Inconsistencies between PowerPod and Powertap G3/GS hub

[scuba_cyclist]

I have always suspected PowerPod power values to be a bit low, a fellow rider offered to pace me for part of a ride today - during part of a climb.

Attached please find the .ibr file for today's ride, along with our respective tcx files. Ride is very casual, I tend to ride a bit faster, focus should be on the end of second major climb - approximately minutes 53 - 56. Specifically, rider claimed a power reading of approximately 240 watts from his Powertap (as read by a Garmin wrist-mount device), output from the PowerPod (as read by my Garmin Edge 1k) was increasing, in the mid to high 100's.

One major difference: other rider claims to weigh 170 lbs, I am 210 lbs; if anything, this suggests my power output should be GREATER to keep pace - currently the opposite.

I would be most grateful for any assistance to explain this variation, appropriate actions.

[Velocomp]

There are several things going on:

1) Your PP is paired to a Quarq CinQo power meter. Did you know this?
2) The Quarq readings (visible when the View DFPM box is checked) are bizarre.
3) It looks like you are on a mountain bike. I suspect this because your tilt correction changes radically when you descend the hill and then ascend it the second time
4) When you ascend the hill the second time, your PP spends the first few minutes of the climb correcting for the fact that your bike's front fork is in a different orientation compared to the ascent. You can see this by the dip, then increase, in watts, even though you are climbing a constant hill.
5) In the last couple of minutes of the second climb, PP tilt calibration is stable. Your PP watts are 249 and slope is 7.90%. PP's slope squares with your elevation change of 91 feet over this period. Your PP measures 249W and aero coach.au reports 250W for the same region

http://www.aerocoach.com.au/power-from-speed/

In sum, if you lockout your fork during these steep ascents and descents you should get good results from your PP.

PS: you might want to do a new sensor pairing, when the Quarq is not around. You will have to do a new cal ride afterwards.

[scuba_cyclist]

Thank you, John. Please see comments below.

There are several things going on:

1) Your PP is paired to a Quarq CinQo power meter. Did you know this?
NO IDEA where this came from. I upgraded to the Garmin 010-12104-00 when purchasing the PP, installed the speed sensor on the front wheel as instructed.
2) The Quarq readings (visible when the View DFPM box is checked) are bizarre.
Would be grateful for guidance on how to perform a new sensor pairing, as I do not own another power meter, exclusively Garmin sensors.
3) It looks like you are on a mountain bike. I suspect this because your tilt correction changes radically when you descend the hill and then ascend it the second time
Nope - Ritchey breakaway roadie - steel frame with carbon fork, aluminum stem. Perhaps a mounting issue? I use a Bike Stem Mount Holder for my Garmin computer (image attached), GoPro mount underneath for PP. As many of my rides are early, ride year round, I use an Aluminum Dual Twin Mount Adapter Compatible (image attached) for PP and light; perhaps alignment is off? PP not adequately secured? Any suggestions on confirming proper alignment? Local roads are not in the best condition - lots of bumps along the way.
4) When you ascend the hill the second time, your PP spends the first few minutes of the climb correcting for the fact that your bike's front fork is in a different orientation compared to the ascent. You can see this by the dip, then increase, in watts, even though you are climbing a constant hill.
5) In the last couple of minutes of the second climb, PP tilt calibration is stable. Your PP watts are 249 and slope is 7.90%. PP's slope squares with your elevation change of 91 feet over this period. Your PP measures 249W and aero coach.au reports 250W for the same region

http://www.aerocoach.com.au/power-from-speed/

In sum, if you lockout your fork during these steep ascents and descents you should get good results from your PP.

PS: you might want to do a new sensor pairing, when the Quarq is not around. You will have to do a new cal ride afterwards.

[Velocomp]

1) Wake up your speed/cadence/HR sensors. Confirm with your bike computer that they are working. Then, press-hold PP button for 4 seconds, until its light starts to flash green. Sensor pairing is complete when light goes solid green, then off.

2) You will have to do a new cal ride after the new sensor pairing.

3) Your PP is rotating on your mount system; this is the cause of your watts discrepancies. Make sure your PP is solidly attached to the mount, and that NOTHING can rotate.

[scuba_cyclist]

Thank you, John.

Will repair sensors, perfrm new cal ride, do my best to prevent rotation.

Would be most grateful for any guidance on proper positioning - particularly with the extra twin mount adapter.

[Velocomp]

Thank you, John.

Will repair sensors, perfrm new cal ride, do my best to prevent rotation.

Would be most grateful for any guidance on proper positioning - particularly with the extra twin mount adapter.

Please post photos of your PP attached to your bike, with detailed views of the mount.

[scuba_cyclist]

Thank you, John.

Was able to fit in re-pairing of sensors, new cal ride this afternoon; PowerPod created the 3 attached files.

Would be most grateful for your comments.

[scuba_cyclist]

Thank you, John.

Will repair sensors, perfrm new cal ride, do my best to prevent rotation.

Would be most grateful for any guidance on proper positioning - particularly with the extra twin mount adapter.

Please post photos of your PP attached to your bike, with detailed views of the mount.

Attached please find some images, with and without the PowerPod. All mounts are aluminum, feel very secure - no "give".

[scuba_cyclist]

Attached is PP file from the first ride after re-pairing sensors - would be most grateful for your comments.

Corresponding .tcx file is too large to attached, uploaded to a Dropbox folder: https://www.dropbox.com/s/j5wv5vo8mhi58 ... 9.tcx?dl=0

[Velocomp]

This is better but I am still seeing evidence of flexing.

I think you would do much better if you used our standard handlebar mount and attached your PP to it...

Your rides are bringing back great memories to me. I used to live next to UCSD and worked at (the then-named) General Atomic. I love your part of the world!

By the way, you can merge your .tcx files into your ride file with the command "File/Merge File..." Eventually you'll be shown a window where you can choose which data to merge. De-select the DFPM box, and keep everything else. You can then save the merged file with your GPS data in it!