# Stages power meter reporting lower than expected wattage



## aclinjury

I have both the Powertap G3 and Stages. Friend of mine also has a Stages, and before this he also had a Powertap (but he no longer has his Powertap).

anyway, we both tested our Stages power meters against my Powertap G3, and both Stages meters (his and mine) report about 11% - 13% lower in wattage (normalized power) reading than my Powertap G3. And although he no longer has his old Powertap, he also acknowledged that the reading of the Stages is lower than his old Powertap.

Even though the numbers between the Powertap and Stages are different, but the Stage is still consistent (precise). Precision of the Stages (as shown by its graphs) mirror the precision of the Powertap. Still, it does bother me that the accuracy between the Stages and Powertap can be at 11% - 13%.

Does anyone who has a Stage can verify this observation when compared to other power meters I'm most definitely curious.


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## Srode

I would have to put both on one bike to compare heads up which I have not done. I can say on my typical rides everything I have seen indicates they are pretty close, not 11-13% apart - that's huge. My basis for saying about the same is average power over 1-2 hour rides same course similar rides and also max efforts up some longer climbs like 7-10 minute 4-5% grades.


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## Wookiebiker

I have a Stages on my Commuter bike and Powertap on my Road bike and overall, the Stages shows a bit lower power but not at the levels you are talking about ... more like 2% - 3%.

With that said ... my power imbalance can be chalked up to leg strength imbalance.

The big question is whether it's consistent with it's readings? If it's consistent, you can still use it for accurate training because you can set up your training zones with it and get the same basic feedback as you get from your Powertap. The only difference is your zones will be a little different from one meter to the other.

There are no accuracy standards for power meters at this point ... so, though they can post accuracy numbers ... what's the baseline measuring tool they are using? Until standards are set up and accepted by all power meter manufacturers there will be variances between brands ... but again, as long as they are consistent, they are a usable tool.


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## aclinjury

I've had the Powertap and Stages for awhile now, but never actually compare them, figuring that the two should be close. But the my buddy said that his Stages reads way lower wattage than his Powertap (which he had sold) and so we decided to test both our Stages against my Powertap G3.

- We tested on the same bikes
- we used 2 Garmin 500 headunits (with the lastest Garmin firmware)
- then we used a Garmin 500 and a Garmin 510 headunits (with the 500 connected to Powertap, 510 connected to Stages)
- we calibrated the power meters

And we came away with very similar results, that both our Stages is 11% - 13% below the Powertap. So our test verified my buddy's initial suspicion that prompted us to do this whole Stages vs Powertap comparison thing.

Very unlikely that both our left legs weaker than the right.

While the power chart of the Stages is consistent and it's precise, and still can serve as a training tool, but because the power discrepancy is off too much, it makes training based on %FTP using both power meters to be difficult. I mean 13% off is huge, and it messes up your %FTP target.

Also, when you're riding with another person and you're trying to match his speed on the climb and he gives you his W/kg, you're trying to train to match his W/kg. Well if the Stages is off too much, then your goal of W/kg is gonna be off too if you use the Stages.

There may be no power meter standard, but this discrepancy is too much. Something is not right here. True that precision is more important than accuracy when you only have ONE power meter to work with. But when you're training using multiple power meters, then accuracy has to be at least close within 1% - 2%, or else you're having to guess how much %FTP should you be pumping out.


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## rchung

Wookiebiker said:


> There are no accuracy standards for power meters at this point ... so, though they can post accuracy numbers ... what's the baseline measuring tool they are using?


Most manufacturers use some variation of known force and known speed as their baseline measuring tool. You can do the same thing to determine how accurate your power meter is. The easiest way is to do a static torque check. A 10% difference in power is pretty large so that should be easily detectable. You can also do a dynamic power check, though it's more hassle. Basically, you find a steep hill of known length and elevation gain, then you weigh yourself on an accurate bathroom scale while holding your bike with everything on it and wearing what you're going to be wearing for the test. Then you climb the hill at least twice (possibly more depending on your boredom threshold), once slowly at low power and once as quick as you can at high power. You want a steepish hill so that your overall speed is low enough that aerodynamic drag doesn't much matter even during your high power run. If you weighed yourself accurately and you know the elevation change accurately you can check the accuracy of your power meter(s). There are more details but that's essentially it.


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## aclinjury

rchung said:


> Most manufacturers use some variation of known force and known speed as their baseline measuring tool. You can do the same thing to determine how accurate your power meter is. The easiest way is to do a static torque check. A 10% difference in power is pretty large so that should be easily detectable. You can also do a dynamic power check, though it's more hassle. Basically, you find a steep hill of known length and elevation gain, then you weigh yourself on an accurate bathroom scale while holding your bike with everything on it and wearing what you're going to be wearing for the test. Then you climb the hill at least twice (possibly more depending on your boredom threshold), once slowly at low power and once as quick as you can at high power. You want a steepish hill so that your overall speed is low enough that aerodynamic drag doesn't much matter even during your high power run. If you weighed yourself accurately and you know the elevation change accurately you can check the accuracy of your power meter(s). There are more details but that's essentially it.


I think in theory you're right. But I think if I'm having to try to determine power via your method, it's a whole 'nother can of worm!


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## Jay Strongbow

aclinjury said:


> Very unlikely that both our left legs weaker than the right.


Actually it's very likely.


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## rchung

aclinjury said:


> I think in theory you're right. But I think if I'm having to try to determine power via your method, it's a whole 'nother can of worm!


Not really all that hard. Just pop both data sets into Golden Cheetah and look at the "Aerolab" tab. Enter your all-inclusive weight, and if the hill was steep enough all you need is a ballpark estimate of CdA -- the elevation gain won't be very sensitive to your CdA estimate very much. You have Garmin head units so you'll have the altimeter profile to check against. You did two runs (one low power - low speed, the other higher power - higher speed) so both profiles should match the altimeter, which will help you zero in on the right ballpark of Crr and CdA. If the PT is right and the Stages is reading low, the Stages elevation profile will end up too low; if the PT is reading high and the Stages is reading right, the PT profile will be too high.


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## aclinjury

Jay Strongbow said:


> Actually it's very likely.


The left may be weaker at maximal power, but not at pedestrian power of say 100W - 150W where top end power is not the limiting factor.


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## den bakker

aclinjury said:


> The left may be weaker at maximal power, but not at pedestrian power of say 100W - 150W where top end power is not the limiting factor.


how did you measure it? 
(since you say it's not the case you have measured it. right?)


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## vetboy

I think Mr Chung has basically said as much - perhaps in a roundabout way - but are you confident your PT is calibrated (I don't mean zeroed, I mean calibrated)? Have you done a static torque test? Perhaps the PT is reading 10% high?


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## aclinjury

den bakker said:


> how did you measure it?
> (since you say it's not the case you have measured it. right?)


that's correct I couldn't have measured an accurate number since at this point I'm not totally 100% sure which power meter is the errant one.

However, I can use perceived effort. After a 1-minute hard interval, I'm in total recovery mode, spinning an easy gear at an easy 85 rpm, with pedal strokes in good harmony (I'm in recovery mode). So I'm not putting out anywhere close to maximal effort. Yet the discrepancy between the Stages and PT is present and consistent. So this sort of rules out that theory that the discrepancy arises due to one leg putting out more power than the other.


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## bneudigate

I'm having the exact same issue. Two different G3's, stages, riders and head units (units set identical) and we both get the same results. Basically shows off by 20-30 watts regardless of power output between devices.


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## aclinjury

vetboy said:


> I think Mr Chung has basically said as much - perhaps in a roundabout way - but are you confident your PT is calibrated (I don't mean zeroed, I mean calibrated)? Have you done a static torque test? Perhaps the PT is reading 10% high?


PT is zeroed by removing the battery (per Powertap tech), reinsert the battery, and then letting the Garmin head unit calibrate it. That is about as much as an end user can do as far as calibrating/zeroing the PT. If the strain gauges of the PT are somewho messed up, then I guess that's something end user can't fix.


