Who's correct - Newton or Vector

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blp
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Who's correct - Newton or Vector

Post by blp » Tue Apr 24, 2018 11:59 pm

I rode today with iBike N6 and Garmin Vector 2.

According to the math (http://bikecalculator.com) neither seem correct.

During the ride the N6 was almost always much higher W than the Garmin.

I performed a Cal Ride and did a static calibration of the Garmin (with new batteries) then did my ride and yielded these numbers.

The average with N6 was 177.7W, Garmin 166W, Bike Calculator 137W. However, on climbs, for example, (47-50 minutes), N6 294.6W, Garmin 254W (50-53 minutes in the Garmin file). Calculated with a 9.6 km/h headwind, 301W.

Which is correct, if any?
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activity_2649591712.tcx.zip
Garmin file
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iBike_04_24_2018_1412_4_km_CalRide.ibr
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iBike_04_24_2018_1422_29_km_HiDef.ibr
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Velocomp
Velocomp CEO
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Re: Who's correct - Newton or Vector

Post by Velocomp » Wed Apr 25, 2018 6:17 am

I check these things when I see this kind of question:

1) I look at the overall data to see if the calibration is correct. Yours appears to be just fine

2) I look at measurements on hills, where the accelerometer/weight parameters are most important

3) I look at measurement on flats, where wind sensor/CdA are most important

4) I assume the Velocomp device is providing correct environmental data (speed, slope, wind)

5) I use bikecalculator.com to plug in the hill/flats data

In the flats section, Newton measured 239W, Vector178W, bikecalculator.com 235W (see below)

In the hill section, Newton measured 294W, Vector 255W, bikecalculator.com, 299W (see below)

It looks to me like your Vector is reading low.
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John Hamann

blp
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Re: Who's correct - Newton or Vector

Post by blp » Wed Apr 25, 2018 11:21 am

Thanks John.

I get somewhat different results between N6 and BikeCalculator at different points, some differences greater than others, but the net result is the same, Garmin considerably lower.

I am curious about the calculations over the entire ride. N6 reports average 178W and if I plug in the stats into BikeCalculator, it arrives at 133W (Garmin 166W). Different averaging methods?
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Velocomp
Velocomp CEO
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Re: Who's correct - Newton or Vector

Post by Velocomp » Wed Apr 25, 2018 11:43 am

You can't use bikecalculator.com for long stretches. Their calculations assume that conditions input are constant--clearly, not the case in the real world for a ride of any length! Think of it this way: in the middle of a hurricane, at any given location, the average slope of the water is zero, no matter how much the seas are going crazy

You'll notice that for the analysis I did I picked out short stretches only, where conditions ARE relatively constant.
John Hamann

blp
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Location: Vancouver, BC, Canada
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Re: Who's correct - Newton or Vector

Post by blp » Wed Apr 25, 2018 1:34 pm

John, I had to laugh with the use of a hurricane to illustrate your point. :lol:
Floridians are experts where hurricanes are concerned.

It did make your point clear, I appreciate the info and the chuckle.

Cheers.

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