Please Check O&B Calibration Ride for TT Bike

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NickBean
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Joined: Mon Jul 03, 2017 3:57 pm

Please Check O&B Calibration Ride for TT Bike

Post by NickBean »

Hi John,

I would be grateful if you could please check the attached O&B calibration ride for my TT bike. I haven't done any other rides yet on this bike, as I wanted to check everything is OK before I put in some maximum efforts on my local TT course.

The one thing I did note after completing the calibration ride, is that the distance measured was only 2.2 miles. When I have done calibration rides on my road bikes, using the same O&B course, the distance measured during the calibration rides was 2.5 / 2.6 miles. Don't know if this is anything significant (possible problem with my speed/cadence sensor?), just a thought.

Thanks in advance for your help once again.

Nick Bean
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iBike_06_16_2018_1940_2_Miles_CalRide.ibr
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Velocomp
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Re: Please Check O&B Calibration Ride for TT Bike

Post by Velocomp »

Please post a ride file that occurred after your calibration ride.
John Hamann
NickBean
Posts: 12
Joined: Mon Jul 03, 2017 3:57 pm

Re: Please Check O&B Calibration Ride for TT Bike

Post by NickBean »

Hi John,

Please find attached, as requested, a ride file for my TT bike.

This ride was a 10 mile (as recorded by my Garmin 520) TT, however, my PowerPod only recorded it as a ride of 8.1 miles. Looking at the ride file in Isaac, the tail and head wind numbers also look suspicious - I'm certain the head wind was not 26 mph. The average power reading also seems on the low side when compared to similar effort rides on my other bikes.

I suspect that the cause of the above data problems is my (cheap) speed/cadence sensor for this bike, which may not be working properly.

My PowerPod works great with my two road bikes and I have no reason to believe there is any problem with it.

I would be grateful if you could please check the attached ride file and let me know your thoughts.

Regards,

Nick Bean
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iBike_06_26_2018_1923_8_Miles.ibr
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Velocomp
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Re: Please Check O&B Calibration Ride for TT Bike

Post by Velocomp »

Your guess is dead-on. Your speed/cadence sensor is showing a ton of dropouts.

You'll need to change it.
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John Hamann
NickBean
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Re: Please Check O&B Calibration Ride for TT Bike

Post by NickBean »

Hi John,

As you previously suggested, I bought a new speed/cadence sensor for my TT bike and performed a new O&B calibration ride.

Would you please take a look at the attached ride file and let me know your thoughts and any possible issues. The ride file is approximately 32 minutes including a warm down, however, the important timed part is the first 10 miles up to approximately 25 minutes. My subjective feeling, based on similar efforts on my other bikes, is that the recorded average power of 244 W for the first 25 minutes is a little on the low side. I would have expected something in the region of 270 W to 290 W but, as I said, this is purely subjective.

I felt that my effort was fairly consistent on a flattish course, yet there appears to be a couple of power spikes up to 800+ W, which do not look right - I certainly didn't feel like I was putting out that sort of power at those particular times.

I've also attached the calibration ride if required.

Regards,

Nick Bean
Attachments
iBike_06_27_2018_1557_2_Miles_CalRide.ibr
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iBike_07_04_2018_1924_11_Miles.ibr
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Velocomp
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Re: Please Check O&B Calibration Ride for TT Bike

Post by Velocomp »

The good news is that your new speed sensor is working great.

More good news: your PP is well calibrated.

There are two power spikes, both of which last 2 seconds. In checking your data, there are perturbations in the accelerometer data that caused the power spikes. I agree that the spikes aren't "real" but I don't know why they happened. If you want you can try a hard reset to get rid of them.

There is a section in your first 25 minutes where there is a significant tail wind. Were you drafting?

I don't see anything that would point to low watts problem in your ride file.
John Hamann
NickBean
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Joined: Mon Jul 03, 2017 3:57 pm

Re: Please Check O&B Calibration Ride for TT Bike

Post by NickBean »

Hi John,

Thanks for your reply.

The ride file I supplied was from a solo 10 mile time trial, so definitely no drafting. There was though, as you observed, a fairly significant tail wind in parts of the first 25 minutes of the ride. Conversely, there was also some fairly strong head winds in other parts of the ride.

I may be wrong, but I'm still not totally convinced that the recorded average power of 244 W for the first 25 minutes of the ride is totally accurate. For my road bikes I need somewhere in the region of 270 to 290 W, depending on the wind speed and other factors, to produce an average ride speed of approximately 20 mph.

For the ride file on my TT bike, I was able to average about 24 mph, i.e. an increase in speed of 20% when compared to my road bikes. This increase is undoubtedly due to the aero benefits of a TT bike. Subjectively, I would estimate that I produced a similar sort of effort (i.e. max effort) on my TT bike when compared to a 20 mph ride on one of my road bikes. However, my average power on my TT bike of 244 W for a 24 mph ride is approximately 15% less than that needed for a 20 mph ride on one of my road bikes. So on my TT bike, my average speed increased by 20%, but my average power was down by around 15%. Do you think that those sort of increases in speed and reduction in power are reasonable?

None of the above is very scientific, just my gut feeling.

I'll carry out a hard reset to try and get rid of the power spikes as you suggested.

Thanks and regards,

Nick Bean
Velocomp
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Re: Please Check O&B Calibration Ride for TT Bike

Post by Velocomp »

Hi Nick:

I have a "20-20" rule of thumb: on my road bike, on the flats, I can travel at 20mph with 200 watts applied.

To get up to 270-290W, you'd have to be climbing nearly continuously. Of course that's possible, but I'd like to see the ride file; until I do, I will stick with my 20-20 thought :)

Frankly, your TT watts sound reasonable to me.
John Hamann
Velocomp
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Re: Please Check O&B Calibration Ride for TT Bike

Post by Velocomp »

I used bike calculator.com to check your TT ride. It's a bit tricky to do this because the calculation assumes all values are constant; this is not strictly the case for you (you have some gusts of wind, your bike speed varies slightly, and hill slope changes a bit too).

Using the weight parameters, ride slope, wind speed, and bike speed, for the highlighted section PP is within a few watts of the calculated amount.
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Screen Shot 2018-07-05 at 5.02.49 PM.png
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John Hamann
NickBean
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Re: Please Check O&B Calibration Ride for TT Bike

Post by NickBean »

Hi John,

Thanks for your comments and the data from bike calculator.com to check my TT ride. I'm happy to accept your conclusion regarding my TT ride.

As a point of interest, I seem to be averaging around 18.0 to 18.5 mph for 200W efforts on my road bike rides on a fairly flat course. For 20 mph rides, I seem to require at least 270W - see attached ride files.

Your "20-20" rule of thumb doesn't seem to work for me, although I wish it did.

Regards,

Nick Bean
Attachments
iBike_07_25_2017_1855_23_Miles.ibr
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iBike_05_29_2018_1417_23_Miles.ibr
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