I don't want to seem like I have some sorta jihad against Stages or anything. I don't. Really! But the VN review isn't really going to tell you anything useful as it relates to you or others. All it's going to do is test the pedaling symmetry during the test conditions of the guy doing the review. I knew one guy who had a few months of simultaneous PT/Ergomo data, and for him the precision of the devices was consistently +/- around 2%. Compared to all of the other data I've seen, that guy was an outlier, but the Stages will work well for him assuming it's reliable at measuring power on the one side. However, we already know that for most people, power output isn't symmetrical. And of course, unless you're using 2 PM's or a PM which can show pedaling symmetry, you'll have no way of knowing if the device will or won't work for you.

Hmmm. I don't think I was hating on the Stages. I was rooting for the Stages to work well. I want there to be more, cheaper, and better power meters on the market, not fewer. That said, I could only analyze the one they sent. I'm waiting to see if others find the same thing or if by chance we got a bad one. However, the review was fair and Ray posted a link to the data files themselves so anyone can download the exact same files I looked at and examine them themselves if you think I did something wrong. I've recommended that procedure for anyone testing any power meter, not just the Stages: post the data and let others who know what they're doing analyze the data. I haven't seen anyone else post the actual data files like Ray did -- but if you have, please post the link. Some well-known coaches have claimed that the Stages worked for them -- that's good, and encouraging, but they're known for coaching and not for analyzing power meter data or doing rigorous comparisons of the quality of data being produced.



If you do TTs? Yup, absolutely. Two key things with TT'ing are pacing and drag reduction. The unit I examined wouldn't be reliable for either of those two purposes. As for the "consistency and repeatability is more important than accuracy" claim? That's definitely short-sighted and possibly naive. Before I had a power meter I had an basic ergometer that measured power. As it turns out, when I finally got a Power Tap about two years later, I learned that the ergometer was consistent but astoundingly, horrendously, laughably inaccurate. It was consistent and repeatable in the sense that at the same roller speed it gave the same power reading but those power readings were so incommensurate with my (statically-checked) Power Tap that they were unusable. I just tossed out two years of records.

rchung I was in no way talking about you or your guys work. I read what you wrote and I think you guys were very fair and went a long way to explain what you saw and why. It was interesting and a well formed opinion. My comment was more the general tone of a lot of the people on here and people piling on.

Personally like you said I route for the small guy, I want them to succeed and see them work. I think what these guys are doing is really interesting and if you compare them to what Meti Gear said they were going to do, Stages deserves credit. They have a workable product and only a few months after launch they are shipping it. I look forward to taking my SRM off and giving it a try.

Thanks.

One more thing: Stages sent out a firmware update a week after Ray's review and said that it addressed something in our analysis. I don't know what it was and I don't know if it fixed everything we saw but I'm happy that they acknowledged that there was some validity to our work, and whatever the fix was you'll be getting an improved product because of what we found. That's a win for everyone.

I agree. Compare that to some other brands, e.g. Garmin, that have been working on their products for ages and still have no idea when they could ship the finalized product. Also, the price of Stages product is much closer to what a PM should cost. Although Garmin was originally talking about bringing the PM training to the masses, their (possible) product seems ridiculously overpriced as is the case with other brands also.

Unfortunately Stages is so far of no use for me, as it is not compatible with Campagnolo cranks.

@RChung when you were using the inaccurate ergometer were you doing interval workouts with it? And if so are you faster or somehow better now that you are using a more precise meter.

I ask because most people use a PM for training and I haven't seen anything that suggests a whole lot of accuracy is needed. Its certainly nice to have but I'm not at all certain that it results in a fitter faster athlete.

Styrell,

Are you sure you are not confusing accuracy with precision?

ANY tool - no matter what it is, be it a powermeter or a drill or simple ruler - must have some accuracy in order to be useful. It does not necessarily have to be extremely precise, but some precision is necessary.

Easiest two examples: a ruler and a hammer.

A ruler is a measuring tool, correct? It tells you the dimensions of an object. You rely upon it's accuracy (ie, the lines on the ruler don't move), even if it doesn't have precision (the ruler you may have only goes to cm, not mm, or the lines on the ruler themselves have thickness, however the thickness is constant) If you had an inaccurate ruler, one where the lines don't remain at fixed locations on the ruler or if the lines are not placed at reliable, consistent intervals along the length of the ruler, would you still use that ruler?

