Dual-side 4iiii - Shimano R8100 Ultegra crankset

Hi all,

I just received my new SL7 equipped with the new 12 speed Ultegra Di2 groupset and I looking at adding a crank-based power meter. I have owner a left-side only 4iii power meter on a 105 crankset already and had a good experience with it. I do have a significant left-right leg imbalance and would perhaps like a more accurate power meter (without having to use a ratio setting on the left-side). I’ve heard some pretty negative things on the dual-sided Shimano based power meter and I’m wondering if that would also apply to a 4iii factory-installed power meter.

I would really like some input on this before I invest the 200$ difference between left side only and dual-side.

Thanks all!

According to DC Rainmaker, your worst power meter option is a shimano crank based system. You would be better served with a dual sided pedal system is my guess.

I have a pretty big left/right imbalance due to a major knee injury, I use a left side only which at least nets me something to train with, I don’t see myself getting that imbalance properly fixed so I just roll with it. I would like to try dual sided pedals to see where that deviation in power balance happens in my power curve.


Shimano appear to be the worst of the bunch according to DCR and @GPLama. 4iiii haven’t figured it out with their dual sided shimano models yet either (though their issues are the same as they were with the previous generation and not as bad as Shimano’s own brand). Stages do appear to have found a solution though - their strain gauges on 8100 and 9200 are on the front and back of the RH crank arm rather than the inside of it. Both of the gurus approve of that one, which seems like a good development.

I’m currently debating whether to unseal the box and setup my Assioma Duos as part of a near-identical upgrade situation to yours, or to return them and go for the Stages Dual option instead.

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I don’t like the current pedal based solution as its either a out of the box solution with the garmin vector that doesnt seem to be reliable or the look-based assioma. I dont really like look pedal/cleats and the shimano solution from Assioma is not great right now.

I suppose my best bet is the cheaper left-sided for now.

Why do you say this? Are you concerned with the Q-factor?

I’ve been using the Assioma Duo-Shi and they’ve been great. The increased q-factor may bother some, but for many it’s not an issue at all.

I swapped my dual sided factory Shimano 4iiii crankset for the new Shimano dual sided with the rechargeable battery. I did this to go from 172 to 170 arms. I used the 4iiii set for about 6 months. I have had no issues with power readings from either set.