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## aclinjury

rchung said:


> Not really all that hard. Just pop both data sets into Golden Cheetah and look at the "Aerolab" tab. Enter your all-inclusive weight, and if the hill was steep enough all you need is a ballpark estimate of CdA -- the elevation gain won't be very sensitive to your CdA estimate very much. You have Garmin head units so you'll have the altimeter profile to check against. You did two runs (one low power - low speed, the other higher power - higher speed) so both profiles should match the altimeter, which will help you zero in on the right ballpark of Crr and CdA. If the PT is right and the Stages is reading low, the Stages elevation profile will end up too low; if the PT is reading high and the Stages is reading right, the PT profile will be too high.


I might have to try this then


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## aclinjury

I'm in the process of testing my Powertap against an a couple buddies' different brand power meters. So I'm hoping to get to the bottom of this soon.


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## vetboy

aclinjury said:


> PT is zeroed by removing the battery (per Powertap tech), reinsert the battery, and then letting the Garmin head unit calibrate it. That is about as much as an end user can do as far as calibrating/zeroing the PT. If the strain gauges of the PT are somewho messed up, then I guess that's something end user can't fix.


Exactly. Point being, you powertap could just as easily be the issue as the Stages. In fact, you have two Stages meters agreeing and one PT that does not. Kinda makes you want to look into the PT before concluding that two Stages are reading low.

And can you not do a static torque test on a PT? Don't own one so I'm not that familiar with them.


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## bneudigate

aclinjury said:


> I'm in the process of testing my Powertap against an a couple buddies' different brand power meters. So I'm hoping to get to the bottom of this soon.


Keep me posted


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## MMsRepBike

rchung said:


> Not really all that hard. Just pop both data sets into Golden Cheetah and look at the "Aerolab" tab. Enter your all-inclusive weight, and if the hill was steep enough all you need is a ballpark estimate of CdA -- the elevation gain won't be very sensitive to your CdA estimate very much. You have Garmin head units so you'll have the altimeter profile to check against. You did two runs (one low power - low speed, the other higher power - higher speed) so both profiles should match the altimeter, which will help you zero in on the right ballpark of Crr and CdA. If the PT is right and the Stages is reading low, the Stages elevation profile will end up too low; if the PT is reading high and the Stages is reading right, the PT profile will be too high.


nice advice here.


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## rchung

vetboy said:


> And can you not do a static torque test on a PT? Don't own one so I'm not that familiar with them.


You can, and the procedure is pretty simple though the buttons you push depend exactly on which model of Garmin (or other head unit) you use. There are some detailed instructions for one protocol here.


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## deviousalex

aclinjury said:


> If the strain gauges of the PT are somewho messed up, then I guess that's something end user can't fix.


I think I had that issue but it was easy to detect. It said I was doing 900 watts when soft pedaling.

Stages Power Meter In-Depth Review Update | DC Rainmaker

Some interesting data in this updated review of the stages.


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## carlosflanders

aclinjury said:


> The left may be weaker at maximal power, but not at pedestrian power of say 100W - 150W where top end power is not the limiting factor.


Actually, it's the opposite.


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## MMsRepBike

deviousalex said:


> I think I had that issue but it was easy to detect. It said I was doing 900 watts when soft pedaling.
> 
> Stages Power Meter In-Depth Review Update | DC Rainmaker
> 
> Some interesting data in this updated review of the stages.


I can't stand that guy. He comes off to me as such an arrogant prick. That being said you are correct, the data is interesting and telling. Currently I don't think anyone has any merit to say there is a "best" power meter or "most accurate" one on the market. It's more just a differentiation on form factor now. There's hubs, spiders, non-drive crank arms, pedals, crank arms + pods, lots of form factor options.

As for the topic at hand, interested to see which one shows to be reading off. Seems that the PT is the culprit seeing how the Stages is reading just like the other Stages.


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## Srode

Stages has an iOS app you can download which let's you do static torque testing I thought?


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## deviousalex

MMsRepBike said:


> I can't stand that guy. He comes off to me as such an arrogant prick.


His reviews are thorough though.

@OP - Is the firmware up to date?


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## den bakker

aclinjury said:


> that's correct I couldn't have measured an accurate number since at this point I'm not totally 100% sure which power meter is the errant one.
> 
> However, I can use perceived effort. After a 1-minute hard interval, I'm in total recovery mode, spinning an easy gear at an easy 85 rpm, with pedal strokes in good harmony (I'm in recovery mode). So I'm not putting out anywhere close to maximal effort. Yet the discrepancy between the Stages and PT is present and consistent. So this sort of rules out that theory that the discrepancy arises due to one leg putting out more power than the other.


im not sure how you get to the conclusion your power output is symmetric at any effort. Almost everybody is asymmetric


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## mikerp

MMsRepBike said:


> As for the topic at hand, interested to see which one shows to be reading off. Seems that the PT is the culprit seeing how the Stages is reading just like the other Stages.


So your logic is if 2 like brands units read the same, and another brand reads differently it must be flawed? 
BTW you missed this from the OP
"And although he no longer has his old Powertap, he also acknowledged that the reading of the Stages is lower than his old Powertap."
So it's a 2 vs. 2 not 2 vs. 1


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## looigi

MMsRepBike said:


> I can't stand that guy. He comes off to me as such an arrogant prick. ....


Interesting. I don't get that impression at all. His reviews seem very thorough, straightforward and objective. When he gives his opinions he identifies them as such, and he also admits to the limits of his knowledge and understanding and doesn't extrapolate beyond them.


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## aclinjury

Srode said:


> Stages has an iOS app you can download which let's you do static torque testing I thought?


I did that with the apps, and the results were the same


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## aclinjury

den bakker said:


> im not sure how you get to the conclusion your power output is symmetric at any effort. Almost everybody is asymmetric


I know it's asymmetric. But over 10% asymmetric? Maybe if it were 3-4% asymetric I can accept it was my leg.


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## aclinjury

mikerp said:


> So your logic is if 2 like brands units read the same, and another brand reads differently it must be flawed?
> BTW you missed this from the OP
> "And although he no longer has his old Powertap, he also acknowledged that the reading of the Stages is lower than his old Powertap."
> So it's a 2 vs. 2 not 2 vs. 1


That's correct. 2 vs 2.


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## aclinjury

deviousalex said:


> I think I had that issue but it was easy to detect. It said I was doing 900 watts when soft pedaling.
> 
> Stages Power Meter In-Depth Review Update | DC Rainmaker
> 
> Some interesting data in this updated review of the stages.


When I calibrate the PT using the Garmin 500 headunit, the Garmin displays a torque value of .12 initially but then shows torque as 0 once the calibration is complete. The "calibration value" (the second number on the Garmin) eventually shows 514. The PT tech once told me that 514 is perfectly normal. So as far as I can tell, the PT is calibrated correctly.


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## aclinjury

by this weekend I'm hoping to test my PT (and hopefully the Stages too) against an SRM and a Quarq. So hopefully I'll to the bottom of this soon. It'll be interesting testing all these power meters in one session.


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## deviousalex

aclinjury said:


> I know it's asymmetric. But over 10% asymmetric? Maybe if it were 3-4% asymetric I can accept it was my leg.


I saw a graph once (don't remember hwere) that plotted the power difference in legs across multiple RPMs. Just because it's 3-4% at 150 watts/80 rpm doens't mean it's the same at 500 watts at 95rpm.


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## vetboy

aclinjury said:


> When I calibrate the PT using the Garmin 500 headunit, the Garmin displays a torque value of .12 initially but then shows torque as 0 once the calibration is complete. The "calibration value" (the second number on the Garmin) eventually shows 514. The PT tech once told me that 514 is perfectly normal. So as far as I can tell, the PT is calibrated correctly.