A hammer. A hammer is a really simply tool - it is a weighted object with a blunt surface that enables object to be driven by transfer of force into or through a surface. You rely heavily upon its accuracy, not its precision, but you take the accuracy for granted. What would an inaccurate hammer look like? The head of the hammer would not have a level or hardened surface. Even a ball-pean hammer wouldn't have a ball end with any consistency of shape. The weighted end of the hammer might fluctuate throughout the swing of the hammer, meaning you may not necessarily have the force you intended to be placed at the end of the hammer's swing, but it may randomly end up closer to your hand. That is an inaccurate hammer. Would you use it?

A scale. We use scales a lot here at WW. We love them. We rely upon their accuracy, and if we have a nice scale it would have high precision as well. Let's see what an inaccurate scale would look like:
-You weigh yourself on a scale, say it comes out to 150lbs.
-Tomorrow you weigh yourself on the same scale, it comes out to 120lbs.
-Two days later you weight yourself on the same scale, it comes out to 140lbs.
That is an wildly inaccurate scale - there is no way, unless you lost a limb and grew part of it back like a lizard, that you would lose that much weight in 24hrs and gain half of it back in the next 24hrs.

However let's say you have a mildly inaccurate scale, one within a few percentage of reality. That scale tells you you are 151lbs the first day, 150lbs the second, and 151.5 the third. Is it in accurate? A little bit, but it is within an acceptable range of inaccuracy.

The issue being claimed against the Stages powermeter is too much inaccuracy. Can some inaccuracy be acceptable to use for training purposes? Yes. If it is too inaccurate however, to the point of being unreliable, then it is not good.

What came through from Rainmaker's test was that he compared Stages powermeter readings to other powermeters. Sort of like putting rulers next to each other. They may not each read "224 watts" - one might say "224" another might read "220" and another might read "225" but they are within an acceptable range of accuracy. Stages comes along and says "220" initially... "GREAT!" you think... but 5 minutes later, the other powermeters are reading 250, 252, 251 respectively, and Stages reads "140" That points to Stages having too much inaccuracy.

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Thanks for the lesson, but you could have saved some electrons, Yes I meant accuracy.

2nd your description of therelative acuracy of stages vs the other two PMs in the test is fictional. The other two PMs didn't always match to a few watts, far from it they were frequently over 20 watts apart from each other and occasional the higher one became the lower one.

3rd, and what was really my point, How much accuracy is needed for a typical cyclist training using a typical training plan? If its plus or minus 2 watts, none of the PMs tested is worthwhile. If its worse than that how much worse is acceptable? Someone reading a lot of these posts would get the idea that the more accurate a PM you have the faster you will be, all else being equal, I don't think thats at all true

"the faster you will be"

What does that even mean? What are you talking about?

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The inaccurate ergometer was absolutely, horrendously, infuriatingly, laughably a problem. In ergometer mode, the Tacx was supposed to adjust the load so that whatever speed you rode, the power would remain constant. So I did some initial tests in order to estimate my (then) FTP then would set the ergometer at 250 watts and do intervals. Back then I figured, hey, maybe the ergometer was off so 250 watts was really 240, or 260, but as long as it was consistent then everything would be okay. So I'd get on the ergometer, set it at target wattage, and ride. Simple.

Here's the problem. The ergometer was consistent in the sense that every day it would read the same thing. And it was consistent in that it adjusted the load the same way every day. However, it adjusted the load inaccurately. Now fast-forward to when I checked the Tacx against a known-good Power Tap. Here's a plot:



There are three groups of dots of different colors here but you can just focus on the black dots marked "scale = 100." In an ideal world, if the load generator had been working well and accurately, each group of dots would be horizontal, and the percent error (that's the y-axis) would be constant. Then you could just adjust for the constant error upward or downward to get the true power. (And, yes, for those black dots there really were times when the Tacx was reading 40% high).

But what you see is that the dots aren't at all horizontal. They're seriously, horrendously, dependent on speed. So I had been setting the ergo wattage at a particular level but the load, unbeknownst to me, varied with speed. Once again, look at the black dots. If I set the ergo wattage at 250 watts and pedaled at an indicated speed of around 24 km/h, the Tacx would have actually been accurately producing 250 watts of load. However, if I set the ergo wattage at 250 watts and pedaled at an indicated speed of 35 km/h, the Tacx was in error by close to 40%, so the actual load was only about 150 watts. So naturally I had gotten into the habit of pedaling at high cadence with big gears because that "felt best." It felt best not because my body somehow liked high cadence but because the ergometer was inaccurately adjusting the load.

So when I got the Power Tap (which I checked with known weights) I stopped using the Tacx. It had set me back by more than a year.

