Hi,

I will try and answer this. You have some differences inherent to where power is measured. Generally speaking, the closer to you (read the crank) the closer the power measurements are to your 'real' power. You have to also keep in mind that a left side power meter takes your the measurement from you left leg and doubles it. Most people have an imbalance (my right leg is much stronger than my left) so a left side power meter would mean that I would lose 25% in power measurements (yes the imbalance is that big and I am working on correcting it). If you do single leg squats, for example and see a significant difference you may find that partially explains the imbalance. You could look into making sure that your power meters are calibrated and have temperature compensation which can also create some differences. In the end, you should only compare apples to apples (left side power meter to another left side power meter and tax with a Kickr for example) with what I mentioned in mind. I have a Kickr Core and a 4iiii left side only (which I will upgrade soon to dual) and I am sure that if I paid attention to the numbers they would be quite different but I don't. Most of the reputable power meters are usually accurate to +/- 2% and what you really want in a power meter is consistency/reliability. When riding indoors I suggest only using the trainer for power and when riding outdoors use the left side only, keeping in mind you might see 10-15% difference and just ignore it as long as the wattage is consistent for the left side (you can compare on your most common routes over time).

I hope this helps and stay safe.

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"see the world as it is not as you want it to be"

I use Rotor INspider.

Ok, firstly the max power is where it's really expected to be fair differences, and so actually those are really close. It's the average that's the one which is unusual.

But really to understand you need to record a ride or two using two head units (use an old device, borrow one from a mate). And then get the *.fit files and upload into DCRainmaker Analyzer to compare.

At low powers then depending on the gearing you use then I've found the tacx trainers (neos) pretty meh in terms of power. It's near their floor. Equally one legged powermeters when just pootling could also be at their least accurate depending on your pedallign style/skill.

You cannot expect any degree of precision with a single sided PM

Within a single ride, my R/L balance can swing from 45/55 to 55/45

I’d use single side as a directional estimate and the flux as your source of truth

My first reaction is 143W vs. 115W is a massive difference. Something must be wrong.

I lean toward the Flux S as the one OK, since a 115W workout is barely touching the pedals. So, look in your Garmin for signs that the Assioma was dropping out or irregular. Maybe it will be obvious there. Then look for the same in your Tacx file. The nut is, do the charts appear to generally represent what you did, or do they have any spots where they jump around. But, other than that, there is no sure way to know which one is misbehaving.

But...As long as it's consistent it's OK!

In no particular order

- Double check you have the crank length properly set or the pedals will be off.
- Double check that you have properly put the washer on the Assioma pedals when needed. If the black "cylinder" is touching the crank arm your numbers will be off
- Try doing intervals at 150, 200, 250, 300.....and compare the intervals. You may gain insight
- The L/R imbalance may change at different power levels. At threshold I am more 50/50. At easy efforts, I tend to be right dominant.
- Contact Favero support. They can do remote diagnostics. They were amazing with me and it turned out to be the washer issue above
- You can place a weight on the Favero and check calibration

Nope.

My single-sided Faveros are ANNOYINGLY precise (reproducible). Like literally down to the watt. I wish it would vary upwards, but nope!

It's so precise that I bought two singles for two bikes.

I also suspect they are highly accurate, as I cannot tell the difference when I swap between the two Assiomas I have. I was expecting some wattage differential but nope, also annoyingly similar down to the watt.

I've done several FTP tests on Zwift where I'm not tracking the power target as I ride and not in erg mode, and my Assiomas again - like literally down to the watt.

A 10% watt variation is totally unrealistic in my usage on Faveros with SS. Even 5% is totally unrealistic. If there's any watt variation for me, it's definitely <5%.

If I had a 5% wattage upward variation in my FTP tests, which would be around 10 watts at my FTP, I'd be cheering hallelujah!! If I were seeing +10 and -10 for identical efforts on FTP tests and all my other rides, I'd be calling my Favero SS unusable. Clearly that's not remotely the case.

@OP - You might be having some smart trainer power drift as the unit warm up or cools down, but I'm just extrapolating from my experience with the highly regarded 1st gen Kickr, which while every review says is 95% accurate, for sure has power drift for me as it warms up over the course of an hour. I can literally feel it, as at the start of my ride, the Kickr might say 200watts and it feels definitely too easy for me, then I look at my Faveros which I always run at the same time, and it's reading 170-180watts. For mine, it takes about an hour of riding (unfortunately) for that gap to close or get really small. So I end up always recording my (lower) Assioma power rather than the Kickr power, as it feels more correct to me.

