Shimano Based Crankset Power Meters: Not As Accurate As You Might Think

This report presents clear evidence, based on robust data, that power readings derived from dual sided cycling power meters using Shimano cranks, does not provide consistent levels of accuracy as specified by power meter manufacturers.


The Shimano alloy crankset is a popular base unit for a number of companies to use for their power meter products. Not originally designed as a power meter, electronics engineers successfully mounted strain gauges on the left side crank only (where power was doubled) to give cyclists a more cost effective way of measuring their power output.

Stages Cycling was the first company to develop left-crank based power, applying strain gauges to the crank arm. Stages Cycling – Wikipedia 

Following the success of Shimano based left-only power meter products almost every company started offering a dual sided power meter configuration by placing strain gauges on the corresponding right side crank arm.

From a consumer perspective this was welcomed. A somewhat cost effective (“somewhat” as it’s not as cheap as a left-only offering) dual sided power meter, independently measuring left and right power, and reporting metrics such as pedal balance and true total power output. 

From an engineering perspective the right side Shimano crank power meter has been a challenge. The design and shape of the right crank is very different from the left, and with Shimano changing the shape from the FC6800/FC7900 with the R8000 and R9100 right side cranks for a wider four arm arm/spider interface, things became even more challenging for them to obtain accurate power (torque) measurements from. There has been mention of a strain gauge redesign required specifically for the R8000 & R9100 right side cranks.


Over the past year I’ve ridden and compared power readings from ELEVEN (11) Shimano R8000/R9100 cranksets from seven companies. I’ve had other riders perform the same testing protocols on a number of these units. Based on the data from these tests, and confirmation of these results from independent electronic engineers who are familiar with cycling power meters – I do not believe the power measurement from any Shimano R8000 or R9100 RIGHT side cranks is at an acceptable level for consumers to confidently rely on at this point in time.

I have been in direct communication with a number of the companies mentioned in this report over the last 12 months.

None of these companies have questioned my testing protocol, or results for what would be considered successful tests of left-only power meters and their non Shimano dual sided power meters.

Each company has been provided this report and all data collected on thier power meters in advance for response.   

My goal here is to identify issues consumers may encounter themselves with these products. I hope these findings will lead to more accurate power meters on the market.

Background

Strain gauges are a solved problem. The gauges used today are reliable and dependable. Other power meter features are of a high standard: Battery life. ANT+ & Bluetooth Smart data transmission. Active Temperature Compensation (to an extent). If this wasn’t the case the power meter industry would be in trouble.
 
Digital cadence sensors are also typically accurate enough to obtain quality power output from. (Accurate cadence is required for accurate power from these power meters). Some power meters still rely on magnets for better cadence readings (which are more responsive in my experience). Accurate cadence readings are a part of this bigger picture discussion, but they’re not the main show in this report.

Why are power meters so hard to get right? 

Bicycle power meters are effectively a moving weight scale. Standing on a bathroom weight scale requires you to be stationary for accurate results. Power meters require the same accuracy moving at high speed (rotation, vibrations, etc), while measuring multiple force vectors, in almost all environmental conditions imaginable.

Shimano Cranksets as Power Meters

Shimano produce cranksets, not power meters. Converting these cranksets into power meters is a post-production process where strain gauges are typically placed on the external surface of the crank arms.

Shimano use the same post-production strain gauge placement design as third parties for their DuraAce R9100P Power Meter. However when Shimano themselves can’t produce a quality industry leading power meter from their own cranks from day one – there’s a problem. A big problem. 

References:
– DCRainmaker DA9100P Review: Issues with left/right accuracy.
– Bike Radar DA9100P Review (Ben Delaney): Issues with left/right accuracy.
– GPLama DA9100P Review : Issues with left/right accuracy.

Discussions with a power meter designer/engineer Keith Wakeham on the topic of using Shimano cranksets as power meters has confirmed there are difficulties with design asymmetry, chainring positional affinity, and the coupling effect when using strain gauges on the RIGHT side crank arm of a Shimano crank. This is a known problem that isn’t limited to just the drive side, however it’s where the issues arise when using a DUAL sided Shimano based power meter.

Inside Shimano HOLLOWTECH Cranks

Internals of a FC-R6800 RIGHT Hollowtech crank.
Photo Source: https://www.mobile01.com/topicdetail.php?f=316&t=4849613

Internals of a FC-9000 RIGHT Hollowtech crank.
Photo Source: https://www.mobile01.com/topicdetail.php?f=316&t=4849613

Onto the testing…


The Lama Lab Test Protocol: 

My “Lama Lab” test protocol has shown to provide quality results when testing both power meter and smart trainer power measurement. It’s by all means not perfect, however it has successfully identified issues that have been acknowledged (and in some cases resolved) by power meter and smart trainer manufacturers.

