Stages Power Meter crank and Powertap PRO+ wheel fitted to same road bike on the same ride.
Video is of the recorded telemetry overlaid on the GOPRO video of the ride.
Also some stats at the start of the video showing, in general, how close they tracked each other etc.
In a nutshell there was 3 watts difference over an hours ride, although there was greater variability within certain recorded strava segments.
I have had issues with both power meters and have no vested interest in either - just though it would be interesting to do the comparison, I’m certainly no scientist though.
For some 3 watts is earth shattering and the could result is a fracture in the fabric of the universe.
What’s really needed, and that’s of greatest importance for those using a PM for training and pacing, not aero testing, is how repeatable it is day to day, week to week and month to month. So comparison data over a period of several weeks over a range of workouts is needed.
I actually had someone contact me asking about my Stages wondering that same question. I don’t have hard data, but my gut at least tells me that it’s repeatable between similar efforts and types of riding… and especially with temperature variations. My gut also tells me that my Timex Cycle Trainer is a PITA as it only displays 1s power values which is magnified with 1 sided power measurement making it very hard to use for pacing. I’ve begged Timex for a software update… but apparently it would involve a MAJOR product revision… and that’s not happening anytime soon. DCRainmaker did warn of that issue in his review. A Garmin 500 is arriving today to replace it.
I wonder if Stages is possibly doing this with some of their sponsored athletes and teams?
For some 3 watts is earth shattering and the could result is a fracture in the fabric of the universe
No, it isn’t, but while the average power for a 3 hour ride may come up relatively close, most days, sections within that 3 hour ride can be very different. That is something that the MMP chart can sometimes reveal quite quickly.
As you say, it is important for training and pacing, if there are intervals or hard sections in there where data is very different, that may be bad. This can also effect NP quite a bit more than AP, which can affect people who use TSS to track training load. The extent to which this is a problem will vary from person to person, and day to day, and how they use their power meter.
But yes, repeat-ability is important, and that is the biggest flaw with the stages, you can’t count on your l/r split being repeatable. Nobody really has a problem with its ability to measure left leg power consistently, it seems to do that well, even accurate too (which is important no matter how many people in their first year of power meter use think differently)
Normally my powerbalance has consistently been 51/49 R/L on my rides, like for the past 6 months or so. This weekend I had two good rides that saw an improvement in my numbers, but my balance on both of the rides were 53/47. These rides saw a big improvement in my best 1 hour power and also much higher average power for ~3 hour rides on the same route as a few weeks ago. If I was using a stages, the average power that I would have seen would have been maybe 3 watts higher instead 12 watt average I measured. So with a stages I could have gotten the impression that all of my hard training did not result in that big of an improvement, which is bad for motiviation and possibly worse I could change my training (training that was clearly working, but stages could give the impression that it was not working well).
In other words, a single ride , especially just looking at averages, is not a very good test. Seriosly, my balance was pretty consistent over months, but then changed. On a stages how would I know that?
I will quote a certain forum member here (cough)Chung(cough)Chung and just mention that the most important thing is to look at where the powers differ, rather than where they are the same.
Normally my powerbalance has consistently been 51/49 R/L on my rides, like for the past 6 months or so. This weekend I had two good rides that saw an improvement in my numbers, but my balance on both of the rides were 53/47. These rides saw a big improvement in my best 1 hour power and also much higher average power for ~3 hour rides on the same route as a few weeks ago. If I was using a stages, the average power that I would have seen would have been maybe 3 watts higher instead 12 watt average I measured. So with a stages I could have gotten the impression that all of my hard training did not result in that big of an improvement, which is bad for motiviation and possibly worse I could change my training (training that was clearly working, but stages could give the impression that it was not working well).
In other words, a single ride , especially just looking at averages, is not a very good test. Seriously, my balance was pretty consistent over months, but then changed. On a stages how would I know that?
Very true. That’s a legitimate risk. Ignorance is bliss on a Stages. However, there’s also greater potential for calibration errors and temperature variation error on other power meters I believe. So you can’t say with certainty that it was in fact a 12 watt improvement either. I’ve zeroed mine 4 or 5 times since installing it and have yet to see a significant change in the calibration value… and it of course auto compensates for temperature. Though I’m not sure how much that influences power if the outdoor temp goes up lets say 15F during a ride.
