Just sharing some personal experience with reference to left sided Stages power meter for info. I have been a long time user of Quarq spider PMs and have them on all my bikes… until recently when my trusty Quarq Riken (9 years old) finally died on my TT bike. Thinking I was going to get a new TT bike soon I went for a quick and dirty ‘fix’ and got a left sided stages. Quarq are dual sided and I have Dzeroes on the other bikes. I am 46/54 or 47/53 right side dominant. Stages takes left sided and multiplies x 2. My conclusion after 2 weeks was that it’s a total waste of time IF you are mixing PMs. My smart trainer and other Dzeroes are well within tolerance but the Stages is miles out (lower). So much so, it’s coming off and being replaced. Nothing wrong with the Stages approach if you are using them and them alone, but they sure don’t seem to present accurate data under these circumstances. Be interested to hear of other experiences. Sharing is caring etc etc.
With left-sided 4iiii you can adjust the multiplier to compensate which works OK most of the time. Seems odd if Stages don’t do that since it’s an easy software fix. There are discrepancies in all of them, so best to stick to a single brand.
I heard stages is inaccurate no matter what
Do any of them do this? It’s not something I’ve ever looked into
I guess giving GCN a tour is a start but I’d rather have an independent body with standards that they all follow. Without that we’re dependent upon the word of the companies selling the product to tell us they’re accurate. Not exactly objective.
But for me, it’s not the biggest issue. I train on a Kickr bike for that most part and have my stages left PM on my gravel bike and it seems accurate enough. I used to have Assioma pedals but never used them on my gravel bike so sold them. But I’m not too concerned with my stages pm if it’s a little inaccurate. I’d notice if it was 50watts off.
it is not about the tour. Check out the machine they got built and the claim of dynamically calibrating “every” single unit. That is a huge difference to a single point static torque test.
Matching others isn’t really a good test. Consumers can do their own dynamic check but it’s a PITA so hardly anyone does it (unless they’re really really desperate).
Dunno about that inaccuracy. I have Stages on 3 bikes, Garmin on 1 and train Wahoo Kickr and Stages trainer at gym. All seem close 'nuf. How accurate do you really have to be? Seems a relative thing.
I did a hill test once.
I had three PMs on my bike. I rode up a hill I knew the distance and elevation. I knew my weight and bike weight. And used a calculator to estimate the workload. Then I rode up the hill and compared the results.
That’s a free dynamic test. You only need one power meter to conduct this test. No need to compare two or more.
Power2Max gives instructions: Accuracy – Power2Max North America
I’m a stages guy.
My PM history has been 2x cyclops rear hub, 3 stages left side, and a cyclops hammer (smart trainer).
All my stages have been consistently accurate (I have them on 3 bikes right now).
Riding my stages on the trainer with the hammer and stages hooked up to different head units gives accurate readings. The stages tracks like 10w lower at lower power (>300w), and tracks higher by a similar amount at high power (500w+). So it’s non-linear and depends on the wattage. I had this in a spreadsheet a while back.
I did not have a noticeable change in power numbers when I had my original switch from the rear hub cyclops to a left only stages.
Maybe I’m more balanced? You might consider contacting stages warranty and try to get a new one. If mine is reading low, maybe I should think about going pro! Lol
@GarageLab gave the right answer. You don’t need a 6 figure test rig. You don’t even need a hill, but whether you have a hill or not, in order to get accuracy and precision it’s a PITA so hardly anyone does it. Climbing the hill at different speeds allows you to validate across the entire range of power, cadence, and crank torque.
I appreciate your opinion, however I disagree. Just because you don’t believe this can be done with some degree of precision doesn’t mean it can’t be done. As Robert so truly stated, it’s a PITA to conduct.
The hill test is a field test that can be used to validate your device. This isn’t Strava guessing many of parameters. Ideally you do this on a no wind day on a good surface with little traffic and eliminate/control as many variables as best as possible. It’s a PITA to do.
Same with field aero testing. It works but it’s a PITA to do.
Same here. 3x Stages L crank and one P2Max. They are a guide for me, not a piece of metrology equipment where I’m measuring hundredths of a micro inch for silicon wafer fabrication.
Single crank is always going to be less complete info than dual, a spider or pedals.
Exactly. On those occasions when we have done the PITA controls and protocols, we validated not against an online calculator but against a full power dissipation model, then altered drag by a known amount to see whether we could capture that accurately. Drag can be altered by a known amount either by adding objects like spheres of known size and measuring the change in CdA or adding objects of known weight and measuring the change in rolling resistance.
The point is, you don’t need a $100,000 test rig, and you don’t have to settle for “two out of three” comparisons against other power meters. You do have to be willing to do PITA tests.
As an historical aside, VE and modern ways of estimating CdA from field tests were a side effect of trying to come up with a way to do dynamic testing of on-bike power meters.
I’m not trying to make you a believer, but a simplified calculation is very good. See pg. 14 of this PDF. Maybe you’ve seen it?
http://anonymous.coward.free.fr/wattage/cda/indirect-cda.pdf
Again, I disagree.
I think we are viewing this from two different places. I’ve been collecting field data (for work) for more than 2 decades for use in design. I like models. I’ve come up with my own. They’re useful, especially when you don’t have a lot of budget to do all the field testing you want to do.
No biggie…if you ever buy a dyno, let me know and I’ll send you my PMs to check. 
Okay. It’s a benchmark. Used consistently it gives me info that I make use of (or don’t).
Yes yes yes!!! I’ve had Stages for years (multiple left-side on multiple bikes). This year…they all read low compared to my other power meter(s): Assioma (duo) & Tacx smart trainer. I’m 45/55 (l/r). It’s a huge difference in target power.
I know I should do PowerMatch, but that’s not consistent either with the different bikes/sensors. I need to pick ONE, I know.
Bottom line: stages reads low
In my experience, the key problem with left right imbalance was that it changed based on intensity/fatigue/focus so simply scaling the pm (4iiii left) didn’t work.
I found the same thing, I am right leg dominant, have a few Quarqs and used to have a Stages, I also had some PowerTap P1 pedals. The Quarqs and pedals were always pretty consistent, the Stages always seemed to read low (made sense).
I took the battery out of the RHS P1, effectively turning the pedal into a LHS only PM, and found similar results. Now the Stages and P1 were close and the Quarqs read high.
Ultimately it doesn’t matter to me whether one or the other is more/less accurate, all that matters is that they are consistent. So I sold the Stages, and now have 3 consistent power meters.
Of course a single sided PM is not going to be as accurate as a dual sided. Does anyone expect otherwise? I am pretty well balanced, but even so, I am sometimes 51/49, sometimes 49/51. A left only measurement inherently has more uncorrectable variations in measurement than a dual sided measurement. That’s why I stopped bothering with single sided power meters (of any brand)