This protocol uses a combination of SIM (Simulation) and ERG mode. ERG mode forces you to pedal at the set target wattage. For more details on ERG mode I have a 12 minute video explaining ERG over YouTube: ERG Mode Explained.

– Power meters stationary in the room for at least 10 minutes (temperature adjustment)
– Data recording on Garmin Edge or Wahoo Elemnt units (using the same vendor for all meters if possible). 
– 1 second record interval. GPS disabled. Units placed <1m from power source.
– Clean chain (<0.75% wear). Clean Cassette.
– Straight Chainline selected (36/39 17-18) for ERG.
– Zero-offset performed on all units (as applicable) at 0 minutes.
– 10 minute ride (SIM mode / Human warm-up / a few short hard efforts).
– Dismount bike. Zero-offset performed on all units / Spindown on trainer (if applicable).
– 10 minute steady-state ERG @200W ~88-95rpm. Both hands on bars. Natural/smooth pedalling. 
– 10 minute steady-state ERG @250W ~88-95rpm. As above. Balanced, smooth, natural pedalling.
– Maximal sprint of 5-8sec. Out of saddle.  (SIM or Level mode).
– 4 minutes easy spin (SIM or Level mode). 
– Over/Under Intervals in ERG each of 20 seconds: 150W/350W/150W/350W/150W/450W/150W/450W/150W. Balanced, smooth, natural pedalling through these intervals. 
– Cool-down. Sometimes involving a harder 350W/400W effort for ~60 seconds in SIM to collect more data. 
– All data (FIT format) labelled according to equipment used and uploaded to DCR Analyser.


Shimano Based Power Meter Cranks: LEFT ONLY

Data shows left-only Shimano based power meter cranks typically report power within their specified accuracy specification (+/-%).  I have encountered some left side cranks reporting lower than expected power measurements. In some instances this has been resolved with re-installation and correct torque on the pinch bolds (14Nm – max specified by Shimano). I have had left-only cranks from manufacturers not listed in this report that have zero-offset stabilisation issues and power fluctuations. So they’re not immune to issues either.

The caveat with LEFT only is with the doubling of power from one side. It assumes 50/50 balance for the unit to show “correct” output. Small lag in power reporting due to no measurement on right side. 

In short – Data collected on LEFT only Shimano crank power meters appears mostly accurate. This report focuses on the RIGHT side crank arm.

References:
Stages Power Meter (Single/Gen III) – Install, Ride, Data Review
Magene RIDGE Shimano Ultegra R8000 Power Meter: Details // Install // Data Review
XCadey X-Power Budget Power Meter: Unboxing, Install, Review

Shimano Based Power Meter Cranks: RIGHT / DUAL SIDED

Here’s where things get tricky.

Shimano Cranks Tested (11):  

– Stages LR (x2) 
DuraAce R9100 (Gen 3) 1st Unit
DuraAce R9100 (Gen 3) 2nd Unit

– Pioneer (x3)
DuraAce R9100 (SGY-PM910H ANT+ only model) 
DuraAce R9100 (SGY-PM930H ANT+/BLE model) 1st Unit
DuraAce R9100 (SGY-PM930H ANT+/BLE model) 2nd Unit

– 4iiii (x2)
DuraAce R9100 (PRECISION PRO) 
Ultegra R8000 (PRECISION PRO)

– Giant 
Ultegra R8000 (Power Pro MY19) 

– Shimano 
DuraAce R9100-P 

– WatTeam PowerBeat
Ultegra R8000 G3 (*Gauge placement different to the others) 

– XCadey 2XPower
Ultegra R8000

Method: 
Lama Lab Test as documented above and here: GPLama How To: Comparing Power Meters // Power Accuracy Testing // DCR Analyzer Tool: https://www.youtube.com/watch?v=JhheDLXRM7I

The Results: 


Steady-State 250W ERG  

Power Meter: Crankset used
ERG: 50% of 250W ERG Mode (125W)
Other: Right side power channel of non Shimano Crank (Assioma/P1/Vector3)
Right: Shimano RIGHT side reading