I suspect quite a few other (?most) smart trainers have similar problems to lesser degree, even the top-rated ones; people are amazingly silent about discussing it, probably because they're seeing it too and afraid to acknowledge that there are difference between their smart trainer and their separate powermeters after dropping so much money on them.

Have you tested against a dual sided power meter / crank based / accurate trainer?

I used precision, when I should’ve said accuracy.

For example ... I’ve seen when folks sprint they typically have higher degrees of power imbalance than steady state efforts, and then that’s slightly more imbalanced than a noodle pace

So if on sprints you’re 54/46 and then steady state you’re 50/50... any extrapolation or power curve will be off

Yah?

You are OK in your use of terms.

• Precision = ability to recreate consistent results (even if the results are incorrect). If you have a consistent power balance, a single sided PM could be precise, but still inaccurate.
• Trueness = ability to report close to the actual value. If you have a variable power balance, a single-sided PM could be true but inacurcate.
• Accuracy = combination of Precision and Trueness. Unless you have both a 50-50 power balance that never changes during the course of a workout, only a dual-sided PM can be accurate (both True and Precise).

A single sided PM may be Accurate (or perceived to be accurate) for some. But they are not for the general population.

My Kickr 1 by most reviewers including DCRainmaker is 95+% accurate. It lines up extremely well with both my duos when it is warmed up as I mentioned,

As for accuracy, it's hard for me to believe my accuracy is off when all 3 separate devices line up nearly identically (and the Faveros to the freaking watt!). Having multiple devices that read the same is a pretty good sign of accuracy.

There is no way at all that my Unos are more than 10 watts off in precision (5%). I would notice that immediately. To even get a +5 watt increase in my ride averages requires a noticeable increase in average effort, every time. And for FTP tests, it's literally down to the watt. 1-2 at most. As said, I wish it would from time to time give me +5 on that FTP just to make me feel better, but nope. Literally +/- 1, MAYBE +/-2, but that's it. +5 FTP is like hallelujah land for me, really!

I’m envious of you!! :)

Don't be envious when gaining a paltry 5 watts is so freaking hard for me nowdays.

It's sad when I read some of those aero testing sites and see that I might be able to equal the wattage gain from a whole block of hard training by just moving my water bottle from the lower frame to BTA =

That said, while I'm far from a speedster on the bike, I've gotten to the point of diminishing training returns such that I really notice aerodynamic changes despite insisting to myself over the past 7 years that as a front of MOPer, that training >> aero for me. I've learned the hard way that at least where I've gotten to myself now on the bike, aero speed gains can exceed my training gains. Road vs TT bike is like 4 minutes/hr. Add race wheels, another 2 min/hr. Add TT helmet, another 1 min/hr. Change from regular bike jersey to tight trisuit, another 1 min. (Put on not-that-flappy cold weather jacket, slow by 1min/hr).

Put all those together and I'll need over 40 watts of training to account for that gap between aero-TT vs road-bike nonoptimized.

I've got a new bike coming soon which should get me better aero position and I have yet to try latex tubes on race day, but that's next.

I only trust power meters I can perform a static torque or force check on (and preferably adjust)...or can compare against one that has been checked...and that measure the contributions of both legs.

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http://bikeblather.blogspot.com/

As others have said, you might expect a small amount of variation due to using one-sided Assioma. You might also expect a small difference when comparing measurements at the crank/pedals vs the trainer due to drivetrain losses, but your results are the wrong way around for that.

As each source of power is being reported into a different "head unit" could there be anything going on there? Not counting zeros, "smart" reporting intervals vs every second, averaging etc?

Cheers,
Rich.

"Konnen sie die uberprufen, Herr Anhalt?"

"9."

Natürlich

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http://bikeblather.blogspot.com/

I find my trainer reads ~10% lower than my quarq power meters on 2 of my bikes. I gave up on having them match. They are both consistent which is more important. An increase in FTP with one power meter is also an increase in FTP with the other. That's more important to me than the absolute number.

Are you running some kind of training software to control your trainer? Many programs allow for you to control the trainer based on your power meter numbers, that way it wont matter how much they differ. I prefer to train to the quarq numbers since I also will race with the quarq.

