4iiii to 4iiii comparisons power meter


I’ve just pulled the trigger on a 105 version of the left sided 4iiii for my winter bike, which will be a large part of my training (which is how I justified it!).

I have the Ultegra version on my good bike, which I compared to my Hammer at the start (it matched, consistently). At the moment, I ramp test/ weekend workout on the Hammer, and then weekday do sessions on portable hybrid rollers at work. I’m trying to save the wear and tear in the good bike by using the winter bike, as well as having the option for outdoor rides.

Anyone had any issued in 4iiii to 4iiii comparisons? I’m assuming they’ll be like for like but maybe that’s optimistic…

I don’t have any data or evidence to back this up, but I had heard that because the construction of the ultegra and 105 cranks are slightly different that they may have slightly different strain readings. It has to do with the thickness of the metal in the area where the PM is cemented to.

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I think they only claim +/- 2% or something right? So in theory one could be 2% up and one 2% down, and you end up with 4% difference. I’d compare them both to the Hammer, then in the 4iiii app you can add a scale factor. Use that to bump the reading of one up or down a little to make them match if they don’t already.


I run multiple and don’t have issues, make sure you are properly calibrating both.
Stages to 4iiii i would see issues however.


Sorry to jump in on this thread…my mate is looking to buy a 4iiii left sided crank power meter. Does anyone know what bottom brackets the 4iiiis are compatible with? The vendor he is looking online at does not seem to make any mention of which bottom brackets the devices are compatible with.

That’s kind of an odd question. The 4iiii cranks are compatible with any crank listed in each model category. The BB for each is determined by the crank spindle diameter. So Shimano at 24mm, most SRAM at 30mm, and their lovely DUB (28.999999999) is all you need to know.

Simply match the 4iiii crank arm to the existing or desired crank and BB from the current bike.

Rondal, what have you found comparing Stages to 4iiii? I’ve found my left side Stages (carbon SRAM) reads about 9% higher than my left side 4iiii and my Kickr. (The 4iiii matches my Kickr quite closely). I’ve set the offset on the 4iiii +10%. This way the 4iiii (which is on my outside gravel/cross bike) is at least in the same ballpark as my Stages/KICKR set up, which is on an old bike on the trainer.

Anyway, curious what you’ve seen.

So, what has confused me is that when i first got into power meters I used Stages (now on garmin vectors). I remember that when purchasing the Stages (or at least i think i can remember!), you had to select two things: crank length and bottom bracket type. it’s actually for a mate who is new to training with power, and i’m not sure what current crank he has. I guess what you are saying is - simply establish current crank spindle diameter and ensure the 4iiii crank is of the same type?

  • That is true for a couple options. Sram for instance, offers some road cranks in GXP, 30mm and others? not spending the time to look).
  • As I said, you have to match whatever you already have or plan to buy. All dependent on that and the best thing to do is simple open the power meter site and see what they offer.

Stages read high.


Agree. my stages reads 20 watts higher i reckon than my garmin vectors. first time i test with them i thought i was bossing the test, though!

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This was my experience with GRX left side power meters too.