Power MeterERGOtherDiff %RIGHTDiff %
Stages RIGHT DuraAce R9100 (Gen 3) 1st125124.14-0.69116.74-6.61
Stages RIGHT DuraAce R9100 (Gen 3) 2nd125121.04-3.17116.16-7.07
Pioneer RIGHT DuraAce R9100 (SGY-PM910H)125123.09-1.53112.6-9.92
Pioneer RIGHT DuraAce R9100 (SGY-PM930H) 1st125127.872.30114.76-8.19
Pioneer RIGHT DuraAce R9100 (SGY-PM930H) 2nd125122.79-1.77116.91-6.47
4iiii DuraAce RIGHT R9100 (PRECISION PRO (Dr.SLane Data))125123.18-1.46114.44-8.45
4iiii DuraAce RIGHT R9100 (PRECISION PRO )125123.15-1.48114.16-8.67
4iiii Ultegra RIGHT R8000 (PRECISION PRO)125123.36-1.31113.95-8.84
WatTeam R8000 G3 RIGHT125124.06-0.75117.71-5.83
Shimano DuraAce RIGHT R9100-P125125.670.54115.12-7.90
Giant Ultegra RIGHT R8000 (Power Pro MY19)125122.83-1.74120.27-3.78
XCadey 2XPower R8000125125.310.25109.44-12.45
Average125W123.74W0.90%115.19W7.85%


– Variance higher at 350W & 450W ERG.

– Differences not as pronounced in random terrain SIM mode or riding outside. 

– Harder steady-state efforts indoors (SIM) and outdoors does reproduce this issue. 


Isn’t this just drivetrain loss?

No. The discrepancy in power readings is between the pedal power meter and crank power meter which are directly connected. The power differences reported are more apparent on the RIGHT side. The controlling smart trainer in ERG also provides a tertiary power comparison source.

What did I compare against? 

Multiple sources:
– Favero Assioma DUO (Dual sided pedal power meter. ±1% Accuracy) 
– PowerTap P1 & P2  (Dual sided pedal power meter ± 1.5%) 
– Garmin Vector 3  (Dual sided pedal power meter ±1% Accuracy) 
– Tacx Neo / Neo 2 (Direct Drive Smart Trainers ±1% Accuracy) 
– Wahoo Kickr / Kickr CORE (Direct Drive Smart Trainers ±2% Accuracy) 

Basic Formula:
Dual Sided Power Meter L + R = Smart Trainer Power ≠  Shimano Crank Power Meter Total Power.

eg. AssiomaDUO Power = Tacx Neo Power ≠ Shimano Crank Power. 

More specifically indoors and out: Power Meter R ≠ Shimano Right Crank Power.

Note: This doesn’t factor in any specific mechanical losses incurred between the pedal and crank, and drivetrain losses at the smart trainer power measurement point (effectively the rear hub). However, measured losses are never greater than a few watts (<2%) of TOTAL power using a clean drivetrain when cross-chaining using 52/28. Reported power from the RIGHT cranks is up to 10% different, on one side alone.

I can not attribute the differences recorded to mechanical or drivetrain losses.

Why hasn’t this been detected / reported / resolved? 

Comparative testing of consumer power meters isn’t commonly performed. Not typically to the level of detail (and cost) that it has taken me to reach my current conclusions. 

The independent testing of Shimano R9100 LR cranks at the University of Colorado Boulder commissioned by 4iiii on three of their cranks was based on a steady-state riding protocol on a treadmill (not ERG). With their comparison being calculated wattage, not other power meters, and using two minute intervals at lower cadence ranges than I would expect a trained cyclist to ride (only up to 85rpm). Their summary result of 1.58% accuracy was an average across all data sets with the three Shimano R9100 cranks tested.

There was datapoint at ~250W (calculated) reporting as ~240W. Indicating there is outlying data points. 240W @250W calculated is -3.70% equating to -9.7W. What wasn’t reported was the Left/Right power figures on any of these data sets. Yes, I’m being selective here – my point being we need to know more detail as to why that data was out by that much.

On the upside to the testing in Boulder, their results with non Shimano cranks using their strain gauge technology were a LOT better. With the carbon SRAM XX1 crank achieving 0.84% accuracy on average across four cranks tested. Indicating the gauges and technology used by 4iiii is of a high standard that will produce accurate measurements assuming the base crank it is installed on doesn’t suffer from the same problems as the Shimano RIGHT crank design.

Performing the Lama Lab Test protocol on the dual sided FSA SL-K crankset fitted with 4iiii power meter gauges reported no issue with left or right side power readings.

Why haven’t other media and reviewers reported this?