+1 here. I rarely use the Neo for any power feed - relying on the quarq instead. I have compared the two, and the use of the quarq is the one that made a lot more sense to me for several reasons when considering the bigger picture of what I was attempting to achieve from training.

However, that gap between the averages is on the upper side of what I think would be expected, even taking into account one sided imbalance at 'tick over' and low power precision of tacx trainer power estimates. (OP: If you were in the big ring for this test at power that low I'd say this is a likely issue.)

As sad above, if you want to understand this then you'll need to do some work yourself, and potentially share some details/files. Twin recorded structured workout with some defined power intervals done in varying gear combinations is going to give you the answer in most cases, although at some point you may also need to run a dual sided powermeter against the trainer too.

Some bad advice so far. Running a bunch of tests to compare the two is a waste of time. The only way you are going to know what is going on is to compare your devices to known accurate power meters. That would require you to have a friend who is very accommodating about loaning equipment and has the necessary knowledge to understand if their devices are actually accurate. Then you could, say, compare the pedals to a powertap or crank based power meter, or borrow known accurate pedals and compare them to the Flux. The likelihood you can arrange all of that is probably not very high.

In my household we are two for two for one-sided power providing junk data, as found from testing a Stages that came with a second hand bike. We've had good consistency between three Quarqs, a set of Assioma Duos, and a Saris H3. Also providing junk numbers is a Wahoo Snap trainer. Your Flux might be accurate or it might not be, depending on when it was manufactured and some luck of the draw.

Personally, if I was you, I'd just bite the bullet and upgrade to Duos. Then use them as your trusted power meter. If the trainer doesn't match, use the pedals as your power source on the trainer.

"The only way you are going to know what is going on is to compare your devices to known accurate power meters." my question to you is how would one actually determine accuracy? In some fields there is such a thing as a certified standard against which one can compare a device reading to determine accuracy, but in bicycle power meters everything I have ever seen is by inference. What I mean by that is for instance you hang a known (and presumably accurate or standardized reference) weight/ mass from the pedal and then calibrate the force gauge. That still does not guarantee accuracy, because the power you read is a calculation of a bunch of input numbers and also depends upon the temperature coefficient of things such as the strain gauge etc.... accuracy in power meters seems to be a tough nut to crack.

For the situation above you are suggesting a comparison and assume that at least if 2 agree then that is the best you can say. Neither can be said to be accurate, just that at least they are the same or in agreement.

The problem that the OP is facing is which of the two results he wants to believe. From a training point of view precision is most important and therefore if he uses the bike power meter outside then uses it also inside to calculate the power he is producing at least it is apples and apples. Whether the trainer is the same makes very little difference once you decide to believe the bike power meter and as pointed out you can in many programs use the bike power meter to power match likely for this very reason. As for single or dual sided that horse has been beaten to death.

@OP

Easy, correct answer here:

Just trust and use the Favero Uno powermeter numbers. They are 100% legit. Sure, you may get some L/R variance, but there is literally nobody on this form with hard numbers showing wide uno variation in practice, nor are there any of the (thousands) of users like myself that see such variance (like 10+ watts) on rides that we do literally every week, for months straight.

The Favero is an extremely respected and well regarded unit, AND it will be what you will be using on race day to target and measure power.

Just use the Favero. -endthread

Not true. As I described above, IF you can actually check the accuracy of the static torque or force reading (and, ideally, "tweak" it), then you've just taken care of the largest contributor to power meter inaccuracy. Accurately reading rotational velocity is pretty trivial, and most PMs do a good job of that.

So, doing a torque slope calibration (i.e. NOT just an offset zeroing, which is what head units call "calibration"...sigh) on, let's say, a Quarq, an SRM, or a PT hub, is going to give you an accurately reading PM. I've been told some PM pedals also allow for a force check, but I haven't done that sort of check myself yet, so I can't really say how well (or not) that works.

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http://bikeblather.blogspot.com/

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

Fwiw….

Some folks have the roadie habit of backpedalling at stops to align the crank to start again. Cannot do that in an aero test with a Quarq. That engages the on the fly zero at that time. Apparently this can be disabled via the app so only GPS manual zero is used.

If unlucky enough it is possible to do this and barely not violate the zeroing error check and your foot is light enough on the pedal and suddenly you’re at 25mph and reading 100w.

I had a support ticket with Quarq blame what I saw on a ride with that and also the battery cage spider needing the legs bent more. That all resolved that.