Please do not turn this into a left right leg debate. Done to death already.
I would be really interested to see the file if Jackmott gets the data to produce it.
Always remember - even if the file shows great differences in places, there is nothing to say the powertap is right and the stages is wrong. Might be the other way around.
Please do not turn this into a left right leg debate. Done to death already.
You personally may not want these details – which is ok. But asking to understand the conditions under which they differ is hardly a left-right leg debate. Standing climb, sitting climb, low cadence, high cadence… it’s really good to know when things differ.
I would be really interested to see the file if Jackmott gets the data to produce it.
Of course! That’s not at odds with what I’m saying, though.
Always remember - even if the file shows great differences in places, there is nothing to say the powertap is right and the stages is wrong. Might be the other way around.
Who would forget this fact, though? I would like to see where they differ, that’s all.
Always remember - even if the file shows great differences in places, there is nothing to say the powertap is right and the stages is wrong. Might be the other way around.
Normally my powerbalance has consistently been 51/49 R/L on my rides, like for the past 6 months or so. This weekend I had two good rides that saw an improvement in my numbers, but my balance on both of the rides were 53/47. These rides saw a big improvement in my best 1 hour power and also much higher average power for ~3 hour rides on the same route as a few weeks ago. If I was using a stages, the average power that I would have seen would have been maybe 3 watts higher instead 12 watt average I measured. So with a stages I could have gotten the impression that all of my hard training did not result in that big of an improvement, which is bad for motiviation and possibly worse I could change my training (training that was clearly working, but stages could give the impression that it was not working well).
In other words, a single ride , especially just looking at averages, is not a very good test. Seriously, my balance was pretty consistent over months, but then changed. On a stages how would I know that?
Very true. That’s a legitimate risk. Ignorance is bliss on a Stages. However, there’s also greater potential for calibration errors and temperature variation error on other power meters I believe. So you can’t say with certainty that it was in fact a 12 watt improvement either. I’ve zeroed mine 4 or 5 times since installing it and have yet to see a significant change in the calibration value… and it of course auto compensates for temperature. Though I’m not sure how much that influences power if the outdoor temp goes up lets say 15F during a ride.
The quarq for both of those rides is very stable. The manual zero value before one of the rides was 40 and at the end of the ride was 39 (This was a bike going from inside at ~68 degrees to outside at something in the 50s, so temperature does not affect things much). I also auto zeroed about 15 minutes into the ride and maybe one other time. So yes there is uncertainty on the 12 watt value, but even for that, I do not see how a drift would affect the balance value.
Stages does appear to measure the left side power accurately, compensates temperature very well, and is very immune to installation errors. I just think that measuring only the left side is a huge drawback. If they could also instrument the right crank arm, they would have a great product.
Why have you only zeroed 4 or 5 times since you have installed your stages?
Seen that. It makes no odds to the data you will hopefully receive. Had the argument with a track guy here in the UK comparing a stages to a powertap. I only wanted him to show me the powertap had been compared to something else so he could show me it was working properly - he could not. The stages firmware has undergone many updates since the Rainmaker review - just really interested to see the data to be honest!
I only wanted him to show me the powertap had been compared to something else so he could show me it was working properly - he could not.
I’ve always wondered what the “gold standard” power meter is for developing a power meter. The static force calibration is one thing, but that just tells you static force.
Maybe SRM has some bias, and all the other manufacturers copied the bias so they could match SRM!
For some 3 watts is earth shattering and the could result is a fracture in the fabric of the universe.
Average power over an entire ride is really THE lowest bar to cross in evaluating the output of a power meter in comparison to another…especially if the ride includes any coasting, since most PMs report zero power fairly accurately and precisely :-/
For those questioning the comparisons to a PT…they have been shown to be VERY accurate and repeatable through countless tests over the years. My experience with various PT wheels is that they are either dead on, or they don’t work at all (very rarely). The coasting auto-zero is a BIG part of that IMHO.
In any case, the fact that they have been shown to be accurate and precise despite not being able to modify the torque slope by the user says a LOT in my book…