I’ve not seen any reports showing the same testing as what I use in the Lama Lab (as documented above). Specifically longer duration smooth pedalling steady-state ERG efforts in addition to over/under intervals – Tested against a long-term known-good power sources – Which I consider the AssiomaDUO / Tacx NEO / PowerTap P1 to be.

I have discussed this issue in a number of reviews already. In particular the Shimano R9100P, my WatTeam G3 review (results confirmed by WatTeam engineers), and in my Stages LR video. This isn’t ‘new’ news.  

This is also difficult to diagnose. It requires multiple power measurements on the same bike at the same time. Not many cyclists will install two independent L/R power meters on their bike. Even less will perform any in-depth analysis of the data. A growing number of cyclists are comparing their bike power meters to their smart trainers and are reporting power differences. This issue could very well provide answers to some of those queries.

More often than not when users ask questions regarding power meter discrepancies in a public forum they are dismissed as ‘drivetrain loss’ or L/R imbalances. Unfortunately these reasons are echoed by some manufacturers without performing a full analysis of each issue. This is not a drivetrain or a rider L/R imbalance issue.


What exactly is the issue and why hasn’t this been resolved in firmware, or with better strain gauges?

The engineering complexities of this problem is best explained by someone who can cover this in the technical detail it deserves. And that person is Keith Wakeham. Keith is one of the original designers of the 4iiii power meters. Keith is listed on the patent under ‘Inventor’. He really knows his stuff. Reference: https://patents.google.com/patent/WO2016030768A2

Keith has a blog over on https://titanlab.co and has put together a post on this very topic: https://titanlab.co/shimano-crank-design-blunder/

If you have a few minutes to keep diving into this issue to the depths you never thought possible – Grab yourself a coffee and watch his video here:

This isn’t an incorrect slope or miscalibration issue. It’s much deeper and harder to solve given the design of the Shimano RIGHT crank arm/spider

For now this issue exists even with the latest meters with the latest firmware.

Team Sky / Pro Team X / Mine Reads Fine

Professional teams are sometimes provided non commercially available product. Teams are paid to use equipment (read between the lines here of what they’ll say about said product). Professional teams are also unlikely to perform any power comparison tests to the level required.

“Mine is accurate”. Compared to….? What was your testing protocol? How was the data recorded and analysed? The answer here is typically “we’ll need more data”. Beware. Getting to the answer is a rabbit hole of indeterminate depth.

My Take Outs….


Shimano based dual sided power meters report lower total power in my tests due to inaccurate measurement of power on the right side in a number of pedalling scenarios. This is particularly evident in steady-state smooth pedalling efforts across a range of wattages.

At this point I am not confident to use ANY Shimano based dual sided power meter crankset as a baseline to compare power readings from other power meters or smart trainers.


I own a Shimano based dual sided power meter as referenced above. Does this matter? 

Yes:
– If you’re using the reported L/R balance values as part of your training.
– If you’re comparing multiple power sources.
– If you have more than one type of power meter (One that’s Shimano based, and one that is not).

No:
– You’re not bothered with L/R balance. 
– The power meter is your ONE source of power for all training.
– You have more than one of these Shimano crankset power meters.
– You’re not worried about a few % margin of error with your real power output (and metrics that are slightly skewed because of this) 

Company Responses… and where to from here.

All in all I’ve welcomed the discussion this report has lead to with most of the companies named. There is obvious (and admitted) complexities with the Shimano RIGHT crank design when used as a power meter. 

I understand it’s not in the interests for any of these companies to admit any major shortcomings of their products. What I’m looking for is a sound explanation as to why these discrepancies have been narrowed down specifically to Shimano RIGHT cranks – why I’m not able to use any of them as a reliable baseline of power comparisons – and most importantly – is there a possible fix for this?

Shimano Australia:
– Stand behind their ±2% accuracy claims of LEFT and RIGHT Shimano Power Cranks.
– Discrepancies in my provided RIGHT power data due to bugs in the firmware I used.
– I tested the R9100-P with 4.0.7 (March 2018) which is the firmware that their changelog indicates resolves accuracy issues.
– It was recommended I update to 4.1.7 (Feb 2019) and retest.
– I raised concerns that 4.1.7 change log lists no updates to power accuracy. Also infers they had an inaccurate power meter on the market up until February 2019…!?

My Action Points: Source another R9100-P and retest with 4.1.7.

