stages power meter.
thks

What power meter were you using? Did you send the power meter 3 consecutive "zeros"? Were the offsets all the same?

I've been incorporating a 3-zero protocol lately for the power meters we use when aero testing. It's surprising how often the first zero sent to almost any power meter will be different than the subsequent ones. Try and see.

That may be the source of many aero "puzzles", btw.

Given all of the above...is this data sufficient for (any) purpose?

What power meter were you using? Did you send the power meter 3 consecutive "zeros"? Were the offsets all the same?

I've been incorporating a 3-zero protocol lately for the power meters we use when aero testing. It's surprising how often the first zero sent to almost any power meter will be different than the subsequent ones. Try and see.

That may be the source of many aero "puzzles", btw.

Within what time frame?

When I do roller testing of tires, I'm setting the zero on a Quarq every 4-5 minutes and the number returned is typically within 2-3 units (and mine doesn't even have the 10k temperature compensation).

I zero again when I get out to the testing venue but I still usually add an extra lap for the first run of the day that I intend to toss out. For some reason my very first lap often tends to be noisier than subsequent laps. I used to worry about it and try to figure out why but now I just do that first lap as a "reconnaissance" lap to spot my line and then I toss it.

It's sufficient for learning that you should probably use a speed sensor and you need to zero your PM. The VE profiles for the laps look pretty consistent. Was this an out-and-back with roughly 4 meters of elevation change from the start to the turnaround? Something odd happened on lap 2 of run 2 -- did a couple of cars pass or something? Regardless, I'd ignore that particular lap, though the rest of the laps seem okay. This is one of the good things about this particular protocol -- if you get something like a passing car or you have to hit the brakes or some other interruption, you can sometimes ignore that bit but salvage the rest of the run.

The very first loop I used was a 3.2km long test loop. Slightly longer than ideal but that's what I had available to me at the time.

The Stages might not be the best PM for this particular application, but I don't see anything grossly wrong that would invalidate it.

Whether 0.31 m^2 for CdA is worrisome depends on how tall you are. You've set all-inclusive mass at 92 kg so I'm guessing you're not tiny. In addition, if estimated Crr is low, your estimated CdA will be high, so if your tires had higher rolling resistance it'd drop your CdA estimate a little.

This is a good start.

Within what time frame?

When I do roller testing of tires, I'm setting the zero on a Quarq every 4-5 minutes and the number returned is typically within 2-3 units (and mine doesn't even have the 10k temperature compensation).

3 quick zeros with a 30-sec time-frame.



You have a good N=1 power meter. This year, I've seen maybe 60-70 different power meters while aero testing and I need to zero 3x and make sure that the last 2 zeros return a similar offset. This is true across all power meter brands that I've seen:
SRM, P2max, Quarq, Powertap hub, Powertap P1 pedals

Yesterday's run, for instance, had a rider with an SRM. We'd hit it with a zero and it would return something like: 532, 527, 528, 528.

You probably already know this, but the units on the returned zero can vary quite a lot between different brands of powermeters (and even within the same brand depending on the slope). IIRC each unit on Power2max is something on the order of 1-2W (at a cadence of ~90 rpm - but depends on the slope of the individual unit), whereas for a Quarq or SRM it is on the order of 0.3W (but slope-dependent on the SRM at least).

Hi Andy,

Have you tried using a "Headwind" column into Aerolab recently ? I must be doing something wrong, it is being ignored.

Lately no, but I was "involved" in getting headwind into Aerolab in the first place. :-)

I think you have to spell it right. "headwind" is what I just found in the code:
https://github.com/...9C%93&q=headwind

thanks

I'll play a little more. I tried "Headwind" and "headwind". If I put it in the last column it gets ignored. If I put it right after "Km/h" it gives me an Error message "Insuffucient valid data". I am basing the rest of format on what GC exports to .csv

Minutes, Torq (N-m), Km/h, headwind, Watts, Km, Cadence, Hrate ID, Altitude (m)
0.0166667, 0, 11.1852 ,1.1, 120, 0.00309, 22, 93, 0, 1.20001

Cool, I didn't know they had implemented headwind! Let me know if you get it to work.

To go a step further is would be super cool if you could just input a wind speed and direction and then it would calculate the headwind (and apply it) using that information combined with the direction of the ride at any point (using GPS coordinates). I think it could work OK as long as the course you are riding is not too twisty or technical. And yaw angle could then also easily be added - but now we're getting into BBS territory :)

I noted what Robert said about the sensitivity of the Cda to the Crr. [..]
But still needs careful confirmation which I will do some time soon.

I need to poke around more but at first glance

- Headwind is supported
- You can't import it via .csv, but you can add the column in the editor
- It will export to .json
- It seems to import from json

JSON is a JavaScript representation of your data. Great for manipulating in a browser or a bit of code. Not so good for people, even with a decent editor.

Getting airspeed data in there works wonders! May I ask what you were using to measure it? It took me months to get good quality data.