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Stages vs. PowerTap power meter comparison

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Stages vs. PowerTap power meter comparison

Old 09-22-14, 12:36 PM
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RoboCheme
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Stages vs. PowerTap power meter comparison

I've been using a PowerTap (PT) PRO power meter for the last four years. I don't race, but I do use cycling to stay in shape and a power meter keeps me honest on how much effort I'm putting into it.

Anyway, a few months ago I made the switch to a disc brake road bike (a Volagi Liscio) and I added a Stages power meter. Compared to my PT results, the Stages PM seemed like it was quite comparable, This observation was based on looking at elapsed time and average power for several different Strava segments.

I was still curious on what exactly is the difference between the two PMs and since I have two Garmins (a 705 and a 510), I decided to do a test. I moved the Stages crank back to the old bike (a Scott CR1) so that I had the 705 reading the output from the PowerTap and the 510 reading the output from the Stages. I checked that they weren't inadvertently reading the same pm by doing some single leg pedaling.

After calibrating both, I did a nice, hour-long climb up the local mountain (Mt. Diablo), not to the top, but long enough to get a reasonable power curve. I then loaded both outputs onto Strava and compared the outputs. Basically, after the 15 second point on the power curve, the watt numbers were within 1-3 watts of each other, with the 510/Stages output always slightly lower than the 705/PowerTap.

Also, during the ride I was watching the 3 second and 30 second averaged power outputs and they were very close to the corresponding outputs on the other Garmin.

I hope this helps if anyone is considering either PM.

Cliff
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Old 09-22-14, 01:25 PM
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How about some sprints and compare peak output, 5s output, etc.?
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Old 09-22-14, 01:36 PM
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Originally Posted by robabeatle View Post
How about some sprints and compare peak output, 5s output, etc.?
You're welcome. I don't sprint, but here are the numbers for the first 15 seconds. The first number is the PT.

2 sec - 413, 350
3 sec - 391, 348
4 sec - 380, 338
5 sec - 364, 334
10 sec - 316, 313
15 sec - 281, 278
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Old 09-22-14, 02:00 PM
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Interesting.
Any chance you can post strava plots for both along with elevation profile?
I have PT but was seriously looking at Stages as well due to it's simplicity and cost.
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Old 09-22-14, 02:05 PM
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Your drivetrain is magically adding watts

Really seems like a calibration issue. the hub based PT should read lower than your crank based Stages. Probably because the Stages is interpolating total power off one (non drive side) sensor, and your output is asymmetric. As it goes through more cycles it gets closer.
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Old 09-22-14, 02:20 PM
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Originally Posted by robabeatle View Post
How about some sprints and compare peak output, 5s output, etc.?
Why? Power readings are irrelevant when you're doing that type of training.
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Old 09-22-14, 02:21 PM
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Originally Posted by delcrossv View Post
Your drivetrain is magically adding watts

Really seems like a calibration issue. the hub based PT should read lower than your crank based Stages. Probably because the Stages is interpolating total power off one (non drive side) sensor, and your output is asymmetric. As it goes through more cycles it gets closer.
Without actually measuring OP's right/left power balance to a very high degree of precision, there's no way to know what reading is "more" correct.
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Old 09-22-14, 02:26 PM
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Originally Posted by achoo View Post
Without actually measuring OP's right/left power balance to a very high degree of precision, there's no way to know what reading is "more" correct.
Correct. But since the PT is higher, and integrates both legs' output, if I had to guess, I'd say the Stages is reading low.
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Old 09-22-14, 02:42 PM
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I was just interested in verifying that the Stages was in the ballpark. Given the data, I think that it was more than acceptable. Whether the PT is the right no. or the Stages is the right no., in my mind is irrelevant. I just wanted to assure myself that I can compare the Stages results to the past PT results and see how they decline with my advanced age. If you care about the absolute no. being right, probably a SRM or a Quarq is the way to go.


Iron Horse, here's my Strava ride. It shows the Stages output. Add one to three watts for the PT output.

Bike Ride Profile | PM Test II - Stages vs PT near Walnut Creek | Times and Records | Strava
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Old 09-22-14, 02:57 PM
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Can you please upload PT ride as well?

Without seeing both side by side it is hard to draw any conclusion.
It's kind of rare test - I'm sure many will appreciate it.

Looking at Stages design approach I can see how they can drop price quite a bit to the point where it will be silly not to buy one if you even remotely into cycling.
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Old 09-22-14, 03:01 PM
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Originally Posted by IronHorseRiderX View Post
Can you please upload PT ride as well?

Without seeing both side by side it is hard to draw any conclusion.
It's kind of rare test - I'm sure many will appreciate it.

Looking at Stages design approach I can see how they can drop price quite a bit to the point where it will be silly not to buy one if you even remotely into cycling.
Actually, I can't even though I still have the file. Strava thinks correctly that it's the same ride. I initially loaded the PT now., wrote them down the old way (on a piece of paper), deleted the file and then loaded the Stages file.

I initally intended to load one of them on my wife's Strava account, but she's not premium so there's no power curve.
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Old 09-22-14, 03:04 PM
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Strava is easy to fool.
Find original ride file on your Garmin and simply change all dates (find & replace) to day before or after and import it again
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Old 09-22-14, 04:29 PM
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Originally Posted by RoboCheme View Post
You're welcome. I don't sprint, but here are the numbers for the first 15 seconds. The first number is the PT.

