4iiii Power meter (left only) vs Kickr Core

So I just bought a brand new 4iiii left only PM so I can continue my training outside.

I installed the PM and went for a ride. I was so excited to be outside finally that I crushed the ride. When I got back to look at the power data I noticed it seemed drastically lower than what I’ve been seeing inside in relation to my heart rate and RPE.

So the next day I decide to throw the bike back on the trainer (brand new Kickr Core) and simultaneously record the data for comparison. I set everything up, did the calibration, spin down, power smoothing off, 1sec recording on Garmin, etc, etc.

Sure enough after the 30 min ride the data from the 4iiii was significantly lower. It was showing approximately 20% lower than the Kickr Core. A little time on Google tells me that, assuming both meters are operating correctly, the Kickr would normally read a little lower due to drive train loss, and in general the power meters could be 4-5% out from each other anyways.

I have a email into 4iiii to see what they say. 20% low (ish) seems quite a bit off. Obviously its entirely possible that my Kickr is out too, in a perfect world I would have a third PM or another trainer to compare it against, but I don’t.

Anyways, I guess we’ll see what they say. Anyone else have similar experiences where the trainer was lower than the crank/pedals?

Did you do a spin down calibration on the trainer? I’ve found my 4iiii left side PM to be about 3% higher than my Kickr after a calibration and zero offset on the PM.

Your right leg is most likely stronger than your left. That’s what happens with me and it’s something that drifts depending on my fatigue and power output.
Remember that a Left only will simply double the imbalance.

In saying that I do have a Kickr Core that reads lower than both my Neo2 and 2x left only Stages (single leg drills to confirm). If I try to do a workout on the Core at the same setting I get crushed.

+/- 2% Accuracy my arse!


Before testing, warm up everything for 10 minutes and then calibrate both trainer and power meter, and then do your test.

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Unless you’re putting your arse through a proper testing protocol with solid analysis, I wouldn’t be making those accuracy claims.



I thought I did pretty well at testing. Not quite as anal as some but pretty thorough.
It sometimes seems like you’re the tester for all the new releases these days. Stuffed if I know why a company would send you a unit that then fails in the Lama Lab.
I can’t wait to see the outcome with the new SRM MTB pedals.

I used two different power meters and tested the Core and Neo back to back. My Kickr Core consistently reports 10-15% lower than the crank based PMs and the Neo 3-7% lower( not taking drive train losses into account).
There’s definitely an odd one out in my case.

Out of interest Shane, do you know what the sampling rate is on the Stages G3 cranks?

I won’t be getting the SRM pedals any time soon. No need to worry about it failing the Lama Lab Test.

With enough data showing any power difference outside spec, companies should replace products. Lionel Sanders is now on the case regarding power accuracy / standards / etc. We’ve been saying it for years. Nothing changed. If it takes a pro to say it to get some kind of industry certification setup, great… but every power meter company is an island…

Stages. They have 64Hz in high speed mode. I haven’t toyed with that.

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Thanks for that. 64Hz is pretty quick.
I was pondering how much of an impact sudden spikes had on the readout.

You know https://analyze.dcrainmaker.com/ just got a whole lot funnier after your post above. :grinning:

Hopefully Ray will do a test on the SRM’s then. Until then I can dream about owning an accurate LR pedal based PM that can be swapped between all my bikes.

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Yeah I warmed up the trainer for 10 mins and did a spin down.

You have a good point about the possible leg imbalance. I’ve done leg work in the gym for years and never noticed anything but who’s to say exactly. If there was an imbalance wouldn’t it have to be very significant to throw it out 20%?

Yeah that’s exactly what I did. I followed @dcrainmaker guide to troubleshooting issues.

Ran multiple tests, same result.

20% would be pretty significant but not outside the realms of possibility. That 20% would actually be a 10% imbalance and doesn’t take into account any drive train losses.
A clean drive train in good condition can be a couple of percent. A dirty or worn drive train can blow that number out.
Run a single leg drill at a fixed wattage and then divide the PM reading by 2 to get an idea of the real difference. Hold a steady wattage for a couple of minutes and it’s easy enough to see what’s going on.

I have two Stages that I believe are within 1-2% of each other and a Power2Max Ngeco that is within 3% of the Stages on the low side. My kickr core will match my stages for 20-30 min after a spindown / calibration (and clean drivetrain) and then drifts to 10-15% low. I have 0 trust in my kickr core power reading and always use power match or run it in sim mode.

I got the Ngeco to assess L/R imbalances and I slightly favor the right leg (52%) but no major differences. Based on that I would expect the Stages to read slightly low.

Yeah, 20% is a big divergence…maybe if you had a really inefficient drive train and a pronounce L/R imbalance? Seems a stretch, though…I don’t have any answers but I do have a question…

What crankset? Not that it makes a difference. Just curious.

Also, getting ready to walk out and test a 1.4GHz system & trying to adjust my frame of reference to 64Hz being fast. :smiley: Tech is awesome.

It’s a 1 year old Ultegra R8000. I literally just stripped the bike down and did a full clean. The drive train is sparkling! Chain has some K’s on it, but the chain checker still showed it being really good. I would say its still 75% life left at least.

Interesting. Thanks for your reply.

I didn’t notice any drift over a 30 minute ride. I may try a 1hr+ and see if it does anything goofy.

I really need to find some reliable pedals to test my L/R balance now…

Kickr 2017 direct drive and similar experience (I’ve seen it drift both high and low!). Always run PowerMatch on TrainerRoad, works well and makes the experience more like riding outside.

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Today I did exactly the same test on a Kickr Core vs a 4iiii (Shimano 105) left power meter. My experience is that the 4iiii reads 12 to 18 % lower than the Kickr Core. The difference gets smaller when the power output gets higher. At 120 watts on the Kickr the 4iiii reads 98 watts (-18%). When doing 250 watts on the Kickr, the 4iiii reads 220 watts (-12%).

I did the test according to GP Lama’s youtube instructions. Everything was updated, very clean and after a 10 minute warmup I did a spindown on the Kickr and a zero-offset on the 4iiii. My guess is that my left leg is less strong then my right leg. Next powermeter will be a dual sided one.

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Check your scale factor in 4iiii app. Mine changes by itself, which is super annoying.

If you’ve got different length cranks on different bikes you’ve got to change the length on your head unit as that takes preference over what had been set in the 4iiii app