4iiii Innovations: 
– Acknowledged issues with the Shimano crank asymmetry and non-uniform coupling effects.
– They believe their firmware and calibration protocols are robust enough to stand by their accuracy claims. 
– My riding style given as a possible reason for the discrepancies seen in ERG. (This doesn’t explain why my riding style wasn’t a problem with their non Shimino L/R crank in the Lama Lab tests, or Dr. S.Lane also recording the same lower power measurements with the Shimano based RIGHT crank). 

My Action Points: Continue working with 4iiii to provide more data from the Lama Lab and in person across more of their power cranksets (Both Shimano and non Shimano). Ongoing.

Stages Cycling:
– Stages stand behind the accuracy and repeatability of the Stages Power R and Power L/R meters in the vast majority of use.
– They mention the loading of the spider and crank is different during the pedal stroke in ERG as opposed to SIM or riding outside – which could be contributing to the discrepancies. 

My Action Points: Continue working with Stages to provide more data from the Lama Lab and in person across more of their power cranksets (Both Shimano and non Shimano). Ongoing.

Pioneer:
– Data analysis still in progress. TBA. 

Giant: 
– No response. TBA.

WattTeam: 
– No longer in business. RIP.

XCadey:
– Data analysis still in progress. TBA. 

Notes/References:

– In comparative power meter testing it is difficult to use the total ride/activity power as a measurement of accuracy due to factors such as start/stop delays across different power meters, possible data interruption (drop outs), etc, all impacting the overall total power recorded. This is why the focus of this report is specifically on 250W ERG steady-state efforts.

– The data from the Giant PowerPro has changed with recent firmware updates. From reading high on the right, to low, to a random point in between, sometimes. I suspect they are fudging or scaling the left/right to account for these issues. The dataset used here indicating LOW readings on the right was from fw237 (latest release as of testing).

DCR Analyser: Online tool for reviewing and comparing FIT file data. 

Shimano R9100-R Power Meter tested June 23rd 2018 with Firmware 4.0.7 released 27th March 2018 – “Update to make output value more accurate”

Technical Report:Accuracy Testing of 4iiii Innovations PRECISIONPowermeter Technology. Scott Cooper, Ph.D, 4iiii Innovations Inc. Wouter Hoogkramer, Ph.D and Rodger Kram, Ph.D, University of Colorado Boulder University of Colorado Boulder Locomotion Lab September 14, 2018

Patent US10060738B2 (United States) Adhesively coupled power-meter for measurement of force, torque, and power and associated methods Inventor: Kipling Fyfe, Keith Wakeham

Validity and Reliability of the PowerTap P1 Pedals Power MeterJ Sports Sci Med. 2018 Jun; 17(2): 305–311.

Categories: Power Meter, Uncategorized

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43 replies

  1. Brilliant research here mate. This seems like a pretty big issue. If power meters are claimed to be within 2% accuracy and they are upwards of 8% they are open to a large number of returned products.

    I was going to go crank based but not now. Cheers legend

  2. Yep, I’ave always thought the readings from my Shimano 9100 power meter were dodgy, this just confirms my intuition. I used to actually watch the readings on my old power meter but I take the readings on this Shimano Power Meter with a grain of salt.

  3. When did they know and Who knew? Is the question. These companies have been taking advantage of the consumer for years. These companies have been making tens of millions of dollars just hoping you didn’t notice. The companies in question all took part in a Greed campaign instead of facts. The industry has come along way in the past 10 years because of the willingness of dedicated consumers to embrace the science. The consumers and science have pushed the industry to where it is today! Consumers had an option for a better product but because of their cover-ups and misinformation we made a wrong decision. One last thing, when we spend $1,000 on a product. We are investing in you and expect and deserve respect.

  4. Hi Shane, I really enjoyed reading through this article. I’m wondering what’s the effect of this on total power accuracy? From your tests its clear that the right side isn’t measuring accurately. However, many of these units line up well with other power meter types in most of the tests Ray preformed (to the point Ray recommended the units as accurate and reliable). I’m trying to figure out how to interpret the idea that the right side meter is reading inaccurately, yet the total power appears to display within manufacture +/- specs. Is this issue addressable through a firmware update?

    • Total power is impacted. Total = L + R.

      I address total ride/activity power, other reviews, and the firmware question in the report.

      See Keith Wakeham’s video linked in the report for the engineering ‘why’ of this problem.

      In short – There’s a problem. A big problem.

      • Fwiw – I’ve actually only reviewed a two units with the impacted crank arms noted here (Stages LR & Shimano’s own solution). The remainder have been other units either prior to this set of crank arms, or just other crank arms or technologies altogether.

