Well, you've proven to me with your last post that you are intent on ignoring your very own data just to prove to yourself your own imaginary points.

It doesn't take a genius to see that in your 2nd graph, the green (cadence) curve and speed (blue) curve do not correlate, so any bets you're making on saying cadence = speed are totally off on your graphs (duh).

You can still coast on a trainer as well - if you stop pedaling, speed does not go to zero. Dead spots in the pedal stroke could account for some of the variance, although I freely admit that I'm surprised you have so much variance of speed vs cadence in your graphs, which I wouldn't expect. Regardless, it's there, and obviously contradicts any such statements you make about locking cadence to speed (or power).

I'm not the one making stuff up here - in fact, I'm agreeing with everything your graphs show.

That's a good idea to put it on the fly wheel. We're trying to develop a commercial product so we wouldn't be able to have everyone set up their unit like that, but it might be a more accurate way to collect the data for the roll down offsets and then interpolate the points for end users. Maybe have them do 3 roll downs or something.

You're data above though is disheartening. It looks like that even with a roll down test the Fluid 2 would vary a ton in just a short interval. With the KK it looks like after a warm up period it's pretty stable.

Like I said before, I have a fluid 2 sitting in my garage waiting to be ridden on. I'll probably post some excel files back to thread after I've done a few rides. I suspect I'll have the same conclusion that you do - fluid2 sucks for speed to power :).

We're thinking of making our own "Crank Armstrong" that KK has for their tests. We would just hook a motor up to the bottom bracket and set the speed/power output via power taps. That way we could output 300 watts for a few hours and see what happens to the power curve. Same thing at 200 watts, 100, ect. Maybe we could get more data about those "levels" in that other thread.

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CEO at TrainerRoad
Co-host of the Ask a Cycling Coach Podcast

I think what is trying to be explained is that the gearing was different between the intervals, but stayed the same during each interval. Not that the gearing was the same for all the intervals.

If you take any individual interval the speed/cadence are identical. However you can see the power requirements (watts) particularly during interval #4 for example climb throughout the interval, even though the speed/cadence remain the same.

Huh? Are you missing that in the 2nd graph, the run was a constant cadence "sweep" across various cogs? As I explained before, the idea was to vary power and speed to then be able to plot P/V vs. V^2 to derive the virtual CdA and Crr coefficients. Each of the even numbered "laps" was done at a constant cadence in a given gear...and within each of those laps, the gear was held constant and you can easily see that the blue and green lines track exactly the same with a constant offset between them on the graph. The power, however, tended to rise within the higher power level "laps" as compared to BOTH the speed AND the cadence lines.


Strawman. I explicitly said the intervals were constant cadence through each. That means no coasting.


Not likely...especially when you realize that the cadence is triggered on a once per revolution basis.



Well then, here's more graphs for you to agree with...the first being a comparison for cadence vs. speed and power vs. speed for "lap 2" (one of the more "well-behaved" intervals) and the second graph being the same thing for "lap 4". I don't know about you, but judging by the R^2 values of the fits, it sure appears to me that speed correlates better to cadence than it does to power when looking at it on a point by point basis (which I actually am not particularly fond of doing...but, I digress...).

BTW, don't be distracted by the "banding" in the cadence vs. speed plots. Just remember that cadence is reported and recorded in integer values and you'll understand...of course, even WITH that artifact the correlation is significantly better than power vs. speed in BOTH cases.

Lap 2


Lap 4

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http://bikeblather.blogspot.com/

The two different graphs were with 2 different bikes. One geared one not geared

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Styrrell

Yes...they were actually 2 different bikes (not that it mattered), but both had multiple gears. The main difference between the 2 plots was that in the first one I didn't shift (So yes, effectively "ungeared"). Well, mostly anyway...I think I shifted after either the 1st or 2nd interval, but then didn't need to shift the rest of the way (Funny thing...I could probably figure out where I shifted by comparing the speed vs. cadence...funny how that works ;-). And the average load of each 3 minute interval increased by nearly just the right amount I intended to do (~1-2W every 3 minutes) and I was able to just keep pedaling at ~93 rpm (my preferred cadence anyway). It's almost like the load unit was designed for this workout ;-)

In the second plot, I was keeping cadence constant and switching between gears to get large variations in speed and power in an attempt to characterize the Fluid2's load curve. Obviously, if it can't be even remotely consistent within a single 2-3 minute interval, that's going to make characterizing the load curve quite difficult (at least not without a temp sensor on the casing as well! ;-)

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http://bikeblather.blogspot.com/

We are trying to make a "Crank Armstrong" like the one Kurt Kinetic has: http://www.kurtkinetic.com/testrobot.php

We plan on getting a 1HP motor with a speed controller. We would then attach a cog to it and put it behind the bike. We'd put a chain from the motor to our power tap which would be on a bike (in a trainer).

We'd then regulate the power output via the speed controller while looking at the watts outputted by the power tap. By recording the data we should be able to quantify the drift that you and others are experiencing with the Fluid2 (and every other trainer we can get our hands on).

Do you see any problems or have any improvements on this idea? I'd rather attach the motor to the bottom bracket, but that doesn't seem as easy as just putting a cog on the motor. We'd also use a Continental trainer tire to help guard against tire wear that could throw off crr.

Edit: We'd also need a gear reducer. We'll have to do some math about what sort of ratio we need based on the cog we put on the motor and how many RPMS it's at.

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CEO at TrainerRoad
Co-host of the Ask a Cycling Coach Podcast