I don't think you can draw that conclusion without a static torque test. Basically, you need to hang a known weight from the crankarm and ensure that the resulting torque is correct. It's not quite that simple - I'm skipping some details - but it's not hard either. If you search around the interwebs, you'll find a more detailed explanation. Basically, wout a static torque test, you cannot conclude that your PT is reading correct. All you did above is zero the unit, which is different from calibration.


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## mikerp

aclinjury said:


> When I calibrate the PT using the Garmin 500 headunit, the Garmin displays a torque value of .12 initially but then shows torque as 0 once the calibration is complete. The "calibration value" (the second number on the Garmin) eventually shows 514. The PT tech once told me that 514 is perfectly normal. So as far as I can tell, the PT is calibrated correctly.


514 is a good number for a PT. When they fail they fail and you will have a number outside of the allowable spread for the units.


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## bneudigate

deviousalex said:


> I think I had that issue but it was easy to detect. It said I was doing 900 watts when soft pedaling.
> 
> Stages Power Meter In-Depth Review Update | DC Rainmaker
> 
> Some interesting data in this updated review of the stages.


I think I read every review prior to finally making the decision to purchase a stages. That's why it's puzzling that this meter is so far off. It could be the powertap, we will find out soon enough. I had a lengthy conversation with SRM about all of this yesterday and decided to purchase one. You are going to be hard pressed to find anyone credible that's going to say the SRM is wrong.


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## rchung

bneudigate said:


> You are going to be hard pressed to find anyone credible that's going to say the SRM is wrong.


Every power meter, including the SRM, can be mis-calibrated (rare), or incorrectly zeroed (pretty common). Trust but verify -- especially since verification usually isn't very hard to do.


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## MMsRepBike

bneudigate said:


> I think I read every review prior to finally making the decision to purchase a stages. That's why it's puzzling that this meter is so far off. It could be the powertap, we will find out soon enough. I had a lengthy conversation with SRM about all of this yesterday and decided to purchase one. You are going to be hard pressed to find anyone credible that's going to say the SRM is wrong.


just wow.


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## aclinjury

vetboy said:


> I don't think you can draw that conclusion without a static torque test. Basically, you need to hang a known weight from the crankarm and ensure that the resulting torque is correct. It's not quite that simple - I'm skipping some details - but it's not hard either. If you search around the interwebs, you'll find a more detailed explanation. Basically, wout a static torque test, you cannot conclude that your PT is reading correct. All you did above is zero the unit, which is different from calibration.


I'm waiting for to test my PT against a couple buddies' SRM and Quarq, and if my PT agrees with the SRM and Quarq more than it agrees with the Stages, then I'm going to conclude that the Stages is off.

At this point I'm not going to do the test you said above. Reason is I'm not experienced in testing these things, I may introduce more errors and raising more questions than answers. I mean the experts test these things in a lab using highly specialized equipment and experience. I'm pretty sure I'd get the test wrong.


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## bneudigate

rchung said:


> Every power meter, including the SRM, can be mis-calibrated (rare), or incorrectly zeroed (pretty common). Trust but verify -- especially since verification usually isn't very hard to do.


Not right out of the factory. Call SRM they will explain this to you.


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## rchung

bneudigate said:


> Not right out of the factory. Call SRM they will explain this to you.


I've been doing this for a while. I've seen one SRM that was off directly from the factory and one whose calibration slipped over the first few weeks before stabilizing. Trust but verify -- especially since verification isn't hard to do.


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## deviousalex

rchung said:


> I've been doing this for a while. I've seen one SRM that was off directly from the factory and one whose calibration slipped over the first few weeks before stabilizing. Trust but verify -- especially since verification isn't hard to do.


How did you know it slipped? If it starts giving you numbers like 300 watts when soft pedaling it's easy to spot but a 10-15 watt difference will not be easy to spot.


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## rchung

deviousalex said:


> How did you know it slipped? If it starts giving you numbers like 300 watts when soft pedaling it's easy to spot but a 10-15 watt difference will not be easy to spot.


I get asked to check my friends' and acquaintances' power meters cuz they know I know how to do it. In that case, we checked the calibration because he had just purchased a second SRM. Over the course of a few weeks he thought that the new SRM began reading off, so we checked it again and found out that its calibration had changed. This was part of the (infamous) batch of SRMs from the early 2000's when SRM had changed their epoxy supplier. As I said, I've been doing this for a while.


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## r1lee

aclinjury said:


> I'm waiting for to test my PT against a couple buddies' SRM and Quarq, and if my PT agrees with the SRM and Quarq more than it agrees with the Stages, then I'm going to conclude that the Stages is off.


what if the SRM or Quarq comes in at 5-6% above the Stages? Which would then make the same below the PT?

I also have a PT G3 and picking up my bike from the shop later tomorrow which will have the Stages. 

I'm going to test this out.


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## thumper8888

My stages is consistently about 10-12 watts higher than my 2014 Red quarq.
I dont know that one feels more accurate than the other. But theyre both consistent, and that's what counts.

if I had to guess, the reason is left-leg dominance. traditionally I have been right-legged in sports. Knee injury though has left left at lest looking more developed


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## Alex_Simmons/RST

A few comments.

1. Asymmetry of left-right power output is normal and it varies between individuals and for an individual due to various things. Many (but not all) become more symmetrical as they approach threshold power levels. 

A 10% variance between Stages and a spider based power meter is totally plausible, especially when pedalling at low wattages. 

For a start, a 45:55 left:right balance (or 55:45) at very low power is not uncommon.

Keep in mind that if you are actually 45%:55% left:right at a low wattage (e.g. 100W), then the Stages will report power as 2 x 45W = 90W, while your actual two leg power is 100W. 

There's a 10% difference right there and that assumes both meters are equally accurate in measuring what they measure.


2. For a Powertap, you need to have several things checked to have confidence:

a. That you have checked and set the torque zero (which Garmin mislabel as "calibration"), AND

b. the torque zero is within specification (e.g. 512 +/- ~ 10 or so units), AND

c. that the torque zero does not fluctuate when no torque is being applied (if you see the numbers bounce about then you have a problem), AND

d. that the "slope" of the power meter is correct. IOW it's not enough to know the meter reports zero torque when there is no torque applied. You also need to verify that it correctly reports torque when a known torque is applied. It's this latter step that verifies a power meter's calibration.

I use the bathroom scale analogy. The bathroom scales might read zero when you are not standing on them, but that does not mean they will be accurate when you do stand on them. You also need to verify they correctly read a known weight.

e. while not an absolute necessity, it is also a good idea when validating the slope calibration of a Powertap to check its behaviour in different gear combinations.


While it's possible to verify the slope calibration of a Powertap (and most power meters), not all power meters permit you to adjust that slope calibration if you find it is incorrect. Powertap, Stages, Power2Max don't allow the user to adjust this calibration. SRM and Quarq do.


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## rchung

Alex_Simmons/RST said:


> A few comments.
> 
> 1. Asymmetry of left-right power output is normal and it varies between individuals and for an individual due to various things. Many (but not all) become more symmetrical as they approach threshold power levels.


I'm thinking even if you become more symmetrical as you approach threshold the Stages still probably isn't the right power meter for you. 

You got any clients who use the Stages yet?


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## vetboy

bneudigate said:


> Not right out of the factory. Call SRM they will explain this to you.





deviousalex said:


> How did you know it slipped? If it starts giving you numbers like 300 watts when soft pedaling it's easy to spot but a 10-15 watt difference will not be easy to spot.


Careful guys. Calling out Mr Chung on his power meter prowess is a little like trying to argue Newton's laws with your college physics professor - the only one coming away looking stupid is you


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## Alex_Simmons/RST

rchung said:


> I'm thinking even if you become more symmetrical as you approach threshold the Stages still probably isn't the right power meter for you.
> 
> You got any clients who use the Stages yet?


