When I am coasting downhill, I get a power reading of zero, as one would expect. However, if I spin the pedals to keep my legs moving and the freehub is still frewheeling, ie no pedal input force, I get varying power readings up to 280W depending on how fast the cadence. Say 30 RPM I get 50W, 60 RPM I get 250W. It definitely skews the ride data in the mountains.
Why is this? Is there a way to zero this out? Do I need to redo the cal ride and / or coast down?
power when coasting
Re: power when coasting
When you are coasting downhill and spinning your legs, the iBike's zero cadence = zero power "rule" is bypassed.
Since bike speeds are generally high on downhills, the opposing force of wind increases significantly. To get zero power, this opposing wind force must be precisely offset by the "aiding" forces of downhill slope and bike acceleration.
Finally, to measure the opposing wind force precisely, your body has to be in the exact same ride position as it is normally. If you go into a tuck (to rocket down the hill faster), the iBike will think that your higher bike speed is the result of pedaling harder.
If your iBike is exactly calibrated, and your ride position is perfect, then you can freewheel on downhills and get readings reasonably close to zero. Otherwise, you might see the kind of results you are experiencing.
We are working on an Isaac feature that will detect and correct this situation (non-zero watts on downhill freewheels).
In the mean time, the surest way to avoid this annoyance is to keep cadence at zero on fast downhills.
Since bike speeds are generally high on downhills, the opposing force of wind increases significantly. To get zero power, this opposing wind force must be precisely offset by the "aiding" forces of downhill slope and bike acceleration.
Finally, to measure the opposing wind force precisely, your body has to be in the exact same ride position as it is normally. If you go into a tuck (to rocket down the hill faster), the iBike will think that your higher bike speed is the result of pedaling harder.
If your iBike is exactly calibrated, and your ride position is perfect, then you can freewheel on downhills and get readings reasonably close to zero. Otherwise, you might see the kind of results you are experiencing.
We are working on an Isaac feature that will detect and correct this situation (non-zero watts on downhill freewheels).
In the mean time, the surest way to avoid this annoyance is to keep cadence at zero on fast downhills.
John Hamann
Re: power when coasting
Thanks John. That makes sense 
. I do get it.
I redid my cal ride and then did a casual ride. The Watts seemed more 'correct' and on the downhill, zero cadence = zero W and slow cadence downhill = zero W.
It is very clear to me that a careful, accurate cal ride is critical.
. I do get it.I redid my cal ride and then did a casual ride. The Watts seemed more 'correct' and on the downhill, zero cadence = zero W and slow cadence downhill = zero W.
It is very clear to me that a careful, accurate cal ride is critical.
Re: power when coasting
Velocomp said:
We are working on an Isaac feature that will detect and correct this situation (non-zero watts on downhill freewheels).
John,
I hope you will give a choice to turn off this new feature as some of us use it to check things, like precise calibrations, etc.
Thanks,
Russ
We are working on an Isaac feature that will detect and correct this situation (non-zero watts on downhill freewheels).
John,
I hope you will give a choice to turn off this new feature as some of us use it to check things, like precise calibrations, etc.
Thanks,
Russ