How accurate is the iBike?

[coachboyd]

That's probably the most frequently asked question out there. People just want to know how well does this work.
So, I went out on a ride with my iAero, the new Quarq Cinqo, and a Power Tap. The results are in the following pdf file.
And a note, some of you are familiar with the wattage group over at google groups. I did this ride to answer a question for a lot of people there. I told them I would go out and ride the next day with all three power meters and show the results. This was the results from that ride the next day. I didn't go digging through files looking for the best possible one, this is VERY typical of all my rides.

http://www.ibikesports.com/documents/Jo ... alysis.pdf

Coming soon, I will have lots of rides with all three power meters going, including group ride situations with lots of drafting.

[Tom_Anhalt]

Thanks Boyd. That's a good summary. Do you mind if I ask what PT model you used on that ride? Based on the couple of dropouts you had there, I'm assuming it was a wireless model, correct?

Also, the first anomaly you showed seems to indicate that the power reading being recorded by the iAero from the CinQo basically got "stuck" at 350W for a period of time. Do you have any idea if that's a caused by an issue with the CinQo output, or perhaps by the wireless mount of the iAero?

BTW, I personally like to look at the reported average powers over the default durations that WKO+ calculates rather than just the overall ride average. That seems to do a better job of indicating how well the power meters "match up" over various durations. A point-by-point type analysis as shown from the iBike2 software output (the regression coefficients) can sometimes be affected by the "phasing" of the PM outputs. Due to the differences in how the power signals are processed and recorded, there are sometimes "leads" and "lags" and a pt-by-pt analysis won't always capture that.

[rruff]

BTW, I personally like to look at the reported average powers over the default durations that WKO+ calculates rather than just the overall ride average. That seems to do a better job of indicating how well the power meters "match up" over various durations.

I agree. The most convincing comparison would be independant analysis of the 3 data sets using WKO+ over an extended period of time... since this is what most riders use a power meter for. If you can show that an iBike yields the same useful data for tracking training stress and performance (etc), then a *very* good case can be made for its viability.

BTW... a lower reading with the PT is normal since it does not include drivetrain friction... ~6-10W lower would be normal.

[coachboyd]

Thanks Boyd. That's a good summary. Do you mind if I ask what PT model you used on that ride? Based on the couple of dropouts you had there, I'm assuming it was a wireless model, correct?

Also, the first anomaly you showed seems to indicate that the power reading being recorded by the iAero from the CinQo basically got "stuck" at 350W for a period of time. Do you have any idea if that's a caused by an issue with the CinQo output, or perhaps by the wireless mount of the iAero?

BTW, I personally like to look at the reported average powers over the default durations that WKO+ calculates rather than just the overall ride average. That seems to do a better job of indicating how well the power meters "match up" over various durations. A point-by-point type analysis as shown from the iBike2 software output (the regression coefficients) can sometimes be affected by the "phasing" of the PM outputs. Due to the differences in how the power signals are processed and recorded, there are sometimes "leads" and "lags" and a pt-by-pt analysis won't always capture that.

Yes, I was using a wireless PT wheel. I will be doing more three way comparison rides soon.
The Cinqo I had had an old firmware on it, so it would get "stuck" on a certain wattage at times. I sent it back in August for a fine tuning and for them to see how it was holding up to a riding and racing schedule and they upgraded the firmware. It still very occasionally happens, but maybe once or twice per ride.

I forgot that I had this graph from the ride, but I took screenshots of the mean maximal power over time for all three units. Here is the side by side by side readings of those.

[iodaniell]

Boyd, what was the Normalized Power (NP) for each device, if you don't mind me asking?

[Tom_Anhalt]

Great...using that output, here's the types of plots I like to make for each ride:

BJ_3Way.jpg (290.71 KiB) Viewed 5322 times

Then, after looking at a bunch of files over a longer period, you can get a better idea of the "long term" agreement, for example like here where I was comparing an Ergomo to a PT and a Polar to try to see how much to adjust the slope of the Ergomo:

EP_PT_Polar_week.jpg (269.43 KiB) Viewed 5319 times

That pretty much helps to see where the "outliers" are in the outputs. I also have done similar plots comparing the ride NP values over a long term. I figure that the things I'm REALLY concerned about are how each PM affect my MMP curve in WKO+, and how the TSS values compare since that's my input into WKO+'s Performance Manager Chart.

[coachboyd]

Boyd, what was the Normalized Power (NP) for each device, if you don't mind me asking?

I have the results for the 20 minute NP for each device
iBike: 287
Quarq: 297
PT: 290

I can look it up for the whole ride if you want, but 20 minutes paints a better accuracy picture.