Purely hypothetical. I was a fan of the Metrigear Vector. Metrigear had a cool blog, which inspired me to do some analysis for fun as to how I'd think about extracting power and cadence, and I published those on my blog. But it became less fun when Metrigear was bought out by Garmin and they stopped posting data on-line.


Ah, the good old days!

_________________
http://djconnel.blogspot.com/
Fuji SL/1
Send your data to Weight Weenie listings!

Ah yes, the good old days. Fawning over vaporware is more fun when it is the product of a start-up, which can be forgiven for its youthful, albeit naive, exuberance, than when it is practiced by a big, evil corporation (such as Microsoft, or G*****).

Lots of Stages hating going on here. I think people should give them some time and a chance. This is weight weenies after all, where ever day people make choices that lower performance in the name of weight, but spend more to do it. Here is a product that weights less for what it does and it costs less. I would think it could be a hit on this forum. Whether it works better, the same, or worse is to be determined. Also for all the negativity on here I think people have lost sight of what Stages is trying to do, create a solid power meter, at a much lower price. They clearly state it is not for everyone.

Got an email from them today that the SRAM version our team order shipped today. I have a Shimano one I just installed this week myself, but have not ridden it yet.

For all the negative comments I wonder, do you guys really think your ability to train/race is going to be hampered/lessened if you used this power meter? I have owned 2 power taps, went to a Quarq, and have used an SRM for the last 2 years. I do not personally think the brand of power meter, or it "claimed" accuracy, had that material effect on me. I got better the more I trained, and the better I trained, not because I had an SRM.

Just me 2 cents, flame away.

Yes. The results I've seen indicate that it's not trustworthy for pacing. Might as well just go by PE and HR.

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2013 Wilier Cento1 SR || 2009 Ridley Crossbow || 2011 Yeti AS-R 5 Carbon

OK, I'll flame way! Seriously, almost all of your apologist comments are pretty easily dismissed, but the final one is the real killer. If you train more and better, you'll improve, whether you're using power or not.

If you ARE using a PM to quantify your training, it would help to know that it's accurate and repeatable. There are lots of reasons for this, particularly long-term. Also, it's not "to be determined" if it works the same or better. The drawbacks of measuring power on one side are well-understood, so even if the device itself is 100% accurate and precise, there's still a large potential source of inaccuracy. Bottom line: you'll never know if you're having a good day, or if one of your legs is just having a bad day...

Lastly, I don't get the "much lower price" thing, either? The street price on a powertap isn't actually much higher? You can easily get a used PT or a wired SRM for the same price. Personally, I think there would be some utility if it were much lower in price, or ultimately if it measured power on both sides.

Besides DC blog test what other results are you guys referring to that show the Stages to be inaccurate? I ask that seriously as I have not seen other reviews outside of his that reach negative conclusions.

I have seen the data from two top coaches who rode similar tests with multi PM on the same bike and they each concluded the accuracy was within the 2% claimed. I believe Neal Henderson even posted his data on his twitter feed if you want to look.

This is my main issue with the skeptics on here and in other places. Its definitely OK to be skeptical, in fact its warranted considering the history of PM vaporware, false promises, new product, etc, but I love how people are making claims when they are basing them on one test, one unit, one firmware version, on one guy's blog.

Lets wait to see more data, long term testing, before we:



It could turn out the product is useless. It might turn out to be extremely accurate, or it might turn out be pretty damn accurate and good enough to use as a training tool. Right now people have very little information so its quite comical to see all the "Internet experts" make steadfast claims one way or the other.

No -- it's fundamentally impossible for it to be 2% accurate.

It would be like trying to weigh your tires. So you get a precision scale, weigh the front tire, and multiply by two. You argue the scale is accurate to 0.001%. Doesn't matter. I know tires vary in weight. You can't possibly do any better than your assumption your front and rear weigh the same.

The people who report good results with it aren't doing careful tests. It's really, really hard to verify accuracy or precision with power to anything like 2%. Yet it's important because you're trying to track fitness changes of this magnitude.

_________________
http://djconnel.blogspot.com/
Fuji SL/1
Send your data to Weight Weenie listings!

Bottom line: you'll never know if you're having a good day, or if one of your legs is just having a bad day...



Does this really happen or are we over-thinking things a bit? I doubt the average rider is 60/40 one day then 40/60 the next. I ride the way I ride. If it CONSISTENTLY measures my left leg x 2 then I am ok with that.

My Power2max consistently shows there is no consistency in the way my legs fatigue during my training. When warming up I am biased to my left side and then once I start doing intervals it shifts towards a right bias. As more fatigue settles in my balance might shift more to the right or it might shift back left. I can find little rhyme or reason to the amount of shift or why sometimes it moves back in the opposite direction of where it is trending. The worst split I have seen is ~47% work being done by my left side. I am sure I am not unique and if it were always this way or changed in a consistent manner, then it might not matter. However, this doesn't seem to be the case for me and I am sure I am not some special case.

My understanding is that distribution can and will change with the type of effort, cadence, etc.

