Calibration - What am I doing wrong

[Turbotripper]

I've had my Powerpod for about three weeks and seem to be having trouble getting the calibration right. It's appears to be over estimating the wattage and seems to drift a lot on flat roads. On descents I'm getting wattages that are way too high and on subsequent flat roads the wattages are around 100w too much. (I'm comparing it to a Powertap). I have attached the Powerpod files for you to have a look.

[Velocomp]

There are several things going on:

1) Your PT signal is dropping out quite a bit; there seems to be a problem with your PT

2) Your Crr setting is high. It should be 0.0054 for a road bike

3) Your wind setting is a bit high, too. There is a persistent headwind on the downhill. This will exaggerate downhill watts

4) If you have any change in ride position on the downhill, this too will exaggerate watts

By adjusting your profile slightly your downhill watts are much better. Modified profile and ride file are attached.

But the big problem is the intermittent operation of your PT.

[Turbotripper]

Hi John
Thanks for your reply and the files.
Using the modified profile I did the same route yesterday.
On the climb the watts were exactly the same on the Powerpod and the Powertap - so presumably some of the settings are OK.
However :
1. on the flat while riding on the hoods the power seems to slightly over on the Powerpod
2. on the descent and on the subsequent flat the power was up to 100watts over on the Powerpod. However this was reduced when I sat upright.
Does this suggest that my position is more aero than the profile is set for? Should I change this manually or do another calibration ride on the drops?

I have looked at the power data for the Powertap and it would appear that it's the Powertap to Powerpod that is dropping out as I cannot see any dropping out between the Powertap and my garmin. If it was dropping out from the Garmin 500 surely I would notice it on the unit? Also on another ride this week I noticed that there are a couple of occasions where there are large periods of dropping out between the Powerpod and Powertap but there are no drop-outs between the powertap and the garmin.

Recognising that riding on the hoods and riding on the drops will affect the power estimate/calculation would it be an idea to do two calibration rides (one on the drops and one on the hoods) then have a setting in Isaac where you can tell it to assume that you will be on the drops during descents and on flat terrain above a certain speed or when riding into a headwind?

I have attached the file from the ride.

[GooseRider]

Second the last suggestion:

Recognising that riding on the hoods and riding on the drops will affect the power estimate/calculation would it be an idea to do two calibration rides (one on the drops and one on the hoods) then have a setting in Isaac where you can tell it to assume that you will be on the drops during descents and on flat terrain above a certain speed or when riding into a headwind?

!

[BBQcyclist]

Good idea / suggestion!

[pb21]

I too regularly notice downhill watts being vastly over estimated.

Often I will see the PP saying 300/350+ W when riding relatively easy downhill, and based on exertion and HR I would expect to see considerably less than 200 W.

My position is always the same too, certainly no different than how it varies throughout the rest of the ride.

[Velocomp]

Hi John
Thanks for your reply and the files.
Using the modified profile I did the same route yesterday.
On the climb the watts were exactly the same on the Powerpod and the Powertap - so presumably some of the settings are OK.
However :
1. on the flat while riding on the hoods the power seems to slightly over on the Powerpod
2. on the descent and on the subsequent flat the power was up to 100watts over on the Powerpod. However this was reduced when I sat upright.
Does this suggest that my position is more aero than the profile is set for? Should I change this manually or do another calibration ride on the drops?

I have looked at the power data for the Powertap and it would appear that it's the Powertap to Powerpod that is dropping out as I cannot see any dropping out between the Powertap and my garmin. If it was dropping out from the Garmin 500 surely I would notice it on the unit? Also on another ride this week I noticed that there are a couple of occasions where there are large periods of dropping out between the Powerpod and Powertap but there are no drop-outs between the powertap and the garmin.

Recognising that riding on the hoods and riding on the drops will affect the power estimate/calculation would it be an idea to do two calibration rides (one on the drops and one on the hoods) then have a setting in Isaac where you can tell it to assume that you will be on the drops during descents and on flat terrain above a certain speed or when riding into a headwind?

I have attached the file from the ride.

You're still getting a ton of dropouts on your PT. Furthermore, the data that the PT IS producing looks very peculiar, almost blocky-like (I have a PT on my bike, and its data looks nothing like yours).

I don't trust the PT data, and until I can, I cannot offer any suggestions for fine-tuning your PP profile.

[Aviador76]

Hi guys.

I've just ride my first "Best Accuracy" but there were a lot of wind with gust of wind.

This is my file and I would like if it's a good calibration or I must do it again.

Thanks and regards, Fran.

[Turbotripper]

Hi John
I have done a few rides and am still getting erratic power outputs. I did another calibration ride, this time on the drops but it doesn't seem to have made any difference. I notice the Crr is possibly 'high'. I have attached the files from the calibration ride and from a couple of rides. I would send the garmin/powertap files but the site won't allow it. There is often dropouts between the Powerpod and the Powertap but not between the Powertap and the garmin.