A Simple Power Reading Question



Clandestine

New Member
Feb 20, 2011
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Hey,

I just purchased a used Powertap Pro+ and matched it with a Garmin 500 and just wanted to verify something quickly. I notice that while ridding the watts are jumping all over the place. I think it is calibrated correctly as it reads 0 when I am coasting or not pedaling. Also, going up hill or downhill coasting also reads 0. The only reason I ask is because I just finished all my testing, and before I go head long into training with power I want to ensure that this behavior is normal. Even on a trainer keeping speed and cadence steady shows fluctuations in power readings of greater than 20 - 30 watts.

If this is normal then it begs another question. How do you do intervals if the power readings jump all over from above to below your targeted rates?

Case in point, the other day I was ridding in zone 2 for my heart rate and my power was running anywhere from 145 - 190. Of course when the ride was over I looked at the average at it was in Zone 2. But 2X20s will be tough given the 40 watt spread.

Any thoughts would be very helpful...
 

Felt_Rider

Well-Known Member
Oct 24, 2004
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On the road I use a PT / Edge 705 combination.

Suggestions:
I set my display for 3 seconds to help smooth it out a little. I think there is a display setting for 30 seconds for more smoothing.

Even when I train indoors with a different PT system using the little yellow PT Cervo computer I set my display to Avg watts rather than looking at real time wattage. Using either the KK trainer or rollers I know what my speed needs to be on either in order to achieve my interval goal. Outdoors makes it more challenging because of rolling terrain, traffic, dogs and other issues, but I still look at the Avg over the span of time rather than watch the jumpiness of real time wattage. When I upload my data to WKO+ it typically hits what I desired to hit for the training IF.

Another suggestion: (I may be misreading your post)
Forget using heart rate zones if you are using a much more accurate measurement of power.
I was convinced a few years ago by discussions on this forum to stop using my HR strap altogether. I have not worn one in several years.
 

Clandestine

New Member
Feb 20, 2011
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Thanks Felt_Rider,

I found that the Garmin 500 has a 3s Avg and 30s Avg which I added to the display. I'll give it a shot tonight as I am doing hill intervals. Thanks for the tip...
 

lanierb

New Member
Aug 12, 2004
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Totally normal. It happens both because your legs are changing their power output erratically and also because of the way the power meter time averages (which can take into account a different number of "downstrokes" each second). As Felt said, use the Avg power 3s display, as the current power bounces around too much.
 

Felt_Rider

Well-Known Member
Oct 24, 2004
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As a bonus Garmin will be adding TSS / NP / IF as a firmware update in a few months. /img/vbsmilies/smilies/smile.gif

Might be useful in some cases.
 

Clandestine

New Member
Feb 20, 2011
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Worked perfectly... I hope next year not to be just pack fodder. Hence, the reason for a powermeter and structured training this winter. Think I am on the right track. Signed up for the trainingpeaks site to manage my training schedule and keep me honest on my training hours. Read the Cyclist Training Bible to get a good understanding of periodization and training. Did my tests to find my power levels and my 20min TT for FTP. Read a ton of the forums here on SST, FTP, and the wonderful 2x20s. Armed with knowledge and the right equipment, things are going to be better next year.
 

Felt_Rider

Well-Known Member
Oct 24, 2004
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Originally Posted by Clandestine .

Read a ton of the forums here on SST, FTP, and the wonderful 2x20s. Armed with knowledge and the right equipment, things are going to be better next year.
No doubt
Sounds like you are armed with the right stuff. Now it comes down to time spent training and application of those principles as it is for me as well.

Best wishes