This is false. In one of our threads several months ago, multiple people, including me, showed hard data that demonstrated single-sided PM readouts inaccurate relative to dual-sided data.

A properly functioning Favero is probably one of the most precise & true PMs on the market when it is measuring total power. When single-sided, precision and trueness are unknown.

In the OP's case, there is a reasonable possibility that the Favero is not functioning properly, in addition to its single-sided limitations. It could be miscalibrated or it could be producing bad readings if the bearings are worn.

Was this with a Favero? I'd like to see that thread!

There's always a small possibility the Favero isn't working, but given that OP is not reporting any weird precision fluctuation errors and its proximity to the Flux readings, I'll bet 95%+ that it's working fine. Faveros are really solid.

Utter and complete nonsense. There are numerous demonstrated examples of single sided power meters providing very poor data as a result of L/R variance and it's not that uncommon. My wife and I both get very inaccurate readings from single sided power. In my case, average power was 10% too high as I am left leg dominant. But it's not just a matter of applying a scaling number to my power numbers, in my case my leg discrepancy is pronounced at low power and gradually becomes more even at high power. As far as I'm concerned, 10% error is enough to make the numbers total junk. If I had all my history from a single sided power meter and switched to a double sided power meter, my entire power history would be totally useless and I'd be starting from scratch.

You missed the part in my post about " and has the necessary knowledge to understand if their devices are actually accurate".

In the case of our household, I've actually performed the test Tom A. mentions against one of the Quarqs. We have FIVE devices including that one that agree almost exactly. And we have two devices that disagree by wildly varying amounts. You really think I can't trust the five and discount the two outliers?

It's not as hard as you make it out to be to understand if a device is accurate, but it does take some knowledge and ideally multiple sources of power.

If you intend to train with power and don't expect to use the same device for the rest of your training career, accuracy is just as important as consistency. And as I mention in the post above, single sided power can be both inaccurate and inconsistent, as leg discrepancy can vary depending on power output, level of fatigue, injury, etc.

You seem to have an expectation or confirmation bias that prevents you from understanding the trueness and precision issues with a single-sided PM. You are arguing "You will NEVER convince me that your training and performance is compromised by using a Favero Uno vs a Duo." This may true for some. But it is a different argument. Others are arguing here and elsewhere that a single-sided PM lacks accuracy relative to dual or total power PM, and the loss of accuracy is unknown for every individual user. It is possible that both arguments or true. Or not. One thing is certain though; the second argument is true.

I am in violent agreement with you that the Favero sensor is one of the best in the market. Yet, even in all of its greatness, if the user does not have a perfect 50-50 power balance all of the time, the collective trueness and precision of a best-in-class Favero sensor in a single-sided environment is a complete unknown.

Here is one of several specific examples of others have posted that show single-sided PM inacuracy. https://forum.slowtwitch.com/...ost=7100178#p7100178

I guess I am being pendantic, what you have is agreement, no one knows if any of the devices are accurate. So what you are conflating is accuracy which is a well defined term vs agreement. We agree that having a reading that is transferable is useful but there is no way that I am aware of to determine the accuracy of a bicycle power meter, and to date no one has educated me otherwise. This discussion has happened here before, to the same end. In general I think we agree, I am just a stickler for using the term accuracy when there is no internationally accepted standard to which a bicycle power meter can be calibrated against to certify it is "accurate". Just because 5 meters agree means they are consistent and agree in their output that is all, they all may be equally inaccurate.

Hah that thread sucked!

Including the 100 percent bogus scenario that user thampton presented which I questioned the reality of and which has no response as expected. Seriously his scenario had someone gain watts to ftp while LOSING 8 watts in one leg and gaining like 16 watts in another leg. Yeah that’s realistic.

Look I’m not going to deny that dual sided is very slightly more accurate but all this commentary on how one sided is inaccurate , not precise, not unfold enough for training is 100 percent bogus when talking about favero unos. It’s almost certain that if you think the dual to single version is costing you training quality and thus improvements, I’m not buying it.

https://www.mcmaster.com/1788T74/

I know people who have bought these for use with calibrating power meters for accuracy (NIST certified). So, now you can't say you haven't been "educated otherwise" ;-)

That said, one can also get good results using weights that have been weighed on a calibrated scale.

You're welcome.

Oh yeah...and I'm one of those who see fairly large L/R discrepancies, depending on power output. MANY years ago I described here on ST how my L/R balance varies from as large 56/44 when at below threshold power, to basically 50/50 at threshold and above. Any effort below 40K TT power is going to show up to an 8% error due to that. Trying to evaluate an Ergomo power meter at the time for a ST review was an exercise in frustration (with the L only power measurement a big part of that).

