Hi,
I've gone through calibrating my Newton+ with a power tap and I'm interested in interpreting the data available with the power meter comparison tool. The power tap is a loner and I might not have access to it all the time. Anyhow here's a sample from a ride I did last night:
IBIKE STATS
------------------------------------------------------------------------
Ride: Distance: 65.19 km
Duration: 2:07:03
Start Time: 28/06/2012 5:13:42 PM
Avg Temper: 25 degC
Start Pres: 1007.2 mbar
Avg CdA: 0.364 m^2
Crr: 0.00400
Speed: Avg: 30.78 km/h
Max: 50.5 km/h
Wind: Avg: 27.97 km/h (dist-based)
Max: 43.5 km/h
wrt Road: Min: -26.2 km/h (- is tail; + is head)
wrt Road: Avg: -4.34 km/h (dist-based)
wrt Road: Max: 11.1 km/h
Slope: Min: -7.03%
Avg: 0.00% (dist-based)
Max: 5.48%
Elevation: Min: 660 m
Avg: 710 m
Max: 766 m
Cadence: Avg: 86.3 rpm (ignoring zeros)
Max: 115 rpm
HR: Avg: 133.6 bpm (ignoring zeros)
Max: 164 bpm
------------------------------------------------------------------------
IBIKE COMPARED TO ANALYTICCYCLING.COM
------------------------------------------------------------------------
Plug the following parameters(*) into the static forces calculator at
http://www.analyticcycling.com/ForcesPower_Page.html
Effective Frontal Area(#) = 0.729 m^2
Drag Coef (keep the default) = 0.5
Air Density = 1.084 kg/m^3
Weight of Rider and Bike = 100.2 kg
Coef of Rolling Resistance = 0.0040
Slope = 0.00002 rise/run
Speed = 8.551 m/s
Pedal Cadence = 81 rev/min
Crank Length(**)
Effective Pedaling Range(**)
Compare the avg power result from Analytic Cycling to the comparable
result from the iBike 3 calculation engine:
Propulsion Power = 157.26 W <---<<< compare to AnalyticCycling(##)
Rider Power = 160.47 W
* The AnalyticCycling calculator assumes perfectly calm wind
conditions. Further, it does not account for any accelerations or
decelerations.
# (Drag Coefficient) x (Effective Frontal Area) = CdA
** Crank Length and Eff Pedaling Range do not factor into the avg
power calculation
## The AnalyticCycling calculator ignores drive train losses.
------------------------------------------------------------------------
POWER METERS COMPARED TO EQUATIONS OF MOTION
------------------------------------------------------------------------
Ride File Min Pow Avg Pow Max Pow
AnalyticCycling.com 154.24 160.47 163.67
Speed Elev 0.00 186.74 792.95
Speed Wind Elev 0.00 153.72 640.23
Speed Wind Slope 0.00 152.96 743.76
Newton+ 0.00 154.03 1041.81
PT ANT+Sport (iB DFP 0.00 191.15 869.00
------------------------------------------------------------------------
R^2
------------------------------------------------------------------------
| Newton+|PT ANT+Sp
Newton+| 1.000| 0.550
PT ANT+Sport (iB | 0.588| 1.000
R^2 calculation is row w.r.t. column.
As you can see there is there are some differences between the power reading of the two especially at the high end. Also what numbers should I be looking for in the R^2 values? My assumption is they should be a lot closer if the calibration of the Newton is good.
From my calibration ride I have the following values:
Cm 1.02
Aero: 0.272
Wind Scale: 0.751
Cda: 0.362
Friction: 9.967
Riding Tilt: -0.6
Crr: 0.0040
I've also attached the calibration file.
Comments and suggestions as to how I can adjust thing to get my Newton readings closer to the power tap reading would be greatly appriciated.
I would like to suggest the software documentation could stand a major update. The file provided is for version 5.x released in 2010 and for a number of the tools and analysis options the documentation is very thin or non-exsitant. I understand a lot of effort has been put into the new hardware but out data documentation for the analysis software is really frustrating and makes it hard to get the most out of the device.
Cheers!
Newton Compared to Power Tap
Newton Compared to Power Tap
- Attachments
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- IbikeCal20120626.ibp
- (446 Bytes) Downloaded 260 times
Re: Newton Compared to Power Tap
Please post both your iBike file and your PT file. Note that, if your PT is wireless, your DFPM information should be in your iBike file.
John Hamann
Re: Newton Compared to Power Tap
Here's the ride file.
- Attachments
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- iBike_06_28_2012_1713_65_km.ibr
- (799.53 KiB) Downloaded 273 times
Re: Newton Compared to Power Tap
I looked at your ride file. Notice that there are blue "icicles" consistently below your white speed. This is a strong indicator that the Cal Ride was "off".
In fact, using the Analyze/Check Calibration, and assuming that average wind speed was zero for the total ride, your calibration is way off.
Applying the recommendation of the Check Calibration, you'll see there is excellent agreement with your PT.
In fact, using the Analyze/Check Calibration, and assuming that average wind speed was zero for the total ride, your calibration is way off.
Applying the recommendation of the Check Calibration, you'll see there is excellent agreement with your PT.
- Attachments
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- ride file as sent
- Screen Shot 2012-07-01 at 6.39.37 PM.png (68.22 KiB) Viewed 4687 times
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- check calibration screen
- Screen Shot 2012-07-01 at 6.40.20 PM.png (66.01 KiB) Viewed 4686 times
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- After correcting with Check calibration
- Screen Shot 2012-07-01 at 6.40.52 PM.png (169.17 KiB) Viewed 4688 times
John Hamann