And, as for your continuing claim that the Quarq and PT were also off by a lot, I've already explained that to you over in that Slowtwitch thread: it's not that the Quarq and PT were off it's that when they were off we know what that was. We had agreed ahead of time when we were setting up the test protocol that he would manually re-zero at certain points in the tests. One of the times in the first outdoor test he improperly re-zeroed either the Quarq or the PT and then the two were offset by a fixed amount. When he finished that segment of the test, he re-zeroed again as we had always planned, and the Quarq and PT synched up again. The Stages didn't track nearly as well during that ride and continued to drift. As for the 2nd outdoor ride, Ray had to stop to take photos right after bringing the bike outside, then forgot (against the protocol) to re-zero before starting off. Since the first couple of miles from his apartment out to the test site included stop lights and traffic, he coasted a couple of times, during which the PT appears to have automatically zeroed. Part way along the ride he thought, "oh crap, I forgot to zero" and backpedaled on the Quarq. However, before he started the test loops at the target site, he stopped and did a manual re-zero on all three, per the protocol. Here's an important part that you don't appear to get: we didn't edit out or manipulate the data to mask out those sections: we knew we were going to post the entire data files (which, once again, no one else has done) and instead added explanatory notes in the accompanying text file about the re-zeroings. We plotted the entire data, warts and all, and relied on people to read the notes -- and then to understand what they meant. So, honestly, tell me the truth: wouldn't you have squealed just as loud if we'd snipped off the beginning of the 2nd ride and the middle of the 1st ride? I still think it was better that we post the entirety of the data files and include explanatory notes but you're starting to make me think maybe not.

Most people that buy PMs do so for training. The idea being that training with PM is better than training using perceived exertion or a HR moniter. If someone told me they have a device that allows "better training" my thought is it will allow me to get faster.

@RChung. I think I still have one of the Tacx units in my basement, yeah that thing sucked . I always had the idea that what ever was adjusting the load couldn't react quick enough or just didn't have the power to keep a decent load steady.

Robert, most of the explanation on ST was that "we know DCRM did the test wrong", but no where did I read as much detail as you just posted. He did do a number of rides and posted lots of data. I would like to see a section of an outdoor ride, of reasonable length, say 20 minutes, where a PT and Quarq were compared by the differences.

Aside from that, if I were to buy another PM I wouldn't be happy with the current issues with Stages, nor would I be happy with the current issues with a Quarq. Too many posts about drift and too much need to re calibrate. Its fine for the testing DCRM did, but I'm just not ging to do that every ride.

There's about a 20 minute section in the middle of the 2nd outdoor ride where Ray was doing laps on a closed course. Ray zeroed all three just before and just after that section. If you examine that section you'll see that the PT and Quarq tracked each other but that the Stages drifted downward. What we don't (can't) know is whether that was because of change in the Stages or a change in Ray's L/R balance. However, if he had been trying to do a workout at a set power we know that the workout would have been different if he'd been going by the PT or Quarq than if he'd been going by the Stages.

Interestingly, (and I think Connelly knows this) when I first saw these data files I presumed that Ray was right leg dominant because the Stages was reading lower than the PT and Quarq. However, when Ray tested a set of Polar/Look Keo Power Pedals which, if you recall, measure the right and left legs separately, that came up with him being left leg dominant.

Thanks, if its the section I think the Quarq and PT varied from each other by 4-14 watts, not bad but not great.

But before and after that section their was much greater variation and all three segments were shifted in relation to each other. Like I've said I would want something more robust than having to re zero every 20 minutes, and my guess is that almost anyone who read exactly what DCRM did during the test isn't thinking that he should have had to re zero more than he did.

Hopefully the adjustment Stages did will help, but I think they are either going to have to improve how the accelerometer measures cadence or ditch it and go with a reed switch.magnet set up.

Excellent...

If I were to take 21 thousand cyclists and divide them in groups. One group of 1000 gets a perfect power meter. Another gets power meters 1% precise. Another 2% precise.... finally I get cyclists with a power meter 20% precise. They all do equivalent training plans for 12 weeks. If power is good for training, then those with the perfect meters should be faster at the end of the 12 weeks than those with 20% precise meters (the latter no better than perceived exertion and a stop watch). In between there will be a smooth curve of some sort. I should be able to model how much faster an extra 1% of precision makes me.


If not, then power meters don't help with training.

Stages has a separate issue, though, which is those with L-leg power versus those with 2-leg power at the end of the 12 weeks may have trained themselves to ride imbalanced to the left side, since the body tends to find the lazyist way to accomplish a goal, and if my goal is to see a certain number on my power meter, right-leg power isn't doing much to help me reach that number. Why waste effort?

So I'd rather have an unbiased imprecise power meter like iBike than a biased imprecise meter like Stages (iBike has other biases, but ignore that for now).

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