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2013 Wilier Cento1 SR || 2009 Ridley Crossbow || 2011 Yeti AS-R 5 Carbon

Umm....I didn't even read the blog post regarding the Stages power meter. I don't need to, because this road has already been traveled. Again, I'm not questioning the accuracy of the device itself, so I don't need to read a review; I'm willing to operate under the assumption that the device is 100% accurate and precise at what it does--measuring power at one leg.

Therein lies the issue. Power is variable between legs. It's variable among different individuals and within individuals. It can be dependent upon power levels, fatigue, cadence, position on the bike (sitting or standing), just to name a few. This isn't news. There's published research on the subject that's over 20 years old:

http://educ.ubc.ca/faculty/sanderson/la ... try%29.pdf

Put into practical terms, you can see how this ends up affecting readings of power meters that measure only one leg:

http://www.saris.com/scienceofpower/200 ... Ergomo.pdf

Before folks start saying "well, that's on an Ergomo", it's worth nothing that the Ergomo has the potential to be highly accurate and precise at what it did (measure power at one leg). The optical torque sensor had some real advantages over a strain gauge sensor, particularly with respect to drift. But at the end of the day, it measured one leg.

I've already seen first-hand the results of measuring power with one leg, looking at the power files of multiple riders who've ridden concurrently with one-leg measuring devices and power taps. Sometimes the numbers agree, and sometimes they vary significantly. The problem is that you don't know when it's accurate and when it's not accurate. In order to do that, or to know if it tends to "work well for you", you'd need a second power meter to provide a reality check, and you'd need to use it under a variety of circumstances. There goes that cost and weight advantage...

So, I'm not jumping to conclusions. I don't need to, because this question was answered long ago: power output between legs is not symmetrical, and is influenced by many factors. A device which measures power at one leg and doubles it is going to be inherently imprecise and inaccurate for certain people under certain conditions, and you'll have zero idea as to whether or not you're meeting these conditions.

Can someone who trains powermeters explain how important ACCURACY vs. REPEATABILITY are?
If you're trying to peg a time trial based on a consistent pace you've hit in training, does it matter if you're 10W lower than what it actually is?
Long-time average power wise it seems to follow pretty reasonably, but in individual sprints, the numbers are way off. I know that software uses various filters over the power data to interpret your workout, but if the STAGES meter incorrectly in the same manner for every workout, what effect does it have on your training decisions? The way I see it, you're still getting a direct measurement of power, so you don't get delayed measurements or transient noise that indirect powermeters (IE: powercal, iBike) provide. But I don't train using a powermeter, so I don't really know what kind of effect this would have.
Obviously if you want to claim you had a 2000W sprint for bragging rights, an inaccurate meter is a nogo.

If your PM is consistent but reads low or high, that's still ok for training purposes. You'll base your FTP, TT power, etc etc off that consistent but biased PM and that will work fine except for e-wang bragging rights. But if you have two PMs, then having a biased one is a problem. They both need to be accurate and consistent.

From DC Rainmaker's review it sounds like the Stages is neither accurate or consistent. And the one leg measurement is going to contribute to both inaccuracy and inconsistency from thr pedaling balance studies I have seen.

But I would like to see Velonew's review before I consign Stages to the land of bad power meters where Ergomo and Ibike live.

Sure. They're both important, but repeatability is much more important. Accuracy is important for a few reasons: quantifying the specific demands of an event (and tailoring your training accordingly), and comparing long-term changes over a period of time (I have almost 15 years of power data, and I've used a lot of different power meters over that time. It's nice to be able to compare the data and establish long-term trends).



No, not really, as long as the difference is constant. And therein lies the problem...




Again, to the bolded part, that's the problem. Pedaling asymmetry isn't going to be the same for every workout, or even WITHIN the workout, so even if the PM works perfectly, it's not going to present the data in a repeatable manner. As far as what effect it'll have on your training decisions, here's a real-world example. I typically do vo2 workouts to failure. If I'm shooting for 350W for 5 min, I'll pull the pin if I can't hit 325 or so. I've seen real-world examples of power files where the agreement between a single-leg measuring device varies by +/- 8%. I don't know about you, but to me there's a big difference between 322W and 378W. As someone who adheres to the philosophy of doing only as much as necessary, I like to know when my power is reduced to a certain level, so I can move on and start resting. That's why I use a PM in the first place. I device with that sort of variance doesn't have enough resolution for me to be of much utility. I'd prefer just to go back to a hill and a stopwatch (seriously).




Well, none of the power meters actually "measure power directly", i.e. they all make *some* assumptions. In my experience though, the assumptions made by the Powertap and SRM are small enough that the data are useful for training and competing. Devices which measure power (indirectly) and then double it put it into the category of "power guesstimator". Power guesstimators are neat devices, and I enjoyed playing around with the Ibike aero, but I certainly wouldn't use the information to make training decisions.

Here's some more reading on pedaling asymmetry, this going back even longer: http://www.ncbi.nlm.nih.gov/pubmed/979569?dopt=Abstract" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

This should answer the question of "how likely is it that I'm just having a 'good left leg day'". Truth is, it's pretty likely.

And again, this is old, well-established research. It's why I didn't even bother reading this dude's review. Frankly, it's not relevant. Even if the device worked perfectly for him, all it would mean is that he happened to have perfect pedaling symmetry during the test conditions. It wouldn't tell me how the device would work for me or others, or even how it would work for him under different circumstances.