I’m missing something.
A pretty decent measure of crank loss/performance would be running powermeter pedals along with a hub-based powermeter. Swap out the crank (everything else being the same) and that should give some indication of crank performance differences (ie - compare relationship between pedal and hub power). Would not be a perfect test and would likely differ by individual, but should be able to highlight any measurable performance differences between cranks (but wouldn’t really tell you if it’s due to stiffness or other factors)
I apologize for contributing to the thread derail.
Back on topic, I saw something on weightweenies indicating that a 1x13 sram red groupset may be part of the upcoming plan? Not sure on sourcing of the info, but sounds intriguing since 13 speed cassette spacing seems pretty sensitive, and having the mech be electronic would help avoid the inevitable tuning needed as cable shifting ages etc
spitballing a bit more here, perhaps the 1x13 electronic would be UDH only.
Getting the advantage of more consistent alignment due to elimination of hanger, and also more likely to pick up spec since 1x13 range seems particularly attractive for gravel frame marketing and riding.
no idea on watts due to shape/size change of hoods.
big potential benefit for me though would be ability to put down power fully while shifting though. not a necessity of course since shim 12s shifting is already so good and it is not rocket science to shift current bikes anyway. how well the new FD would work is an unknown though, since shim 12s di2 FD really is a benchmark product.
I think it is a hardware/mechanical design issue? I seem to recall it being attributed to physical patent issues, when podcasts have discussed it. I do not know what the specific hurdle is though. Maybe also has to do with shimano big chainring design too? not sure.