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http://bikeblather.blogspot.com/

Tom, TOm TOM, as an engineer you know better than that..... a calibrated weight is not a means of certifying a power device, power is the rate of doing work, tell me how a weight will give you that calibration, it will tell you that maybe under a certain load the strain gauge reads x strain that is proportional to the mass but it is still a matter of more than that to get from the load cell to a power reading.. sorry I remain unconvinced. Your might also be able to extrapolate to toque? What if your cadence sensor is slightly off how could that effect your power reading.... how does the calibrated weigh take that into account? Though I enjoyed your try... I calibrate analytical balances daily to NIST calibrated masses. The calibrated masses will not tell me the power output reading on my power meter is correct against something reading in the same units ie watts.

Consider me still unconvinced but I am open to hearing a more convincing argument.

No one said "... for training." That is purely you inserting that subjective conditional acceptance of the Uno inaccuracy.

Multiple people in that thread and other threads demonstrated data-based examples of single-sided inaccuracy (both lack of precision and lack of trueness). That is hard reality, and 100% true.

Whether anyone wants to accept single-sided inaccuracy is a personal value decision. But, it is absolutely real that single-sided PMs inject <5% error for many people. For me, a single-sided PM would read 4% to 10% high (depending on intensity, cadence, position, and fatigue) and average around 6% high overall. That is unacceptable to me. Based on the feedback in multiple threads, many people share similar feelings and are grateful to understand the limitations of single-sided PMs.

Obviously the one that reads higher!

You forget that power is merely multiplying the torque value by the rotational velocity.

As I said earlier, measuring rotational velocity accurately is fairly trivial (it's basically just counting), and a standard error analysis will show that the largest contributor to the power value error is going to be in the torque/force accuracy.

BTW, did you know you can do a static force check even on your Faveros? https://www.dcrainmaker.com/...atic-Weight-Test.pdf

At a minimum you'll know it's accurately measuring one leg then, at least :-)

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http://bikeblather.blogspot.com/

Is it possible to do a static force check on Powertap P2 /Quarq Pedals?
One of my pedals is reading way far from accurate.

According to Ray's chart at the end of this review, that answer is "no": https://www.dcrainmaker.com/...p-pedals-review.html

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http://bikeblather.blogspot.com/

Thanks all for your replies. You've provided a lot of food for thought. I'm fairly new to stuff like smart trainers and powermeters. There's much for me to figure out and see how these things can benefit me.

Thanks and stay safe on the roads and everywhere else as well.

Nope I did not forget that power is merely multiplying the torque value by the rotational velocity., what you forgot is that you have a device to measure rotations called a cadence sensor that may be off, you also forgot there is a temperature sensor in the meter to deal with temperature effects on the strain gauge, both of which you did not verify nor calibrate. So though you did get a calculation for the strain and assuming that strain gauge is in fact linear, you only verified one point then no you did not come up with a calibration to a known standard. Still waiting for a convincing argument to the contrary. To many sources of uncalibrated error in your assumptions.


The closest I have seen to a convincing argument for determining the correctness (still not calibrated or compared to a known standard) is the first principles calculation that a prof did using a treadmill on an incline and then using the first principles calculation for motion since aerodynamic forces are zero. It said in that case the power meter was reading a reasonable value based upon the calculations. So it suggested that the readout was within a reasonable measure of what it should have been.



But enough accuracy, if the machine is reading reproducible (ie precise) and it compares favorably with others in the field that is good enough for me. I can train with it and get meaningful feedback from it but I would never waste my time comparing one meter to another.

You are entitled to your opinion. And to share that view, that's the world of the internet forum.

However, I disagree with your stance. Running some tests could show if one of the feeds is dropping out data, or providing highly illogical / non linear responses which could indicate a fault / which source to trust. May not, but could do and costs nothing aside from an hour of time.

OK, I'll give you that a simple and quick comparison of the files in something like Golden Cheetah, WKO, or the DCR tool may show that sort of gross technical fault, although you don't even need to compare them to determine if there are significant dropouts. But even if one of the devices shows such a problem it still won't tell you if the other one is actually accurate. Neither device can be considered fully reliable, the Uno because it's single sided, the Flux because according to DCR some of those trainers have had accuracy issues in the past. So of limited value. There are ways to verify if the devices are accurate but simply comparing the files won't tell you that. If he upgrades to Duos and installs and calibrated them properly, their reputation would give one a reasonable probable accuracy.

That's what Maier et al. did for their study on power meters. Here's Figure 3 from their paper.




