Robert Chung wrote:
>
> Arrrrgh. Ooops. Sorry. My bad. I GAVE YOU THE WRONG URL.
>
> The right one is:
http://mywebpage.netscape.com/rechung/wattage/cadence/cadence-plot4.png
>
> My apologies. Damn. I also have to apologize for my snide comment about it being funny how some
> people can look at the same evidence and come to different conclusions, because I was pointing you
> to a different plot. Ugh.
Would I be snide to say that rather than "different people looking at the same evidence and coming
to different conclusions," the same person
(me) looks at different evidence and reach the same or similar conclusion?
Well, don't worry, I don't see the same thing, now I see less.
> plot4 is just plot2 with the hill-climbing part labeled. I kept referring to hill and altitude
> change in the text of my replies and how I couldn't have done this part without the altimeter of
> the S710, but the graph I gave you (obviously) didn't have any hill or altitude info on it.
>
> So, let's turn back the clock, if you're willing. What do you see?
The data points are not sequenced, so it is hard (impossible) to tell. For me this topic isn't what
power someone put out at some specific instant or short time period (2.52 & 5 s), but is rather
roughly that of attaining the most Joules out over a "whole race time period" (for both TTs and Hill
Climb TTs: sustainable power). The lack of sequencing is a problem because it can distort the
results in trying to determine what the sustainable power is for some given cadence. For example, a
rider climbing a hill reaches a short steep switchback for which he/she has inadequately low gears,
and so "stomps on it" for 5 seconds. The "stomping" requires unsustainable power output, but the
sample does show high power there. Immediately after exiting the steeper section, the rider sits
down, "spins fast," and does 10 s of recovery riding. The recovery riding will be lower than what
would normally be sustainable, so the power sample is distorted low, for the higher cadence. The low
cadence is distorted high. How many times has this exact scenario occurred? A lot I'll bet, and it
is due to either habit or lack of low gears.
So I don't believe the difference in powers v. cadence as shown in the plot are yet meaningful as
they stand. Was the hill climbing rider really able to put out 350 sustainable watts at 70 rpm, but
only 250 sustainable watts at 95 rpm (-1.5 dB or -39%).
> A guy who seems to show a preference for rpm in the 90's on the flat seems to prefer a very
> different cadence on a hill, and it seems he was producing pretty reasonable power there, too.
> This means that the power-cadence relationship isn't straightforward, and that optimal cadence
> isn't independent of conditions.
It may not be, but the graph by itself doesn't convince me.
> That's it. But you can see why I don't have any argument with your "incentivized preference for
> cadence" (well, except that it's a repugnant neologism).
Heeeyyy... There are no new words there. You can't complain when you use "automagically" and the
recondite "supralinear." I'm trying to get the explicit meaning. I'm eager for better articulation,
so what do you offer?
> I think riders who have been riding for almost any length of time automagically choose something
> pretty close to the optimal cadence given the conditions and constraints facing them. IOW, I tend
> to think that cadence is a response, not a factor (which I wrote in response to Tom somewhere else
> in this thread).
>> I'm not sure why gradient would be too much of a factor (or any factor?) regarding power v. rpm.
>> Maybe it is, but I just don't know why it would be...
>
> Because of force. We all appear to know that given a particular gear, power scales supralinearly
> with rpm.
We all? I don't presume your wrong (at all), but I don't presume the parameters. Explain.
> What many seem not to know (or haven't internalized as completely) is that while force also scales
> supralinearly with rpm on the flat (given a particular gear), as the road tilts up that
> relationship changes. Indeed, for very steep grades, force is almost entirely dependent on gear
> and almost not at all on rpm.
I don't see how this shows why the so-called "optimum cadence" would change for climb v. flat. On a
10sp 12-25 cassette, the average step size is 8.1%. Not that cadence-plot1.png has a lot of
curvature, but
8.1% "fits into" the seemingly preferred range 88 to 108 rpm quite easily (the power is somewhat
flat in that range). The rider can choose the cadence, within 8%, for some given power output
level. If, on the flat, the required force to increase rpm is getting "too high," they can either
back off or just use an easier gear. I suppose I do suspect the power output is quite flat within
+/-4% of "optimum cadence."
I guess I see it as simply the power is delivered via force and rotation of the pedals. What does it
matter if the energy lifts a weight or gets gas molecules moving? How does the body know if the
energy (power*time) is being transferred to potential energy by lifting a weight, or transferred
into kinetic energy of surrounding gases? The legs are simply pushing on the pedals, at a cadence
selectable within 8%.
Like I said before, I believe bike racers have traditionally been overgeared (for climbing) in the
past, and for a justifiable reason. (Or maybe I should say they simply didn't have low gears as a
reasonable choice, because of the tradeoffs.) For this reason, I'm a little skeptical of the hill
climbing data you have shown. One thing that would interest me is showing hill climbing data that
undeniably showed that the sustainable power for Rider X, while climbing at a "low cadence," was
congruent with the sustainable power that Rider X showed while riding the flat at a higher cadence.
While this would not yet prove any kind of "cadence for conditions" hypothesis, it may at least show
that power delivery v cadence is possibly quite flat.
Riders need to be tested for climbs where they have the gears needed to spin up to about 110 rpm at
any point in the climb, and unprejudicedly do runs focusing on narrow ranges. The same is true for
the flats -- try some low cadences too.
So maybe "optimum cadence" changes according to conditions, I am still uncertain why that would be
true. I am concerned that a tradition of climbing at low cadences, and not having low enough gears
to even fairly test this, could be distorting the results. "Spin to win" prejudice in the flats
could be doing the same, although I am not quite as suspicious of this. I don't care how it comes
out, either way.