No. One was going to but ended up on sponsored Vectors instead. All the rest are on PTs, SRMs, Quarqs or Vectors. No P2Ms in my lot either yet.


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## rchung

Speaking of checking the PT on different cogs of the cassette (and I agree with that) do you check both the outer and inner chain rings when testing a spider-based PM? 

I remember that years ago Tobin used to hang the weight not from the pedal spindle but from a piece of chain hung over the chain rings. That's how he discovered that his SRM gave different readings "around the clock."


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## deviousalex

vetboy said:


> Careful guys. Calling out Mr Chung on his power meter prowess is a little like trying to argue Newton's laws with your college physics professor - the only one coming away looking stupid is you


How is this "calling out" anyone? I was asking a legitimate question.


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## rchung

FWIW, I didn't take your question as "calling out" -- I took it as a real question. However, vetboy has probably seen an instance or two in the past when people have done so.


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## Fireform

And yet no head to head reviews I've seen show more than a few percent difference at most between stages and any other meter. My powertap and stages results are so close I quit bothering to compare them.


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## rchung

Fireform said:


> And yet no head to head reviews I've seen show more than a few percent difference at most between stages and any other meter. My powertap and stages results are so close I quit bothering to compare them.


What's important isn't how close two power meters are on average. What's important is knowing when they're not.


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## Fireform

From what I can see, the noise in the ant+ data transmission is at least as great as the differences among any of the direct force meters.


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## vetboy

deviousalex said:


> How is this "calling out" anyone? I was asking a legitimate question.


Don't be too offended. It was mostly intended as a fun comment to point out that rchung probably has as much (or more) PM knowledge as anyone here on RBR.


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## rchung

Fireform said:


> From what I can see, the noise in the ant+ data transmission is at least as great as the differences among any of the direct force meters.


I haven't found that to be the case. I agree that the noise can be high but it's still possible to extract signal. Sometimes ferreting out the signal is a little harder, sometimes it's a little easier but, thus far, I don't think the ANT+ protocol has been the problem.


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## looigi

ANT+ is digital, so assuming the protocol is properly designed the transmission/reception is noiseless. The analog signals from the strain gauges and subsequent ADC will have noise, but there should be no additional noise after that.


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## deviousalex

looigi said:


> ANT+ is digital, so assuming the protocol is properly designed the transmission/reception is noiseless. The analog signals from the strain gauges and subsequent ADC will have noise, but there should be no additional noise after that.


Right, in worst case you just won't get any data. When I ride by these radio towers around here the power meter temporarily displays -- on my Garmin.


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## Fireform

In one of Rainmaker's reviews he shows records of data from the same power meter (an SRM IIRC) and same ride recorded simultaneously on different head units that differed more from each other than most of the different meters varied from one another. That's very telling. It's not noise exactly, but digital artifacts that are very significant.


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## rchung

Fireform said:


> In one of Rainmaker's reviews he shows records of data from the same power meter (an SRM IIRC) and same ride recorded simultaneously on different head units that differed more from each other than most of the different meters varied from one another. That's very telling. It's not noise exactly, but digital artifacts that are very significant.


I don't remember that but Greg Kopecky from Slowtwitch did a similar test with different head units recording from the same device. In part, I think that's more about the head unit than the ANT+ protocol -- ANT+ requires transmission at 4Hz but most head units record at 1Hz so part of the issue is which of the packets gets dropped. Ray now uses a Wasp to collect all the data from each PM so we were able to get around that. It's clear that certain head units "lag" a bit, especially when starting and stopping but there are ways to handle that. It's actually an easier problem to deal with than the problem of synching up 1Hz head units with the old 1.26-second PT head units, or dealing with the "virtual" cadence from PTs. If more power meters were reporting at higher Hz then maybe ANT+ would be the bottleneck but right now I don't think it is.


----------



## aclinjury

r1lee said:


> what if the SRM or Quarq comes in at 5-6% above the Stages? Which would then make the same below the PT?
> 
> I also have a PT G3 and picking up my bike from the shop later tomorrow which will have the Stages.
> 
> I'm going to test this out.


Please post your results. I'm very interested in knowing.

If you could test both PM's at the same time (you'd need 2 headunits), that would be best.


----------



## aclinjury

I've been busy with either riding or working, so haven't had time to deal with this at the moment. 

But I like rchung's ideas of verifying using a short steep hill.

The only 2 reviews I read of the Stages is the one from DC Rainmakers and the DurianRider guy, and they both showed good reviews.

I need to do some further testing and verfication this weekend!

I wonder if Stages might have made a bad batch? From what I gather, Stages has a huge backlog and is rushing, running 2 shifts at their factory, to get these things out. I really wonder if me and my buddy got a bad batch since we both seem to get them around the same time.


----------



## aclinjury

Alex_Simmons/RST said:


> A few comments.
> 
> 1. Asymmetry of left-right power output is normal and it varies between individuals and for an individual due to various things. Many (but not all) become more symmetrical as they approach threshold power levels.
> 
> A 10% variance between Stages and a spider based power meter is totally plausible, especially when pedalling at low wattages.
> 
> For a start, a 45:55 left:right balance (or 55:45) at very low power is not uncommon.
> 
> Keep in mind that if you are actually 45%:55% left:right at a low wattage (e.g. 100W), then the Stages will report power as 2 x 45W = 90W, while your actual two leg power is 100W.
> 
> There's a 10% difference right there and that assumes both meters are equally accurate in measuring what they measure.
> 
> 
> 2. For a Powertap, you need to have several things checked to have confidence:
> 
> a. That you have checked and set the torque zero (which Garmin mislabel as "calibration"), AND
> 
> b. the torque zero is within specification (e.g. 512 +/- ~ 10 or so units), AND
> 
> c. that the torque zero does not fluctuate when no torque is being applied (if you see the numbers bounce about then you have a problem), AND
> 
> d. that the "slope" of the power meter is correct. IOW it's not enough to know the meter reports zero torque when there is no torque applied. You also need to verify that it correctly reports torque when a known torque is applied. It's this latter step that verifies a power meter's calibration.
> 
> I use the bathroom scale analogy. The bathroom scales might read zero when you are not standing on them, but that does not mean they will be accurate when you do stand on them. You also need to verify they correctly read a known weight.
> 
> e. while not an absolute necessity, it is also a good idea when validating the slope calibration of a Powertap to check its behaviour in different gear combinations.
> 
> 
> While it's possible to verify the slope calibration of a Powertap (and most power meters), not all power meters permit you to adjust that slope calibration if you find it is incorrect. Powertap, Stages, Power2Max don't allow the user to adjust this calibration. SRM and Quarq do.


thank you for the tips!

(PS: always enjoy reading your comments due to their details).


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## mikerp

vetboy said:


> Don't be too offended. It was mostly intended as a fun comment to point out that rchung probably has as much (or more) PM knowledge as anyone here on RBR.


I'm pretty sure Robert has more knowledge.


----------



## Alex_Simmons/RST

bneudigate said:


> Not right out of the factory. Call SRM they will explain this to you.


Over the years the reliability of the factory calibration value of SRMs has improved, IME. 

In years past I have seen variances from factory calibrations of several %. I can't say why it's the case but I think it makes sense to validate calibration after a unit has been installed on your bike. 

My experience over the last few years (I guess I've calibrated a couple of dozen SRMs, as well as similar number of Quarqs and a few PTs) suggests this is less of an issue than it used to be. But as is always the case, why not check anyway and be sure?


----------



## Alex_Simmons/RST

rchung said:


> Speaking of checking the PT on different cogs of the cassette (and I agree with that) do you check both the outer and inner chain rings when testing a spider-based PM?
> 
> I remember that years ago Tobin used to hang the weight not from the pedal spindle but from a piece of chain hung over the chain rings. That's how he discovered that his SRM gave different readings "around the clock."


Typically I'll check both chainrings. Don't see many triple SRMs. Have tested MTB triple with Powertap.