In addition, I've done CdA and Crr tests on roads where I included coasting (and thus, where the power was zero) and then ramped up the power up to as high as I could go while still maintaining my position -- then back down to zero and coasting, then lather, rinse, repeat. If the power meter is off, then the CdA and Crr estimated from the zero power coasting bits won't agree with the powered bits.

People used to send me power meter data files to help them figure out their CdA and Crr. I learned pretty quickly that if they had a single-sided power meter, the data were too noisy to use so I used that as my first question to cut down on wasted time. That isn't to say that a dual-sided or total power meter was right and accurate -- just that if they had a single-sided PM, it almost never was accurate or precise enough to use for this particular purpose.

Simple answer is... Use the numbers of the power meter you will race with.

Do however check your setup and calibration process and look for issues of power drops/spikes that could be a sign of the power meter failing.

Power2Max is generally considered one of the more reputable manufacturers of power meters. When you purchase their NG Eco PM, you can opt to spend an extra $100 to get claimed 1% accuracy instead of 2% accuracy. There is zero hardware differences between the two versions; the only difference is that the 1% accurate PMs are tested dynamically. The 2% meters are tested with, guess what? A static calibration rig with a known weight, the same procedure Tom A. is describing.

Sure, dynamic calibration is preferable, but static calibration is a very reasonable way to test PMs for the end user. I don't think any of us would argue that the difference between 1% and 2% is going to cause a meaningful difference for using a power meter for the purposes of assessing the effectiveness of one's training, unlike, say, the 10% error I saw with a single-sided PM.

If this is the case, any idea why P2M does not support static calibration ?

I'm late to the party but if borrowing equipment to "stink test" isn't an option for folks, find a really steep little section of road in town. Even if very short. Just long enough for maybe 30sec of power data.

Weigh yourself with bike and all kit. Then climb it trying to hold some constant speed or power. Preferably when not windy and slow enough that it's more CRR/climb than aero drag. Then plug into the aeroweenie calculator. Grab the CRR from bicyclerollingresistance.com.

It's not a 100% thing but it can probably sniff out a 20w or so problem.

My left only stages is pretty much just a kilojoules tracker for outdoor riding. If I "care" about a ride due to doing intervals in upper zones, I will toss the file through the fit file fixer and boost the power by like 3% or so knowing the left stages is so far off my other meters and trainer I trust more. Otherwise, kilojoule/calorie counter.

You can do this more or less by just looking at your Strava segments that you use repeatedly - there should be tons to choose from. Just by looking at the ones you do frequently, especially for z3 efforts which are sustained harder efforts for a fixed duration, you should be able to see if the power is fluctating by 20 watts pretty easily.

Honestly, it seems like everyone bemoaning SS is using Stages or older-gen PMs.

I've posted earlier about this, but I've been using 2 separate Favero SS for 2 years now, and there is not a single segment on Strava ,be it a 30 second sprint, or a 45 minute climb/TT segment, that makes me question the power - every single segment I've done across 2 PMs are so accurate that you can gauge my fitness down to what seems like the watt on each workout in the leadups to my race. On bad days, the wattage is down, and on strong efforts its up - in pretty much every case, I the power is so reliable that it differs by less than 5 watts from what I expect, at in worst case scenario, less than 7-8. Literally never 10 or more, and I'd say 95% only 5 watts. Heck, I did 3 Oly races in a 3 month period on flat, hilly, and mixed courses, and I rode to RPE without targeting any specific wattage, and my Faveros pegged my overall race power at 250, 250, 251. I wasn't surprised at all - that's the typical kind of watt output consistency I see with my SS Faveros.

I think with the modern tech today, we should limit the SS vs DS argument to Faveros or similar-gen SS PMs. The stages singles are old, out of date, and have been almost always the single offender for those claiming 20 watt type error. 20 watts is so far out of the universe of error in my Faveros it's absolutely ludicrous.

I was late to the party as well.

No secret I use my PMs for aero testing. I have a P2Max, 2 PTs, a set of Faveros and a single side stage. I also have a Computrainer and a Kickr. My P2Max, PT G3 and Faveros are the ones I trusted. My CT as well.

I have gone back and forth and what I should use as my reference PM for aero testing. I have decided it will be the Faveros after a disappointing email exchange with P2Max on why I didn't need to static torque test. This led me to this thread.

The Faveros seem to be the only ones that aren't doing Voodoo magic calibration on the fly and that I can do a static torque test whenever I want to double check them.

I'll post a little more late in the aero sensor thread but I was analyzing an aero test from a ST member and he seems to have voodoo calibration variation during his session, which of course throws off relative (A vs B vs A vs B) aero testing