        The challenge is the lack of consistency. In my Stages LR test, I actually had pretty good results (and have for a while). Though, I’ve also seen some oddities here and there over the last 4-6 months that don’t make sense in isolation. In the Shimano power meter test, it was a complete mess. Oh, actually technically there was a third – WatTeam G3, which one might remember I saw issues that couldn’t be explained at the time that needed more investigation. Then they went under.

        I am in the midst of testing the latest 4iiii Shimano dual-sided units, and have been seeing some of the issues here. I haven’t completed my review yet though.

        I’ve poked at a few left-only solutions, but as noted those really aren’t super impacted here since the variation is already into the variable category.

  5. My Sigeyi Ax power dual side (Chinese power meter) on Shimano 105 previous generation (5800) do not seem to suffer from right crank low power reading. Perhaps older symmetrical design have no problem but only Chinese power meter make them now.

  6. Thanks for a great investigation. It is completely aligned with my own experience.
    I did a limited investigation myself after getting into real (fatigue) trouble at an early spring training camp in the mountains when I used a Stages LR (Ultegra R8000) for pacing. I had been using my Tacx Neo all fall and winter and it became obvious that it was a big difference in reported power (even more for me as my left leg is weaker due to an injury).

    I resolved my problem by getting a pair of Assioma Duos. My testing suggests that my Tacx Neo and Assioma Duo are within 2 watts at my FTP (270W). My Stages LR reads 18-20W lower at this effort. It looks a bit silly with power meter pedals mounted on a (unused) power meter crankset;-)

    Life would be perfect if Favero could sell a conversion kit to SPD-SL for the Assiomas.

  7. And I just ordered the Stages LR Factory Install at the beginning of June. Bugger…

    If there were more options for pedal based power meters, like SpeedPlay’s, and SPD-SL’s. I already have enough different pedal systems, and really don’t want to add yet another. Can’t some of these companies start being more agnostic, and release pedals with different cleats? It would be such a great thing for people with multiple bikes. COME ON INDUSTRY!!!

  8. GPLama: Three questions, and thank you for this analytical work!
    1. I have a Stages Gen 3 L/R Ultegra 8000 power meter. You don’t mention this solution, but I could disable my right power meter and just go with the left. Yes, it’s only a Left side power meter now, but improved accuracy would be the result, correct?
    2. I show about a 56/44 L/R power discrepancy when I ride. Is this due to the crank effect? FWIW, my Assiomas show about the same L/R discrepancy when I use them on other bikes.
    3. Why couldn’t software updates take care of this problem? I will dig deeper into the structural issues, but those are a static given set of conditions and thus, software should be able to offset the problem. Yes, they should eventually build on a better crank, but is the problem data volatility, or just always being off by a particular percentage? If the latter, companies could tweak the software.
    Thank you!

  9. PS: After watching Keith Wakeham’s video (thanks for link) I see the answer to my third question is no, software updates won’t adequately solve the problem–too many environmental and structural variables. But disabling the right power meter seems like a good interim solution, no?

  10. This is of interest to me:

    Stages Cycling:

    – They mention the loading of the spider and crank is different during the pedal stroke in ERG as opposed to SIM or riding outside – which could be contributing to the discrepancies.

    I recently experienced an oddity when racing in Zwift. I found that my FTP during the race jumped up by 29W. So 246 ERG in my workouts and FTP test, and 275 during the race, relatively flat and I did a lot of hiding. It was enough of a jump that Zwift Power nailed me with a WKG penalty. If this is the new reality how am I suppose to compete even if its just for fun? Is there any guidance you can provide?

    https://www.zwiftpower.com/viewtopic.php?f=11&t=5247
    https://www.zwiftpower.com/profile.php?z=783772

    • Hey Mick. I have 0% claim on testing accuracy but from all my experiences with a Garmin Vector 2 or Assioma, I’m 49% – 51% balanced.

      S-works 4iiii dual sided consistently shows me 46% – 54% or there about so I have my suspicions. It has been very predictable in the total number but the L/R has been weird for sure. I also get a reading on my right when i unclip from it and vice versa. Never a 0% reading even if I don’t pedal.

  11. I will gladly take the % difference versus using the tiny parachutes that the power meter pedals are. There’s a reason why all the top riders are using certain pedals. Assuming the data you use is from one meter and it’s consistent (from the same meter), who cares about total power output. It’s not like when you win a race, they ask you your power.

    Ride what you like and enjoy the ride.