I have one of tested my own units around the clock (partially), which you can do by clamping the bike in a bike trainer, and then rotate the bike around the rear axle, e.g. lift front wheel up onto a chair to get near 45 degrees, or vertically against a wall to get ~90 degrees, and even flipped right over on the bike's back. Obviously not the whole 360 degrees but enough to make a quick check and see if there are any anomalies over 180 degrees. Mine was consistent so I didn't bother again. 

Given peak torque is either side of ~ 3 o'clock, then I figure that's where you'd want the least error if there are any variances around the clock, and that's what you check when bike is in normal position (although some do lift front wheel to give enough floor clearance to hang weights).


----------



## r1lee

aclinjury said:


> Please post your results. I'm very interested in knowing.
> 
> If you could test both PM's at the same time (you'd need 2 headunits), that would be best.


Got to figure out where to get the second head unit. But will let you know.


----------



## Srode

rchung said:


> What's important isn't how close two power meters are on average. What's important is knowing when they're not.


That makes good sense. However the reviews I have read show that using somewhat averaged (3 second moving averages which IMHO is the most useful during the ride data for power) not overall averages, the stages PM followed the others quite closely. Bigger variances showed up when the other PMs needed to temperature compensate in the DC Rainmaker review, and returned to matching closely after they were reset for temperature. 20% off for stages is very inconsistent with any review I have seen. My only complaint comparing it to my PT wheel is it takes too long to start reporting after I start moving. 

If I was getting results that far off vs the other PMs, I would be contacting Stages for evaluation / recalibration / remedy. Doesn't sound like it's a Stages design issue rather a problem with a specific unit to me.


----------



## rchung

Srode said:


> That makes good sense. However the reviews I have read show that using somewhat averaged (3 second moving averages which IMHO is the most useful during the ride data for power) not overall averages, the stages PM followed the others quite closely. Bigger variances showed up when the other PMs needed to temperature compensate in the DC Rainmaker review, and returned to matching closely after they were reset for temperature.


Everyone points to the temperature compensation as an area where the Stages does well compared to Ray's PT and Quarq but many people seem to miss the overall lesson of that review. Recall that in the initial review we did I had identified not only the temperature problem but also that the Stages did okay on smooth surfaces and at "usual" power output but poorly at low cadence and on bumpy surfaces (Stages later released a firmware update to address the bumpy surface problem and now has clarified an "operating range" for cadence). That's what I meant about what's important isn't so much how they compare on average but understanding where they're different. 

Here's a plot from Ray's later ride with the PT, the Quarq, the Stages, and the Vector. What this shows is that for that particular ride on that particular day there was a relatively large difference between the Stages and the other three PMs at high power, but a relatively small difference over longer durations near FTP. 









What does this mean? I think what it means is that if you spend most of your time in the "middle" of the power range and you don't much care about the "ends" of the range (that is, high or low power, or maybe high and low force and cadence), or you spend most of your time in situations without huge swings in temperature during the course of your ride, and you mostly use a power meter for tracking TSS or maybe your FTP, then you're in luck -- any of these will do fine. However, if you're among the minority of riders (and I emphasize minority) who do, say, QA analysis, or maybe drag estimation, or maybe standing start sprints, or maybe the new FRC, or you need operate over a wide temperature range without the opportunity to trigger "automatic" re-zeroing you may want to pay attention to how wide and stable the "operating range" is. Not many riders do ramp tests (unless they have sadistic coaches (like Alex?)) but I suppose if you were in that situation, you'd want to be sure that the incremental steps were of the targeted size; lots of people say "accuracy doesn't matter, what matters is that it's consistent" but ramp tests are a situation where consistency wouldn't suffice. For that you'd need accuracy.

Anyway, that's a long way of saying that when I do these analyses and comparisons I don't just look at the average power over a ride; I try to figure out where they're different. As long as you understand where your particular power meter does well and where it does poorly, you'll probably be okay.


----------



## Srode

Interesting - the graph does show quite a bit of difference in the higher range. I apparently didn't pay close enough attention when I read the article. For me, I'm using the stages on my rain bike for TSS and pacing on climbs mostly and it does well enough for me. The PT wheel on the good bike does the rest.


----------



## spdntrxi

I have not compared my PT to stages yet, since I dont have 2 head units. I did however attempt to match my PT to the wahoo kickr and I think it's pretty close. In any event I rode my stages bike on my wahoo kickr and the stages read about 5w higher then the wahoo in erg mode. If the cadence is steady maybe even less, but if I speed up the cadence the stages will jump higher then the kickr will hold pretty steady pretty much (erg mode after all)


----------



## TehYoyo

You'll always see different power meters report different wattages. I think SRM is always highest and PowerTap usually (although clearly not in this case) lowest (SRM measures closest to source, although Garmin is probably higher now and PowerTap sufferes from drivetrain inefficiency.

Regardless, the only thing you _need_ for training is tracking consistency. If you want the real numbers for tests, just do testing w/ the PowerTap or inflate your Stages numbers by 10%.


----------



## looigi

rchung said:


> ... lots of people say "accuracy doesn't matter, what matters is that it's consistent" but ramp tests are a situation where consistency wouldn't suffice. For that you'd need accuracy...


Do you absolutely need accuracy for this or would precision and linearity suffice (assuming insensitivity to temp and rpm)?


----------



## rchung

looigi said:


> Do you absolutely need accuracy for this or would precision and linearity suffice (assuming insensitivity to temp and rpm)?


The reason why you go to the trouble to do a ramp test is because you're trying to identify an absolute quantity, like VO2Max or something similar, like power at VO2Max. For this you can't just say, "the subject failed at this step of the ramp" you actually want to be sure how "high" each step is. And, since you're testing way above LT you might be concerned that the subject will start to favor one leg if that will allow him to make the step rather than fail. Ramp tests are a protocol that demands pretty high data integrity because you're estimating something based on a maximum value rather than an average value. In statistics, estimating the extremes of a distribution is a much harder problem than estimating the mean of a distribution, and experimental or measurement error makes the problem even tougher. 

But not many people need to do ramp tests. I was just pointing them out as an example of something that requires pretty high data quality.


----------



## aclinjury

Hey folks, I still haven't found time to test the PT vs. the Stages yet, partly becaues of time issue and partly because of equipment issue.

However, over this weekend, I was able to do a long mountain ride, using the Stages. Here's are the numbers. I held a 92.4% FTP (*with FTP recently measured by a full 1-hr flatland effort using Powertap G3*) for a 2-hr climb duration. My heartrate for the duration was pretty much close to FTP heartrate. 

I was able to I PR'ed almost all Strava segments on this climb. So what I'm saying is that it was pretty much maximum effort climb for me.

Based on the wattage number reported by the Stages, based on my heartrate, based on my perceived effort, and based on my time on all the segments... I can say that there is NO way that the Stages was under-reporting wattage on this particular ride. Because if the Stages was under-reporting wattage, then that would mean that my 92% FTP effort could even be 102%+ FTP wattage for a 2 hr duration! No way I would have been able to climb at over 100% FTP for 2 hr.

And as far as displaying the wattage number on the Garmin headunit, I paid close attention to it, and to my surprise, the number track very well. Meaning, the wattage displayed did not jump anymore than my PT, and the wattage displayed pretty much showed I'm at 92% FTP most of the time.

On this ride, the Stage behaved exactly like my Powertap. There is no way the Stages could have been under reporting on this ride.

My previous tests that I mentioned above was done on the trainer, and I don't know if this would have made the Stages to behave a little differently? Also on the trainer, I did not get a chance to put out near FTP effort over a long duration (like a 2hr climb fest).

So that is all I have to report for now. I'm still awaiting to test the Stages against an SRM.


----------



## rchung

aclinjury said:


> My previous tests that I mentioned above was done on the trainer


Hmmm. You didn't say that your previous tests were on a trainer. How many comparison rides did you do, and did you re-zero both PMs before each trainer session? When you said "Stages is 10% lower" was that from one trainer ride or several? 

