Initial calibration in windy conditions
Posted: Mon May 02, 2016 11:38 am
I have another thread at the moment where I discussed issues with mounting the PowerPod to my TT bike. I have parked that idea for the time being until I get the TT mount, which I think is due in a couple of weeks. That thread is here: http://www.ibikeforum.com/viewtopic.php?f=93&t=3537
In the meantime, I thought I'd see how well I could get the PowerPod to work mounted on the handlebars of my road bike, which I suppose is how 99% of people will use it. I went out for a two hour ride today, the first few minutes the PowerPod recalibrated itself, and then I just carried on riding. I have a DFPM (Classic Power2Max mounted on Rotor 3D+ cranks) and two Garmin head units so I can see how both meters are responding. It's a windy day here today, and because of the route I rode, the few minutes spent in calibration mode were mostly into the wind. Once it had calibrated, I was pleased to see the PowerPod tracking quite close to the DFPM, generally 5-10w above the DFPM reading on average, although with 3s rolling power displayed on both head units as well, it wasn't always close. But I tracked the overall average for the whole two hours after the calibration, and initially it tracked very well. The wind conditions during that spell were similar to the period of calibration - mostly headwind.
However, when I turned to come back home (via a mostly different route), the PowerPod began to significantly over-read in tailwind sections, sometimes it was reading around 400w where the DFPM was reading around 200w. This occurred when I was travelling quite quickly (e.g. 27-28mph) along a mostly flat round, aided by a strong tailwind. Isaac thinks that I was drafting during this period. The over-reading is characteristic, but reduced, almost all the way home, and by the time I got back, the overall average for the whole two hours was 30w higher on the PowerPod (232w vs 202w).
What to make of that? I wonder if the PowerPod is sensitive to the conditions under which it is calibrated? i.e. if you calibrate it into a headwind, it will read well into a headwind, but not a tailwind? That's certainly how it appears from today's ride.
I merged my DFPM file into the .ibr file to check the calibration. It recommended I change the wind scaling from 1.325 to 1.033. Isn't that a little low? I've attached the .ibr with the DFPM embedded, and also there's a photo of the PowerPod mounted to my bike.
The main thing I am wondering is the calibration conditions. I haven't read anywhere that it should be done in stable conditions, or that it's a problem to ride just one way. It's ok for me to check as I have a DFPM, but my friend has just ordered a PowerPod and doesn't have a regular power meter, so I'd like to be able to advise him on his calibration.
In the meantime, I thought I'd see how well I could get the PowerPod to work mounted on the handlebars of my road bike, which I suppose is how 99% of people will use it. I went out for a two hour ride today, the first few minutes the PowerPod recalibrated itself, and then I just carried on riding. I have a DFPM (Classic Power2Max mounted on Rotor 3D+ cranks) and two Garmin head units so I can see how both meters are responding. It's a windy day here today, and because of the route I rode, the few minutes spent in calibration mode were mostly into the wind. Once it had calibrated, I was pleased to see the PowerPod tracking quite close to the DFPM, generally 5-10w above the DFPM reading on average, although with 3s rolling power displayed on both head units as well, it wasn't always close. But I tracked the overall average for the whole two hours after the calibration, and initially it tracked very well. The wind conditions during that spell were similar to the period of calibration - mostly headwind.
However, when I turned to come back home (via a mostly different route), the PowerPod began to significantly over-read in tailwind sections, sometimes it was reading around 400w where the DFPM was reading around 200w. This occurred when I was travelling quite quickly (e.g. 27-28mph) along a mostly flat round, aided by a strong tailwind. Isaac thinks that I was drafting during this period. The over-reading is characteristic, but reduced, almost all the way home, and by the time I got back, the overall average for the whole two hours was 30w higher on the PowerPod (232w vs 202w).
What to make of that? I wonder if the PowerPod is sensitive to the conditions under which it is calibrated? i.e. if you calibrate it into a headwind, it will read well into a headwind, but not a tailwind? That's certainly how it appears from today's ride.
I merged my DFPM file into the .ibr file to check the calibration. It recommended I change the wind scaling from 1.325 to 1.033. Isn't that a little low? I've attached the .ibr with the DFPM embedded, and also there's a photo of the PowerPod mounted to my bike.
The main thing I am wondering is the calibration conditions. I haven't read anywhere that it should be done in stable conditions, or that it's a problem to ride just one way. It's ok for me to check as I have a DFPM, but my friend has just ordered a PowerPod and doesn't have a regular power meter, so I'd like to be able to advise him on his calibration.
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