  12. Great job by Keith and yourself for highlighting this issue. While it has been a while since I’ve done any FEA, I understand the principles that Keith went through in his video. While lots of effort could be spent by Shimano and 3rd party companies redesigning PMs for these cranksets, it seems to me that this effort would be better spent on simpler pedal based PM designs as a simpler platform for strain guages/PMs. i.e. get to closer to the “source of the force”, and thereby reduce relative system complexity. In the meantime, what Keith and yourself have done for PM consumers in highlighting the potential misrepresentation of PM accuracies by companies using Shimano crank-based PMs is very valuable. Thanks again for your time and persistance.

  13. Just out of curiosity – Have you tested these power meters using more or less the same protocol outside? Obviously without ERG… 🙂
    I hope I’m not mistaken, but from what I understand, all of the data you collected were done on the trainer. Could this be the reason ? (i.e., the somewhat stationery position of the bike).

    • The tests here were in ERG, yes. I have data from outside.. but not enough to collate and make any conclusions. That’s all this x2 in regard to workload. Which should be done at some stage. ERG (and indoor testing) is almost a perfect environment to test these power meters, and there are a LOT of other power meters that pass the indoor test without a problem. So it comes back to the power meter itself, not the testing protocol.

  14. Thank you and Keith very much for taking the time to test and test and test, your feedback to and connections with the manufacturers and writing (and video) it all up in such a clear way. Very much appreciated!

    Fortunately I haven’t noticed big differences in my power readings.
    https://analyze.dcrainmaker.com/#/public/7e5a2507-48ce-448a-5ccf-f501005ee180
    https://analyze.dcrainmaker.com/#/public/62ca6d30-2ab9-4bd4-547d-9bd0b2c3d9ec (minus som major error in the middle)
    https://analyze.dcrainmaker.com/#/public/94c18096-75f3-4357-4e02-f0d066610e78

    Listening to Keith, even 5-arm spiders are not really reliable for crank based L/R powermeters.
    So better move to pedal based powermeters?

  15. The greatest problem in this whole thing is the undeniable evidence that many power meter manufacturers have been playing with consumers. They unashamedly turned engineering and science into a marketing venture and truth was lost altogether. We manufacture the InfoCrank® to overcome all the issues in past and present power devices and have been saying these things for over four years, but other than those who need real numbers in order to win gold medals, very few wanted to listen and many people denigrated us for building what they said was an overpriced product. Thanks, GP Lama and Keith for starting this discussion. It needs to be said. The people who try to justify products that do not do as they say need to be silenced by those who demand that accuracy be proven. We totally agree that this is a large problem and it goes beyond Shimano cranks.

  16. Any engineer who understands measurement will tell you that accurate measurement relies on clean data from the sensor. There’s only one place on a bike where you can get reasonably clean data on torque and that is the crank arm. Anything else is marketing. There’s way too much noise from complex strain patterns in pedals, spiders, hubs etc. to hope to get an accurate result in real-world conditions, which is why so many power meters have incredibly complex algorithms to try to achieve a “believable” answer. However, it is not enough to stick a strain gauge on the crank arm, because the crank is twisted as well as bent by the forces on the pedal. The result is that the power meter has to be designed from scratch for accuracy with very careful placement inside the crank arm. To my knowledge only InfoCrank have done this, which is why their cranks are so popular at the highest levels where accuracy really counts.

  17. Shane, I’m wondering how this translates to outdoor riding? I’ve got a dual pioneer unit on a 9100 crankset and haven’t seen anything quite as drastic as a ten watt drop compared to my vector 3 (I use my indoor trainer for erg power numbers so I’ve never tested the crank indoors). From your recent podcast it sounded like outdoor rides were less affected than your erg testing. I don’t want to make any excuses for these companies, but even going up long climbs my L/R balance is typically within 1-2% in either direction. Is it safe to assume that there are issues with accurate power calculations, they are simply less drastic when riding outdoors due to the constant variation in cadence and torque?
    Thanks for the great work mate!

    • Outside appears to be less of an issue, however without a proper testing protocol I haven’t done any number crunching on this. I could spend a few weeks on it… but the outcome isn’t going to change what I’m seeing here indoors.

  18. Shane, All of the analysis was done in ANT+ mode I presume? Were any of the Pioneer tests performed in their proprietary pedaling mode? Reason I ask is after watching Keith’s video, I realize he’s talking about negative forces in combination with coupling. And since my Pioneer 9100 tracks perfectly with my tacx Neo, it made me wonder. Also since Pioneer is the only company that I know of that actually measures more data than anyone else.