You know up above where I keep harping that what's important is knowing the conditions under which power meters differ? Here's one: you have to scrupulously manually re-zero PTs (and some other PMs) on trainers because there's often no coasting, and coasting is what triggers the auto-zero.


----------



## aclinjury

rchung said:


> Hmmm. You didn't say that your previous tests were on a trainer. How many comparison rides did you do, and did you re-zero both PMs before each trainer session? When you said "Stages is 10% lower" was that from one trainer ride or several?
> 
> You know up above where I keep harping that what's important is knowing the conditions under which power meters differ? Here's one: you have to scrupulously manually re-zero PTs (and some other PMs) on trainers because there's often no coasting, and coasting is what triggers the auto-zero.


The "10% lower" figure is just from a few tries on the trainer. And while I re-zeroed the PT, I don't recall if I re-zeroed it on the trainer or not. I should really keep notebook recording all exact steps I do. I think I'm gonna have to go back to the basics and test everything over again, more meticuously.

But after this long weekend climbfest, the Stages did look good, in both accuracy and precision (at least at near threshold effort), and even looked good as a pacing tool (at least pacing at near constant threshold effort). I like.

Maybe Alex was right, at threshold power, there's less power discrepancy between right and left legs, and this would explain why at threshold my numbers from the Stages look similar to the PT

so back to the drawing board on the testing at lower power and why there's more variances at lower power...


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## iclypso

Good discussion and quite a bit more technical than I expected. My first reaction was this: Powertap is the pants' size you order, Stages is the waist size you actually are. In other words, tell the customer what he wants to hear, within reason.

An interesting corollary to Rainmaker's (via Fireform's post in this thread) experiment would be to compare simultaneous data from cranks and hub. Anyone done that?


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## rchung

iclypso said:


> An interesting corollary to Rainmaker's (via Fireform's post in this thread) experiment would be to compare simultaneous data from cranks and hub. Anyone done that?


Yes. People have been doing that since the first E-Tune Power Tap was released.


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## Dunbar

iclypso said:


> Good discussion and quite a bit more technical than I expected. My first reaction was this: Powertap is the pants' size you order, Stages is the waist size you actually are. In other words, tell the customer what he wants to hear, within reason.


Maybe in the OP's case but I haven't seen a lot of evidence that Powertaps read high in general. In fact, most people who use crank and hub based PM's will tell you the crank based PM's read slightly higher (which makes sense.) There can be a fairly significant variation even amongst the exact same model of PM. And unless you test yourself on a device with regularly verified accuracy you can never know for sure just how accurate your PM is.


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## rchung

Dunbar said:


> And unless you test yourself on a device with regularly verified accuracy you can never know for sure just how accurate your PM is.


That device with regularly verified accuracy can be the scales at your local post office or UPS or FedEx center.


----------



## triwarrior

*Stages Low Power test*



aclinjury said:


> The "10% lower" figure is just from a few tries on the trainer. And while I re-zeroed the PT, I don't recall if I re-zeroed it on the trainer or not. I should really keep notebook recording all exact steps I do. I think I'm gonna have to go back to the basics and test everything over again, more meticuously.
> 
> But after this long weekend climbfest, the Stages did look good, in both accuracy and precision (at least at near threshold effort), and even looked good as a pacing tool (at least pacing at near constant threshold effort). I like.
> 
> Maybe Alex was right, at threshold power, there's less power discrepancy between right and left legs, and this would explain why at threshold my numbers from the Stages look similar to the PT
> 
> so back to the drawing board on the testing at lower power and why there's more variances at lower power...


*******
I did a comparison of my new Stages Ultegra 6700 crank arm (paired to Garmin 910XT) on Ultegra 6800 crank vs my Computrainer

Computrainer Avg Wattage/Stages Avg Wattage

May 17/14
5' intervals as:
173/176 Aero position
203/206 Aero position
245/247 Aero position
306/314 Aero position
150/150 Aero position
148/172 Sitting up entering data on phone ie. No hands on handlebars - creating more L/R imbalance?

May 22/14
Wu w CT not calibrated - CT 20W lower 
After 10' WU then CT Calibration (2.39 RC):
233/227 12' Aero
116/106 2' spin then Stages Calibration (902)
241/232 12' Aero (50/50, 70-72 spinscan) 
121/123 2' spin
243/233 12' Aero
131/121 12' Aero

May 25/14 
wu 10’ Stages calibrated, CT not calibrated
89/87
CT calibrated 
118/112

So overall, the Stages was fairly close, with one session reading above the Computrainer, and others a little lower.
My L/R balance on the CT were 51/49, 50/50 for the majority of the time.


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## bikeguy0

A another data point. I have a 45/55 power split left to right. I had a stages on the mtb and it read 10-15% lower than my quarq on road bike. In that situation it made it untenable for me. If I decide to do intervals on my mtb I need the power to be more accurate to be in the right power zone and have the IF and TSS calculate correctly. I got rid of the stages and am lookin at getting an srm for the mtb which should be much closer to the quarq on the road bike. 

Now if I had two stages it might be okay but I have trained on a quarq for 4 years so basically all the numbers from prior rides are going to be different and if I injure my knee for some reason now the stages will be even more off. For me it was not worth it, I want numbers that are accurate day to day and able to be compared to my road bike power.


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## spdntrxi

My data point : Stages vs Kickr Trainer 

I found using the wahoo app (phone app) the stages reads higher then the kickr in pretty much any mode ( I use ERG a lot).. however if I using the wahoo segments app and putting it thought the paces of a live segment the stages and kickr match very well. In erg mode sometimes the difference is 10-15w.


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## bikeguy0

I think this really comes down to if you only use a stages to train with no comparison to other devices. It does have repeatability to itself but is not as accurate as other, more expensive, equipment.

My problem really came from left only power measurement on Stages and full measurement by the Quarq. Having a 10% difference is huge. I really noticed it when I had a stages on my road bike too (forgot to mention that in previous post, this was before I had a mtb version). I went to do a LT test and I was shooting to beat my prior 20m power. I really suffered and couldn't hold the pace anymore at about 12-15 minutes. I was really frustrated and then later realized that the reason I couldn't hold the pace was because I was pushing 10% or move wattage than I thought I was. My Garmin was showing 275 watts but I actually was pushing over 300.


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## OldChipper

spdntrxi said:


> My data point : Stages vs Kickr Trainer
> 
> I found using the wahoo app (phone app) the stages reads higher then the kickr in pretty much any mode ( I use ERG a lot).. however if I using the wahoo segments app and putting it thought the paces of a live segment the stages and kickr match very well. In erg mode sometimes the difference is 10-15w.


I just found this thread when I finally got around to comparing my Stages to my Kickr and discovered that the Stages consistently reads 20-40 watts lower than the Kickr in a range from 100w - 250w (reported on the Kickr) whether I use the Wahoo Kickr app or the TrainerRoad app. The Wahoo and TR apps are running on my iPad and the Stages is paired to a Garmin 1000. 

Hopefully will have a chance to compare the Stages to a G3 over the weekend.


----------



## vs779

OldChipper said:


> I just found this thread when I finally got around to comparing my Stages to my Kickr and discovered that the Stages consistently reads 20-40 watts lower than the Kickr in a range from 100w - 250w (reported on the Kickr) whether I use the Wahoo Kickr app or the TrainerRoad app. The Wahoo and TR apps are running on my iPad and the Stages is paired to a Garmin 1000.
> 
> Hopefully will have a chance to compare the Stages to a G3 over the weekend.


I currently have a PowerSync which is same as Kickr and I find in a controlled resistance workout (250W x 5Min) my Stages avg is about 10% less. Now if I don't use the erg mode and just ride at 250W x 5min they are within 2%. I'm gonna try a Kickr and see how close the avg#'s are. BTW I did test with 2 different Stages units and got the same results.


