Humbled by New Power Meter - What Now?

I’ve been training for the past 5 years or so using a 4iiii left crank arm exclusively, switching it between road and cx bike when required. I recently decided to pick up a new power meter for my MTB (Power2Max) for simplicity and since the 4iiii crank arm won’t fit that bike.

Decided first to do some comparison between the 2 PMs just to see how they compared. Since I can’t fit them both to the same bike, I ran 2 quick tests back to back, using the start of ‘Davis’ as the benchmarking test. I ran TrainerRoad on a laptop, letting it control my Wahoo Kickr Core, with the PM set to record cadence only. I recorded the PM power on my Garmin head unit. This way I recorded the Wahoo power and the PM power for each run. I also did this directly after that day’s workout so the trainer was warmed up.

The results are not quite as I had hoped, although not completely unsurprising. I’m pretty impressed how closely the Kickr tracks to the P2M, however the 4iiii seems to read noticeably higher. Although seems to be roughly a 25-30W difference rather than a set percentage. I guess this could either arise from an accuracy issue or L-R balance since the 4iiii reads left leg only (though i think it would have to be something like a 60/40 split for those numbers to make sense). I’ve posted the graphs (1s and 10s averaged) and summary below. Also noted the crazy amount of smoothing from the Wahoo!

It kind of is what it is. I’d probably trust the Power2Max / Kickr since they’re measuring overall power output. However what I’m questioning now is how to proceed. I do all of my indoor training on the Kickr with 4iiii powermatched. However I plan to do some workouts outside on the MTB, and so the intervals would be too tough and if I drop the % then my TSS won’t be calculated accurately. I could drop my TR FTP and use the Kickr power indoors (essentially obsoleting my 4iiii), but it seems like if I have a road PM I should use it.

Anyone else been in a similar situation and have a solution that works for them?

Results Summary

I believe you are not balanced .
If you push maybe 5 % more on the left leg, those differences would be complaoned. This would be my case , because i am pushing 55 to 45 % according to my assioma favero duo.

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Yeah that’s the one piece of the puzzle I don’t have hard data for. If that is the case then, if power reading is accurate; it’s something like a 60/40 split at the lower wattages and 55/45 at the higher wattages.

I’ve noticed this with a friend I have who got one of these PM. He previously didn’t have one, then bought one and started to post the data on Strava. His power was impossibly high for his speeds, etc. He’s a fit rider, but not like that. I’d just get rid of it and buy a stages if you care about it being accurate.

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To be honest if i was going to ditch the 4iiii I’d probably go for another P2M now. I think the Stages is more or less equal to 4iiii (unless you mean the L/R version, in which case I’d just add the R option to my 4iiii).


Do some left leg only pedaling on the trainer with 4iii and Kickr dual recording and see how the numbers compare? I think (never owned a single leg PM) the 4iii will still double your left leg power, so you’d need to double the Kickr power to compare. If the 4iii power tracks well with 2x Kickr power that would suggest the PMs are similarly accurate and the discrepancy you’re seeing is down to your L:R balance. If on the other hand the 4iii is 25-30W below 2x Kickr then the issue is likely due to the PMs not your L:R balance.

Of course also possible the numbers are somewhere in the middle meaning you have a L:R discrepancy AND the PMs read differently!


I lost 30w “FTP” over night when going from 4iiii left only to a Quarq spindle PM…

Was stronger on left leg so…


I had this problem for 5 months. My imbalance is 4-5%, but it gets 2x by the calculation. The solution:

  1. Get the L/R power-meter
  2. Adjust all your historical data to reflect the real power you produce.
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Good idea, I’ll give this a shot just out of interest.

I’ve read mention of being able to apply an offset to 4iiii PM so if i can figure out how to do it, i might apply an offset of -30W to the 4iiii and also adjust my FTP by the same amount. It won’t be exact but i think it might get me closer.

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No power meter measures the same. So if one says 275 and one says 256 once there constantly saying the same numbers than your all good

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There is your answer…use the Kickr inside and the P2M outside.

Don’t overthink it…our bodies are not that specific. If the numbers align well from your test, they are good enough to use separately but reliably.


You can do the offset easily in the 4iiii app.


I think this might end up as my solution. Everyone always says powermatch is better. But maybe not in this case. I still need an outside solution for the road bike so i will try to offset the 4iiii down for that reason.


I am not sure that will work.

Both my KickR’s do not track my single or dual sided power meters at all. 15-20% difference, some of which is the drive chain loss.

Two things are certain in life: death and taxes.

  • L-R (in)balance is not a constant
  • cycling has a pm accuracy problem

True, at 110% plus FTP I have no imbalance at all.

FTP and lower its about 5%

Also, to many people think that power meters are precision instruments when in they are not.

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That’s surprising: my Kickr matches my Assioma Duo pedals within about 1%. Several friends with the same experience (we’re all on Kickr V4 or V5). Have you tried to do a factory spindown?

Power meters are miles from perfect.

Particularly, from brand to brand. It’s a basically a ^%$& show.

If you’re Kickr matches your pedals, then technically, one of them is lying. Drivetrain loss is a thing…


I had a similar “issue”: for about three years I used a 4iiii one-sided power meter, and when I got a Quarq DZero on my new bike, I noticed I had a 45:55 leg imbalance. I don’t blame the 4iiii, I blame my smart-lazy body: it figured out that to increase the power number on screen by 2 W, it only had to produce 1 more watt in my left leg. Smart. But lazy :wink:

I have gotten rid of most of my leg imbalance by simply putting the 20-second average of my left-right balance on my Wahoo’s screen during workouts and trying to focus mentally on the weak leg. Over time that took care of it. My right leg still doesn’t have exactly the same endurance as my left leg, but it is getting there. Now there are even periods when my right leg (which was formerly my weaker leg) is putting in more work than my left leg.

I wouldn’t worry about a one-sided power meter on outdoor rides, though: it should be good enough for pacing and recording your TSS properly. Plus, once you train to ride in a more balanced way (I think +/- 2% is fine), you will continue to do so when riding outdoors.


I’ve had a few power meters and not really found much consistency between them, Kicker V1 (not renowned for accuracy) was about 50 watts higher than my Stages V1, then got some Vectors V2 and they were about 30 watts higher then my Stages, Then got a Neo and lost about 10 Watts. Just trained with that for a few years and was happy, but last year got some assioma favero duo’s and got that 10 Watts back, I then got a second set of assioma favero duo’s (don’t ask) and I think they are a few watts down on the other pair

I feel that if you chase having your power meters line up (even from the same brand) you are going to lose a lot of sleep, my feeling for me, is that it just helps with pacing and getting me in the right zone if I am doing intervals outside (I always use the Neo indoors) It does mess up the AI FTP detection a little bit, but it is what it is

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