Left only Stages Power Meter

Been using Stages (Left only) power meter for 3+ years.

I’ve had absolutely no issues with it technically, but i’m curious about full power accuracy variations.

I realize it multiplies my left leg power X 2 but if i know my left leg is much weaker than my right leg, how off (in %) could be the power readings? I’m just curious if it could be significant in any of the metric power durations of 5 sec, 1 min, 5 min, 20 min , ect ?

Obviously, it does not change much because i enjoy the consistency, but just curious about possibly power % ± from 2 leg measurenent systems.

Thanks.

some quick & simple math - assume you are 60% left and 40% right. During a 100 watt interval that is 60W left and 40W right. So doubling left the PM will output 120W instead of 100W for a 20% error during that 100W interval. Not saying that is exactly right, but should give you an idea for accuracy variation.

I just upgraded from left-only to Stages LR and saw 51/49 power split on first ride, and 48/52 on second ride. So that means my left-only was pretty accurate on estimating total power.

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Not trying to be controversial, but does it really matter? What would/could you do differently if you knew?

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The Stages is consistent to itself, but not accurate. It’s better than virtual power, but having owned a Stages, I would not buy another one.

Go get a Power2Max NGEco for the same price and you wont have to worry about fit, power spikes, or the power being 25w off compared to a different power meter.

(for reference, I have a 50.5/49.5 split between legs according to my Quarq data)

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my question was one of curiosity for the % of power variance and not one of application. no offense or controversy taken!

Esentials… New power meter - new FTP test. If you remember this, there will not be no deference.

Here a real world comparision, a race in two subsequent years. Curiously, it took me exactly the same time in both years. Values are average wattages per climb. Times between the years differ only marginally. Everything “ceteris paribus” (e.g. same bike, same weight, same weather).

Simulating the climbs with the respective models gives fairly good estimates for the P2M curve whereas the Stages is just off.

This was the first time I started thinking about my left-right balance. Got a pair of P1s afterwards and started looking into my pedalling in detail.

My legs fatigue differently, left leg (the Stages leg) is more fatigue resistant. That’s why it overestimates later in a ride.

I did ramp tests after 1000, 2000 and 3000 KJ of work. I introduced imbalance largely into Tempo/SST zones. My main racing zones.

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This is kinda interesting but… the data is suggesting your left leg fatigue resistance accounted for a 50w variance in power at the 1 hr mark? Seems a little excessive, but I guess if you were cranking 25w higher with that left leg in 2015 vs 2016 that could make up the difference.

I started with a Stages L (v2) and always wondered about potential imbalance so I upgraded to a Stages L/R and typically see a 48/52% split. Nothing to write home about. If I could re-do it, I would probably go with the Favero Assseoma Duo so I could switch to future bikes more easily. Anything crank-based seems like a waste given the limitations of swapping.

To answer the OP’s question: if you have the budget and the interest, I would say it’s worth upgrading to total power. Doesn’t have to be true L vs. R but having total will always be more accurate and if you plan to spend a lot of hours in the coming years training to power (and on TR), it’s definitely a worthy investment.

My training partner uses a left-only stages and it records at -5.5% when used on my Tacx Neo and his Kickr. The discrepancy can easily be explained by L/R power imbalance and/or the stated error of the various devices. The important thing is that his stages is consistent in this reading so it doesn’t matter except for his ego.

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This is correct, assuming you aren’t putting any other power meters into the mix. I had a Quarq on my road bike and Stages on my mountain bike and assumed they were much closer than they actually were, which as a result meant that my pacing on my MTB was much slower than anticipated.

Doing 275w on the Stages was really equivalent to 250w on the Quarq, which completely invalidated nearly a season’s worth of PR data for me.

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Which is why I base 99% of my outdoor riding on RPE and simply use the power number to validate that feeling. I don’t see a lot of value in comparing PRs between disciplines. Too many factors to consider IMHO.

I consider the 1h data point more as an outlier. This was the climb where 2015 and 2016 times differed a bit. Not too much though. If you apply a model on the climb and correct for the time you pretty much end up with a data point within the trend.

By the way, I worked actively on this for two winters. Could bring down my imbalance quite a lot. Yes, I know, they always say you shouldn’t, but it’s just fascinating how you can control your pedalling by just having the L/R in front of you. Always paid attention to it while doing tempo and SST intervals in the basement. Just paid attention to it, this was sufficient.

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Agreed, it’s just that most products are not set up to deal with multiple power meters where the offset is more than within a 1%-2% margin of error. My TSS/CTL and Power PR graphs were materially affected by the Stages being off by that much compared to the Quarq, hence why I ditched it.

(this is only a problem if you have multiple power meters on multiple bikes)

I feel your pain, consistent data is the ideal.

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Same question here. I have a Stages and recently bought a Cycleops Hammer. The Hammer is reading about 10% higher.

Even if the Stages is ±2% and the Hammer ±3%, there’s still a difference. I think my left leg is a bit weaker than my right as I’m right handed. So this would totally make sense. Can I change that probably not.

Conclusion: Stages is great as long as all your power meters are left sided.

For what its worth, this is from recent DCRainmaker power meter guide:

Would I buy it: I have zero issues with the Stages LR in terms of purchasing one, and in fact did so this past June for my main test bike.

I’ve only ridden twice since upgrading to Stages LR. FWIW I’ve actually had more issues with Kickr17 optical power meter than with Stages Left only in 2 years.

My left stages reads higher than my left 4iii. In the 4iii app you can adjust the settings to add a little more so they match since doing that they have tracked perfectly for 10 months.
However as has been said I am stronger in my left leg so I know my FTP of 282 is actually about 275. I don’t really care but when I got the 4iii after having the stages I wanted it to be left only so I didn’t have to change any ftp settings and knew I could scale the power so it all matched nicely.

I got a Stages L 105 for about a month now, and I’ve found that it reads 12-15 watts higher than my Kickr. I haven’t calibrated both the Stages and the Kickr before each ride, so there’s that.

Mean power for Darwin from DCR Analyzer:

Mean Power from Mary Austin -1 from DCR Analyzer:

My Stages LH meter reads quite a bit higher than my Stac Halcyon which in itself is no problem as you can adust the reported power on the Stac to match the Stages. Except I have a L/R imbalance which reduces as a) I fatigue and b) the power I’m producing increases. I suppose I should get 3 offset values for Endurance, Sweet Spot and VO2 max intervals but perhaps I’m overthinking things

I found something similar myself, also using a Stages 105 left-only PM (gen 2), compared to my 2019 Kickr.

The comparison I did was done by setting a target power in ERG mode in TrainerRoad (i.e. controlling the Kickr, with the Stages not linked to the TR app), let things stabilise for 30 seconds, then record a minutes worth of data to get an average power from the Stages (via my Garmin). Both devices were warmed up and calibrated beforehand.

I tried different gears and different target powers. I found the Stages read 5-13W higher than the power that the Kickr was targeting, as shown below:

High gear: 270W target, stages 282W
Low gear: 270W target, stages 283W
High gear: 129W target, stages 134W
Low gear: 129W target, stages 139W

Not perfect or ideal, but it was good enough for me, especially as I do my TR workouts using powermatch, to use the values coming from my Stages.

Concerning the original question, I use Stages PMs on my other bikes, and so while there’s a good chance the power value is inaccurate due to L/R leg imbalances, those errors and the reported power values should be consistent at least, which is the important thing.