Anybody running a dual sided Shimano 4iiii power meter?

I have a left side 4iiii 105 power meter and I’ve been happy with it. I wanted to upgrade one of my bikes with a dual sided 105 set up so I’ve been looking at 4iiii again. Does anyone have any experience with the dual sided 4iiii Shimano set ups? I know GP Lama has a video saying that accuracy with right side Shimano units is a known problem, but I thought the scaling feature with 4iiii might help with this. Any input is appreciated. Thank you!!!

I think the issue with the right side shimano power meters is more about power consistency than it is about inaccuracy. So it won’t always +2% or something like that that you can just enter an offset to correct.
However, @GPLama is in the forum so maybe you can get the answer straight from the lama’s mouth.

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Just to clarify as I get this “It’s only what he said, it’s no big deal” a lot.

There’s a lot more to it than what I’ve “said”. It’s the data I’ve collected, the consistency of this issue across ALL Shimano based L/R power meters (15+ sets and counting…), and the 30 minute engineering deep-dive video by a guy with his name on the patent for this power meter design. If there was an easy fix like scaling, this would have never been an issue.

Some of these units will get ballpark close enough for most people to be happy with. I can’t use them to test/validate other meters or smart trainers against… and that’s a massive issue for what I do.


Thanks for the input and all of the work you’ve done on this issue!! I spent some time looking at your website and youtube videos to get a better understanding of the issue. You’re nothing if not thorough!

I initially saw your review of the Dura Ace Stages L/R crankset where the right side issue was identified, and I hoped that maybe scaling with 4iiii would be a fix to get it “close enough”. I haven’t had luck in my limited experience with Stages, but now I see it’s a bigger issue related to the design of the cranks rather than Stages’ specific product.

Thanks again!!!

Running a bike with the new GRX groupo, 4iiii’s offers a L/R combo. Do you think the GRX crankset design will present the same issue that the 105/Ultegra/DA have had?

Just checked your video on this and definitely giving me pause for thought. I’ve discovered from looking at data on a previous dual-sided power meter that I get right-leg-heavy at higher power, and when I’m getting tired. So it means my current left-only Stages runs low, e.g. at the end of a ramp test where it matters most!

Would you be inclined to sell the Stages left-only crank and go for the Faveros? Or is upgrading to the L/R Stages likely to be a decent enough improvement?

Nope. That’s a different crankset. Likely to be all good. (Similar to the FSA crank I had with 4iiii L/R on it)


It’s hard to say. For my riding/testing/experience, the Assioma have always proven themselves to be the better choice.


Thanks. Time to crack open the secret page on the family budget spreadsheet!

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Just to clarify, @GPLama, you don’t think GRX will have the same issues as rest of Shimano? I’m debating between the L/R 4iiii crank and the Power2Max NGeco and would prefer to have distinct l/r measurement but Shimano’s history worries me

Given it’s a different shape than the Shimano road cranksets, maybe the GRX L/R won’t suffer from the same issues as the road chainsets. I’d need to see this tested using the same protocols to confirm.


I have had both a single side an dual side. I do not notice a difference, good thing about the dual side one is you can split it so you have 2 single sided meters, for 2 bikes, which is what i’m doing.

I have a dual sided Shimano R8000 4iiii power meter. I rode 55 minutes on CompuTrainer and the average watts the trainer calculated and what 4iiii power meter calculated were within 1 watt of each other. It doesn’t indicate that either one is accurate. However, it is good that I will have consistency indoors and outdoors. And for my own personal use, I am electing to believe that both are very accurate.

The left/right balance between CompuTrainer and 4iiii are very similar. On the CompuTrainer even if I pedal with one leg, I still get a reading that power is 35% on the side that has no leg pedaling. The 4iiii, notices pretty quickly that ALL the power is coming from one side.