I find that my 4iii reads higher than my Neo at lower wattages and lower at higher wattages (that’s a mouthful!). There’s never more than a 10% difference though and some of this could be attributed to drive train loss.
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I am no expert by any means, but afaik a difference of roughly 5% between crank and hub is to be expected (normal drivetrain loss). I have not done enough testing to say how my higher discrepancy is made up, I’ll try to get that done in the next days.
I guess I will have to do my own GPLama lab test and hope there are no rabbit holes along the way 
Until then I don’t think the device is faulty - it could just as well be my L/R balance.
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Hi, I have checked in my stuff and I do not see anything that came through. Can you double check the email?
jerold@4iiii.com
Cheers,
Jerold
Hmmm… I just did some (limited) data comparisons, and I also see a pattern of high/low discrepancy as described by you. My efforts in this snippet only vary between approx. 100W and 250-300W, but the variance already seems quite obvious.
I would be interested to hear opinions if this variance between 4iiii (left-only) and Tacx Neo is to be expected / normal. Feeling a bit insecure about my purchase now, I guess I will have to do more testing with wider power range etc.
Edit:
Obviously, the 4iiii is always reading higher than the Tacx in this snippet - but this could be due to L/R imbalance as well as drivetrain loss, and can easily be corrected via the configuration app. The problem is, that the result of this configuration would be something like the purple line, which would be too high/low, depending on power output. My original post was not very clear in this regard.
!
Explanation:
- values are 5s smoothed to improve readability
- orange line is 4iiii original (via Wahoo Bolt)
- blue line is Tacx Neo (via TR)
- purple line is 87% of 4iiii original (to match Tacx average)
Tried again using a different email address in case it’s going to your spam. Thanks!
Size of attachment may also be the issue
Hi,
We just got it and have replied. Have a great day.
Cheers,
Jerold
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Well. Did a comparison on Thursday with my new power meter, got many spikes. Here’s what it looks like. The TR workout was Ebbetts. No power smoothing was done on the power meter (Stages L 105 5800)
It looks to me like my left leg contributes more power, and therefore overall power from my power meter reads a bit higher than my Kickr. I don’t have a Wahoo or Garmin cycling GPS, so I had to use one iPhone for my TrainerRoad my other iPhone for recording the Stages power.
@Agglo I feel similar.
I’m using several pm’s and on my bike i have left pedal power meter. Indoors im using dual sided and i have no use for the ekstra information.
I migt have 2% difference sometimes other times no difference.
Outside i just gauge my effort and one sided is a little more spikey data wise but still good and effective for pacing
My 2c on the OP question: I have a stages left-only power meter, and for gauging efforts outdoors, one side is enough. I’m rubbish at pacing from RPE, so just looking down, seeing a number, and knowing “yeah, I can hold this effort to the top of the hill, no problem” is great. If I was going to do a lot of serious outdoor training, I’d have more interest in a dual sided PM.
Relative to my kickr core, the stages is way off (under by 10-15%), especially at higher wattages and when I’m tired. It’s mostly due to my natural l-r imbalance. If I try really hard to pedal even, smooth circles, the two power meters line right up.
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One downside of a one sided meter that I’ve found is when using it with PowerMatch in ERG mode. While pedaling, if I slightly change the effort on each leg so that I relax my left or right slightly, it has a huge effect on the measured power and can make the trainer bounce around trying to follow the power input. It’s not a huge deal but I have found it to be slightly annoying and if I upgrade bikes I will likely go for a L/R setup or a spider-based version that is measuring both L/R.
I agree that a one sided PM is not great for powermatch. I use the PM in the trainer for indoor workouts.
Power meter was definitely worth it. Like you I had a trainer but no outdoor power meter. I purchased a stages power meter. Well worth it. Not sure if left right would make any difference for me. I dont race either.
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You’re comparing two things that aren’t measuring the same thing though (as mentioned)
I think until someone compares left to left I.e. pedals like @gpl then it’s not a fair to write off the 4iiii single. (I wonder if the 4iiii unit that Shane has now will work left only to test this)
… also I don’t exactly follow power meter sales but I imagine a very large share of the market will be single sided crank based so this kind of review video may even do well.
Finally if you checkout DC Rainmaker review from a couple of years back - I believe there he also said the 4iiii reads low at high watts, so maybe the lower wonkyness can be explained by L/R imbalance but the upper is expected. Anyway need a proper left to left comparison. Or I guess you could just redo your test with only the left foot on the pedals!
If I recall correctly, that might have been gen 1 version of 4iiii and because of DC’s non-symmetrical pedal stroke the 4iiii was reading funny. Based on the problem and his feedback, they developed the 3D strain measurement system which eliminated that problem.
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I did more comparisons, and it looks like the Stages reads 10-15% higher than the Kickr. I now have an Edge 520 which I used to record the Stages, but I couldn’t record 3 sec smoothing, though it display 3 sec smoothed power.
Edit: Did further analysis and found a constant offset between my Kickr and my Stages L
Hi
Did the 4iiii power meter fit or did you go with another option?
I am in the similar situation 2018 Domane SL 6 and the battery test goes 3/4 of the way.
Thanks
4iiii said they could custom fit one to an existing crank but instead I went for a Power2Max with Rotor cranks. Very happy with it so far.
Thanks for the quick reply.
The Stages crank seems like it has the meter a bit further down the crank than 4iiii - where there is more room on the Domane. But hard to tell from pictures on the web.
I was hoping someone had already done it. But my local bike shop great and they are willing to order one in and see if it fits.
Thanks Again.
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For others that might be looking, I did order a 4iiii left side crank power meter 175mm for a 2018 Domane SL 6 with a large frame - it fitted no problem with a couple of millimeters clearance.
Glen
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