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## raptor3x

Just to chime in, I just switched from a powertap hub (which I still have) to two separate Stages units for my TT and road bikes. The stages units are consistent with one another, but both are reading ~10-12% lower than the powertap.


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## deviousalex

raptor3x said:


> Just to chime in, I just switched from a powertap hub (which I still have) to two separate Stages units for my TT and road bikes. The stages units are consistent with one another, but both are reading ~10-12% lower than the powertap.


That's a lot. Do you know if your power is really one-sided?


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## Srode

I recently broke the rim on my PT wheel and moved the stages from my Synapse disc to the Domane while I sorted out the wheel replacement. While using it found I just about tied (within a few seconds) a PR on a 6 minute climb, but had about 15% less average power output which made me suspicious of the accuracy of the Stages so recalibrated it and it seemed to be still reporting lower than expected. When I got a replacement PT wheel set I left the Stages on and put the bike on a trainer, and road with both reporting to 2 different head sets (500 and 510 Garmins) both picking up 1 second data interval and showing 3 second average power. Both PMs were calibrated at the starte. After a few tests of 100-300 watts hitting the interval buttons on both at the same time I downloaded and compared the data - some had as much as 20% difference between the 2. So I went back and did the same thing with 1 pedal drills (left side only) and the stages reported 2X what the PT reported almost exactly (which it should because it doubles the left assuming the right is the same). Bottom line for my mini experiment, Stages reports very similar data to the PT however I have a significant leg power difference which I am working on. Started by shimming my cleat on the left side (left leg is about 4mm shorter) and also focusing on the left leg pedal stroke regularly while riding. I probably need to do more pedal drills but I'll save that for Winter, I don't want to ruin my good weather riding with drills instead of having fun.


----------



## Blue CheeseHead

Srode said:


> I recently broke the rim on my PT wheel and moved the stages from my Synapse disc to the Domane while I sorted out the wheel replacement. While using it found I just about tied (within a few seconds) a PR on a 6 minute climb, but had about 15% less average power output which made me suspicious of the accuracy of the Stages so recalibrated it and it seemed to be still reporting lower than expected. When I got a replacement PT wheel set I left the Stages on and put the bike on a trainer, and road with both reporting to 2 different head sets (500 and 510 Garmins) both picking up 1 second data interval and showing 3 second average power. Both PMs were calibrated at the starte. After a few tests of 100-300 watts hitting the interval buttons on both at the same time I downloaded and compared the data - some had as much as 20% difference between the 2. So I went back and did the same thing with 1 pedal drills (left side only) and the stages reported 2X what the PT reported almost exactly (which it should because it doubles the left assuming the right is the same). Bottom line for my mini experiment, Stages reports very similar data to the PT however I have a significant leg power difference which I am working on. Started by shimming my cleat on the left side (left leg is about 4mm shorter) and also focusing on the left leg pedal stroke regularly while riding. I probably need to do more pedal drills but I'll save that for Winter, I don't want to ruin my good weather riding with drills instead of having fun.


So the lower power reporting of the Stages did not make you any slower on the climb.  It's all relative. As long as whatever power meter you use reports consistent data, then it is a viable training tool.


----------



## deviousalex

Blue CheeseHead said:


> So the lower power reporting of the Stages did not make you any slower on the climb.  It's all relative. As long as whatever power meter you use reports consistent data, then it is a viable training tool.


Not if you switch between multiple power meters. I have 2 PowerTap G3s for my road bikes (racing and training) and I was thinking about a stages for my CX bike since I switch wheelsets again between clinchers and tubulars but after reading this I'm definitely going to pass. Hopefully the WattBeam double sided reviews are good so I can go that route.


----------



## Fireform

I don't know. I switch among two stages and a powertap and they are all very consistent with each other. I have a history of injuries to my left leg also, but evidently I'm not too unbalanced, at least where leg power is concerned.


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## aclinjury

Since my original post, I've since warrantied one Stages, and had a new battery door on another Stages. And now when compared to my Powertap G3, the 2 Stages report similar power output. So that's good news.


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## rchung

Was there a period of time when one of the Stages had been "fixed" but the other hadn't yet? Did they read differently during that period?


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## raptor3x

deviousalex said:


> That's a lot. Do you know if your power is really one-sided?


It's quite possible that I'm fairly lopsided but I have no idea how to quantify how much. I've done some further testing comparing the Stages to both a Powertap as well as to calculated power values on a nice long steady 7% climb near my house and I'm finding that not only is the Stages significantly different from the Powertap and calculated power (which are both very close), but that the difference seems to be very much dependent on what intensity I climb at. Best case scenario seems to be around a 10% difference but if I do the climb near my limit I'm seeing around a 20% difference. When I thought it was off, but by some constant amount it didn't bother me too much, but this recent finding that the difference seems highly dependent on the intensity has me looking at both the Quarq Elsa RS and Pioneer units as I'm pretty sure I'm going to ditch the Stages.


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## deviousalex

Power2Max drops prices…again. Now $610US. | DC Rainmaker

Seems like this is getting to a good deal. I am guessing stages may drop their prices soon.


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## aclinjury

rchung said:


> Was there a period of time when one of the Stages had been "fixed" but the other hadn't yet? Did they read differently during that period?


hmm sorry for the delayed reply. Honestly since my original post, I've lost tract of events. But I'll try to recall.

First, I warranted one Stages, then got it back. Then I compare it to the other problematic Stages, which has battery door issue. And yes, the average power readings from the newly warranted (fixed) one and the one with the suspected battery door issue are slightly different. However, at this point, the warranted (fixed) Stages read the same as my PT G3. Then Stages sent me a new battery door for the one with the suspected battery door issue, and now all 3 powermeters seem to give similar numbers.

However, I also want note that when I "zero" the two Stages, they give different values (840 vs 880), but their wattage numbers are pretty much the same, which is the same as the G3.

So I'm a happy camper at this point


----------



## raptor3x

Another update, I had to RMA the first Stages as the little tabs that hold on the battery door sheared off. The good news is that the new unit they sent is pretty much dead on with the powertap. There's still some variation if you look at instantaneous data but on average it's quite good. Also, their customer support is pretty fantastic but they really need to rethink the design of the battery doors.


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## aclinjury

raptor3x said:


> Another update, I had to RMA the first Stages as the little tabs that hold on the battery door sheared off. The good news is that the new unit they sent is pretty much dead on with the powertap. There's still some variation if you look at instantaneous data but on average it's quite good. Also, their customer support is pretty fantastic but they really need to rethink the design of the battery doors.


recently I also had to RMA a Stages due to a part of the plastic housing that holds the 3 batterydoor tabs had chipped off. The battery door tabs themselves were all fine though. Sent it back to Stages. They replaced the whole housing unit. The NEW housing unit has been redesigned to be SLIMMER than the original unit, AND the battery door has also been redesigned. 

So yeah, at this point, Stages has their power calibration spot on with the other major powermeters, and now they have also finally redesigned the housing completely (including battery door). I guess that's part of their growing pain eh.


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## Kendogz161

Just to add to this, I have a set of Stages and a Quarq power meters.
On the road these two are with in 5 to maybe 10 watts of each other with ether of the power meters being harder. Now on a trainer or rollers, the stages is always lower by about 30 watts. I don't know why this is.
I have a replacement Stages coming in because of Bluetooth issue. Let's see if there's a difference.


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## spdntrxi

I just had my first issue with battery door.. I have the old one . It went aWol.. Just nowhere to be found after a ride. New one coming. Id love to get the new housing one.. Need to ride my TT bike more .. 6 months left on warranty


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## deviousalex

spdntrxi said:


> I just had my first issue with battery door.. I have the old one . It went aWol.. Just nowhere to be found after a ride. New one coming. Id love to get the new housing one.. Need to ride my TT bike more .. 6 months left on warranty


Seeing how this is such a known problem will they warranty it with the new version?