    • I did a number of tests in Pedal Monitor mode with their CA600 head unit recording the data. Same issue. I’d be interested to see your results from same test protocol I’ve used here as you have a Neo to compare to.

  19. Another respondent mentioned pedal based PM’s. Until the industry has a viable solution, should the consumer go with the pedal PM’s and if so single or dual side?

      • Hi Shane: I love your content and details. Based upon this article and your review of the Assioma’s I’m thinking of getting a set. Given the Assioma’s have been out for a couple years now, any rumors of them releasing an updated version? Seems the life cycle of tech nowadays keeps getting shorter and shorter. Also, I’m a cycling enthusiast (~ 125 mi/wk) doing mostly group/solo riding. I don’t race. I feel as though dual sided is more than I need because I don’t race so wouldn’t likely need to know if my L/R sides are out of balance. Thoughts/recommendations?

      • I haven’t heard anything about updated Assiomas. They’re still releasing firmware updates (one is pending) that improve features of these units.

  20. @GPLama I’ll be interested on your take of the new Rotor INspider PM using the 110 x 4 Shimano bolt pattern. Will this have the same issues due to the asymmetric nature?

  21. This is excellent. I know it’s limited to shimano cranks but I get varied readings from my S-works Fact crank too (dual sided 4iiii). I wonder if it’s the same issue. At this point I just wanna stick to left only readings and not care about accuracy but just consistency :/

  22. Hi great work at all GPLama!

    I didn’t make so complete tests but as owner of a stage gen3 LR ultegra 8000 powermeter i came to the same conclusions as you.

    I compared this powermeter with some indoor trainer workouts on zwift (tacx Genius smart with dedicated Wheel equipped with indoor trainer tire inflated at 8 bar and trainer calibration done in a “hot state ” to avoid temperature effects).
    I did some power periods training around 200W and 320W NOT in ERG mode. I used a garmin edge 1000 to record the powermeter data on 1 second basis.
    Yes another point is that on my side, everything is updated to the last firmware…

    Roughtly between the trainer and the stage powermeter there is 10% to 12% (for 320W power intervals) difference.
    And i mean the stage powermeter Under evaluates the power!

    I looked at the balance and for my case, the left side gives the lowest value, not the right side.
    I also noticed that during an indoor session the balance is more 46% left 54% right as for outdoor rides it is usually 49% left 51% right.

    the Genius trainer is given for 5% error and in terms of feeling i am pretty confident on that. if I train considering the trainer power value, I feel I train right regarding my power zones.
    I feel the same difficulty and than i had during my annual medical checkup test I did with direct VO2 measurement.

    It is impossible to train with the powermeter on the basis of my medical checkup test.

    The question is, can we expect some improvements on this point from StageCycling in future firmware updates?
    I already had a ticket at the support for that with the *.fit files joined, but I got a fuzzy answer…
    Or should I directly look for another device, quarq dfour 91 or likewise?

    Best Regards

  23. I would be very interested to see the data from the exactly same test, but with different riders. I have the feeling manufacturers are looking at the data from various test riders then applying corrections to fit the data to the output measured by another more reliable device. So, when this is done, the result will better for anyone with the same torque output as the test riders. However, even in my case with my R9100 4iiii Dual, I originally thought what I was seeing was that as power increased, the L/R balance shifted more to the right. But when I compare trainer to non-trainer data I can see the on average the balance shift is more closely related to that, as in 53%/47% (L/R) for trainer, 47%/53% (L/R) for outside. Honestly, my take on this is what a huge waste of money spending $500 US to have 4iiii install the right senor to decrease accuracy.

  24. It appears my Stages LR Shimano meter has the same problem. I’ve shown a slight imbalance 52/48 with Vector 2 pedals, but my Stages has started showing in the neighborhood of 65/35. Question: For FTP testing, my options are (1) using both sides of the Stages LR, (2) shutting off the R and use only the Stages L, and (3) mounting up my old Garmin Vector 2 Shimano pedals. Which option would you think would give me the most accurate results?

  25. thanks for this big research job!
    i wasn’t expecting that, since everybody is telling me that the worst crankset-powermeter is better that the best pedal-based one.
    so i assume this isn’t true. given the same crankset (in my case ultegra), it would be more accurate an assioma or (my potential choice) the srm-look exakt, than the “giant system” i’ve been proposed. right?
    (my whole dilemma is bounded by budget issues, of course).

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