I thought you could change the slope in their app? At least they claim so:
https://www.power2max.com/en/2017/07/power2max-app/


I have the 1st generation P2M (going on 10 years and likely 100,000+ km in all kinds of weather!) and can static torque test it, but not change the slope. Seems like with at least NG and NGeco you should be able to do that so you have whatever you need on that front.

This is what pissed me off this week.

You can set a %. So you can say "report 98%". But you can't measure off a hanging weight so not sure what you would scale this off

My conversation with them went like this

me : hi, can i do a static torque test ?
them: you don't want to do that, here is an article on how we calibrate
me: fine, however it is reading 10watts higher than my other PMs and I'd like to get to the bottom of it
them : your other PMs are probably wrong but if you want you can knocks 10 watts off by using a %.

I was told I could pay 50Euro to be able to display a torque value on wahoo, not a garmin but I would be disappointed with it.....so not sure what to think.

In the paperwork with my P2M came a slope value that defined how much each ZO unit was in Nm. Using that you could do a static calibration just using the ZO value with and without applied weight (like you can on e.g. SRM and Quarq). I can't tell you if it works like that on newer units, but that's how it works on mine.

Yes I remember the good old days with my Quarq.

Today I do a static calib, get a 47. Hang a weight, do a calib, get an error :-)

I'd be more than happy to be wrong

Had no idea we could do this. Three Wahoo kicker and all three read 10 watts higher than my P2M. Explains my faster bike splits on lower wattage. I'll have to check into it.

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http://www.sfuelsgolonger.com

You need smaller weights so you can slowly build up the torque to trick it ;p

Does your device auto-zero when you don't pedal ?

Yes

I have the same setup

Tacx Flux and Assioma, both single and double, I also have a Rotor INpower and a Quarq and a Stages

I dual record most of my races on Zwift and have an extensive log of how different power meters compare.

All of my pedal and crank power meters are within +/- 2%. You get more variation at peak power, +/- 10% for 1s peak, Assioma and Rotor seems to read highest. however, after about 15s differences are minimal

This brings me to the Tacx Flux. It doesn't actually have a power meter in it, it is a calculated power based on the power input to the magnets, Tacx and Wahoo use this mechanism, while Elite trainers actually contain a strain guage. The Tacx It is incredibly sensitive to when you calibrate, It needs a good 20min warm up before you calibrate, otherwise you get odd readings. Also, below 150w the Tacx reads significantly higher than Assioma, 180-300w it is pretty much bang on, 300w+ the assiomas read higher.

In a typical Zwift race, like a time trial, where I am averaging around 340w the Tacx is about 3-4% down on the Assioma, however, a newly waxed chain and a squirt of silicon lube on the belt on the Tacx brings it down to about 1% lower

Spot on. In addition to my Tacx Flux, I have a Tacx Neo 2T, which is supposed to be one of the best trainers on the market. When I first had it the accuracy was within 1% of my assiomas; all of the reviews raved about it. However, over the course of 2 years it has gradually got less and less accurate, currently it reads 6-7% below my Assiomas (Uno and Duo), and Rotor and Quarq. As there is no way to calibrate a Neo 2T I am stuck. Therefore when I race on Zwift and need to dual record I am back to my Flux as it is generally pretty close, as long as I warm it up properly and keep it well lubed.

Lots of people race on Zwift with their Power Meters as primary. Lots of people on this thread saying the same, ride indoors on same PM as you ride outdoors, I get it..... however, if you are close to winning races, then anyone who races with PM as primary is immediately suspected by their competitors, it's a really simple job to add 10mm to your crank length with an Assioma or Garmin Vector. You can change the slope on a Rotor, I guess you can do something to a Stages or Quarq. However, its much more difficult to frig the readings on a trainer.

Agreed. I have my kickr connected to TR and that's it. I use the numbers from my single Favero to Garmin 830 because that's what I will be racing with. Usually the kickr and favero are about 20 watts off and I calibrate every session.

The attached screenshot shows a dual recording last night with the Tacx Flux connected to Zwift and Assioma Duo connected to my Garmin. The chain was newly waxed and trainer recently serviced.

Over 20mins the difference is just 2% which is about right for drivetrain loss, however, short hard intervals of 1 minute or less the Tacx reads in excess of 6% low. This is fine for most people most of the time, but a disaster if you are e-racing and contesting the sprints