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## spdntrxi

deviousalex said:


> Seeing how this is such a known problem will they warranty it with the new version?


not unless I have the issues that ACLinjury describes.. they asked me to send a high res picture of the battery compartment so I'm sure they were looking for just that.


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## azdroptop

Installed my stages yesterday and rode the trainer for a hour with it and the G3 wheel on the bike. Two Garmin 500's measuring the values. 5 min and 20 min avg power were identical. Today I rode 34 miles with a few little efforts on flat roads and the Stages showed 52 watts higher on max power and was 6 or 7 watts higher on 5 min, 20 min and total ride avg power. I am pretty sure I am left leg dominate, but I can live with these numbers.


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## rchung

What's important isn't how close they are on average. What's important is knowing when they're not.


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## aclinjury

I'm just checking back to update this thread that I created.

So now, I have 5 Stages in my stable of bikes. All of them have the newer slimmer housing. Stages did update my 2 old housings to the new housings.

So far, the only problem I have had is one of the Stages suddenly started to drain battery overnight. Stages had to replace the entire circuit board to fix this.

Now as for performance update. All my Stages have since track very closely to my Powertap G3 both on the road and on the trainer. Average power, peak power, all track closely to the G3. So, I'm once again a happy camper. At this point, Stages firmware is rock solid. Their battery door and new housing is much better than the old one. This current product should have been the one the release originally. Their original product was really a beta product. Oh well, but at least they have superb customer service. And their customer service was the ONLY reason why I have go back to them and eventually got 5 Stages.


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## aclinjury

rchung said:


> What's important isn't how close they are on average. What's important is knowing when they're not.


yep. When I had my issues, I had to spend some time comparing the power graph of Stages and G3 in golden cheetah, looking for minute anomalies in the graph of the Stages.


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## rchung

aclinjury said:


> yep. When I had my issues, I had to spend some time comparing the power graph of Stages and G3 in golden cheetah, looking for minute anomalies in the graph of the Stages.


If you have Golden Cheetah the easiest way to spot anomalies is to look at their VE profiles.


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## aclinjury

rchung said:


> If you have Golden Cheetah the easiest way to spot anomalies is to look at their VE profiles.


ah thanks for the tips, but what is VE profile?


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## rchung

Aerolab/Chung analysis virtual elevation profile. 

For the Stages and the PT, speed, mass, air density, tires, the road, and aero drag will all be the same between the two power meters. The only thing that's different is the recorded power. So put in the same values for mass, air density, and rolling and aero drag. Any differences in virtual elevation profile will be due to differences in what each recorded for power.


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## aclinjury

rchung said:


> Aerolab/Chung analysis virtual elevation profile.
> 
> For the Stages and the PT, speed, mass, air density, tires, the road, and aero drag will all be the same between the two power meters. The only thing that's different is the recorded power. So put in the same values for mass, air density, and rolling and aero drag. Any differences in virtual elevation profile will be due to differences in what each recorded for power.


Thanks for the explanation! I never new about this until now. Wish I knew about this much sooner in the thread!


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## rchung

People have been comparing averages over rides forever and, like all averages, they obscure exactly where each differed. This way of looking at the data compares the power output second-by-second so you can see exactly where they were different, and what the overall consequence of those differences were. Sometimes one will read lower at one power level and higher at another; sometimes your left leg will report differently when you're climbing hills or sprinting vs. cruising steadily on the flat. By analyzing with Aerolab, you can sprint, you can climb hills, you can coast, you can ride below, above, and right at your FTP and Aerolab will take care of all of the calculation for you.


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## bphipps

aclinjury said:


> I have both the Powertap G3 and Stages. Friend of mine also has a Stages, and before this he also had a Powertap (but he no longer has his Powertap).
> 
> anyway, we both tested our Stages power meters against my Powertap G3, and both Stages meters (his and mine) report about 11% - 13% lower in wattage (normalized power) reading than my Powertap G3. And although he no longer has his old Powertap, he also acknowledged that the reading of the Stages is lower than his old Powertap.
> 
> Even though the numbers between the Powertap and Stages are different, but the Stage is still consistent (precise). Precision of the Stages (as shown by its graphs) mirror the precision of the Powertap. Still, it does bother me that the accuracy between the Stages and Powertap can be at 11% - 13%.
> 
> Does anyone who has a Stage can verify this observation when compared to other power meters I'm most definitely curious.


I've been having this exact issue with my stages DA 9000 Left Crank arm. So much so that my training scores from rides are consistently lower on outdoor rides than indoor training rides. I started noticing it on my Kickr when comparing to the numbers on my head unit connected to the stages. Then when I updated my trainers to a Neo2T the discrepancy between the numbers was even greater. The strangest thing is that it's UNDER reporting the numbers. You would expect the opposite being that power measurements at the crank arm would be higher being closer to the point of force than the hub on your power tap or my trainer.


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## Coolhand

bphipps said:


> I've been having this exact issue with my stages DA 9000 Left Crank arm. So much so that my training scores from rides are consistently lower on outdoor rides than indoor training rides. I started noticing it on my Kickr when comparing to the numbers on my head unit connected to the stages. Then when I updated my trainers to a Neo2T the discrepancy between the numbers was even greater. The strangest thing is that it's UNDER reporting the numbers. You would expect the opposite being that power measurements at the crank arm would be higher being closer to the point of force than the hub on your power tap or my trainer.


Stages tech support is good- it may need to go back to the mothership.


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## bphipps

Yeah I’ve been in touch with Stages and awaiting their reply. They requested I do a 10min pwr test between head unit and stages versus Virtual ride and Neo2T and then send them the fit. files of each


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## aclinjury

bphipps said:


> I've been having this exact issue with my stages DA 9000 Left Crank arm. So much so that my training scores from rides are consistently lower on outdoor rides than indoor training rides. I started noticing it on my Kickr when comparing to the numbers on my head unit connected to the stages. Then when I updated my trainers to a Neo2T the discrepancy between the numbers was even greater. The strangest thing is that it's UNDER reporting the numbers. You would expect the opposite being that power measurements at the crank arm would be higher being closer to the point of force than the hub on your power tap or my trainer.


The Wahoo Kikr is known to over report power by 3%-5%, so comparing to a Kickr (or any trainer) is not the greatest standard. Try to see if could compare it to another power meter (I know many people don't have multiple power meters to play with).

Having said that, I would like to give an update (5 years since my last post). All my Stages power meters (gen 2) are now working as expected.


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## thisisthebeave

aclinjury said:


> I have both the Powertap G3 and Stages. Friend of mine also has a Stages, and before this he also had a Powertap (but he no longer has his Powertap).
> 
> anyway, we both tested our Stages power meters against my Powertap G3, and both Stages meters (his and mine) report about 11% - 13% lower in wattage (normalized power) reading than my Powertap G3. And although he no longer has his old Powertap, he also acknowledged that the reading of the Stages is lower than his old Powertap.
> 
> Even though the numbers between the Powertap and Stages are different, but the Stage is still consistent (precise). Precision of the Stages (as shown by its graphs) mirror the precision of the Powertap. Still, it does bother me that the accuracy between the Stages and Powertap can be at 11% - 13%.
> 
> Does anyone who has a Stage can verify this observation when compared to other power meters I'm most definitely curious.


Yep. I had 2 Stages power meters, one for road and one for CX. I could go out and SMASH myself on my road bike and it would say about the same power level as my CX bike when I was casually cruising. I know that PE is an awful means for estimating power for a number of reasons and I put ego aside and figured my CX was just as likely to be reading high.

However, when I got a Tacx Neo 2T I had a third data point and confirmed my suspicions. I looked at Zwift+Neo data at the same time as Garmin+Stages data and my CX power meter was nearly identical whereas my road power meter read ~20% lower. I sent it to Stages and they replaced the sensor and now all 3 match within 1-2%, which is close enough for me. 20% variance, however, was not.


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