2 sec - 413, 350
3 sec - 391, 348
4 sec - 380, 338
5 sec - 364, 334
10 sec - 316, 313
15 sec - 281, 278
Well do some sprints and get back to us. Double those numbers at least.
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Old 09-22-14, 05:01 PM
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Originally Posted by popeye View Post
Well do some sprints and get back to us. Double those numbers at least.
why? I don't even like Cavendish.
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Old 09-22-14, 05:19 PM
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Originally Posted by RoboCheme View Post
why? I don't even like Cavendish.
How can we compare the two devices if all we have are some pitiful numbers? Not a slam on your fitness.
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Old 09-22-14, 05:25 PM
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Originally Posted by popeye View Post
How can we compare the two devices if all we have are some pitiful numbers? Not a slam on your fitness.
Sorry, as is typical of this forum, not one bit of gratitude and the eventual slamming (how is calling someone's wattage numbers "pitiful" not slamming?)

Go do your own testing.
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Old 09-22-14, 05:41 PM
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I will add one small advantage to the use of the PT over the crank based power meters... You can use Q-Rings and O-symmetric chain rings without bad data. AFAIK only the ROTOR PM works correctly with Q-rings.
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Old 09-22-14, 05:52 PM
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Stages Power Meter In-Depth Review Update | DC Rainmaker

I suggest you read the section on "Methodology" before making further comparisons....
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Old 09-22-14, 06:01 PM
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Originally Posted by RoboCheme View Post
Sorry, as is typical of this forum, not one bit of gratitude and the eventual slamming (how is calling someone's wattage numbers "pitiful" not slamming?)

Go do your own testing.
I'm sorry you took it that way. The numbers you posted are fine for your typical ride but you can't judge the meters if all you have are < 500 watts.
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Old 09-22-14, 06:10 PM
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Originally Posted by RoboCheme View Post
I was just interested in verifying that the Stages was in the ballpark. Given the data, I think that it was more than acceptable. Whether the PT is the right no. or the Stages is the right no., in my mind is irrelevant. I just wanted to assure myself that I can compare the Stages results to the past PT results and see how they decline with my advanced age. If you care about the absolute no. being right, probably a SRM or a Quarq is the way to go.


Iron Horse, here's my Strava ride. It shows the Stages output. Add one to three watts for the PT output.

Bike Ride Profile | PM Test II - Stages vs PT near Walnut Creek | Times and Records | Strava
+1 Interesting comparison. And nice to see in your test that the numbers were close. As you say, it doesn’t tell you which is right or wrong. It just gives you two power plots.

I've been riding with the Stages PM for a little over a month and I'm beginning to appreciate training with power vs HR. With the cost of the Stages and ease of installation, it made it an easy choice.
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Old 09-22-14, 06:11 PM
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Originally Posted by popeye View Post
I'm sorry you took it that way. The numbers you posted are fine for your typical ride but you can't judge the meters if all you have are < 500 watts.
Huh. They should read correctly regardless of input magnitude.
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Old 09-22-14, 06:20 PM
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Originally Posted by delcrossv View Post
Huh. They should read correctly regardless of input magnitude.
Well sure, they should. But I am sure some people would like some evidence that they do.

It is also possible that a person's legs might vary left to right more at a higher out put level. Actually, I think that would be probable.
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Old 09-22-14, 06:55 PM
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Originally Posted by achoo View Post
Why? Power readings are irrelevant when you're doing that type of training.
First, I disagree with your statement, but: have you no sense of intellectual curiosity?

Originally Posted by canam73 View Post
Well sure, they should. But I am sure some people would like some evidence that they do.

It is also possible that a person's legs might vary left to right more at a higher out put level. Actually, I think that would be probable.
Bingo, it would just be interesting to see some smaller time interval numbers to see how the meters diverge.
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Old 09-22-14, 07:09 PM
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Originally Posted by robabeatle View Post
First, I disagree with your statement, but: have you no sense of intellectual curiosity?



Bingo, it would just be interesting to see some smaller time interval numbers to see how the meters diverge.
I personally only think it would be an issue if somebody didn't think they could be honest in not favoring their left leg.

Otherwise, as long as the numbers are consistent from workout to workout, it should change how you train. Just don't compare numbers with a PT user.
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Old 09-22-14, 07:16 PM
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^Agree on most of this. I was considering the Stages, but I realized that on some of my long intervals for HC TTs, if I read 10 W higher over a 80 min climb, I guess I take that to heart to some degree even though the PT has a margin of error that makes that suspect. I think the Stages still has a larger margin of error, especially when considering lower cadences/changing cadence. So, I guess I am even suspect of Stages consistency...I have read the reviews.

As for sprints, I think that accuracy can be useful in assessing whether or not an anaerobic program is working or not. Here I think the Stages is very suspect. If I am a sprinter and want to see if my explosive lifting program is netting me gains this year, I'd like to see my peak numbers and compare to last year. Or maybe compare my seated high rpm sprint versus standing low rpm..Again, this may just be a consistency issue...
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