Hi All,
I recently purchased a left sided only 4iiii power meter for riding outdoors. I compared the power meter to my Kickr, and the 4iiii is consistently lower than the kickr, by as much as 10%. This was even after waxing my chain and thoroughly cleaning the drivetrain (and calibrating both devices).
I know there can be discrepancies based on leg imbalances, but these seems really high especially with the power at the cranks supposed to be higher.
Has anyone else had these issues?
Thanks
I have a first generation Kickr and the power is way off compared to any of my power meters. This was a known issue with some of the first gen units. The newer Kickrās are much better in this regard. I also have a Tacx Neo and it is usually with a watt or two of my bikeās power meter (Quarq).
Left only or Left/Right dual 4iiii?
Left only for PM. Itās the newest model Kickr as well.
Ahhā¦ itās difficult to know whatās happening then. Youāre comparing left power (x2) with total power (Kickr). Both could be correct. The variable floating around is the unknown power on your right side.
As @GPLama has said already sounds like a left right imbalance issue to me.
Based on a quick mental calculation a 10% difference between power readings would mean roughly a 45:55 % LR balance which isnāt that extreme (someone correct me if Iām way off the mark!)
I can confirm that a 45:55 is possible and repeatable. I see something similar on a number of my rides using my PowerTap P1 pedals.
Obviously an imbalance is very individual, but it could very well be happening here. It is a huge unknown in this case, so it must be considered.
Thanks for the help!
If it is a leg imbalance then wouldnāt doing a quick experiment of single leg work with the left leg diagnose the issue (after dividing the PM wattage in half)?
Not likely. We donāt pedal the same with one leg vs two. None of this is āsimpleā math other than how the Stages does itās doubling. The realities of your pedal stroke canāt be captured without a true dual PM.
I had went around the same roundabout with left-only stages and a kickr.
n=1 but when I finally got to the bottom of it, issue was just the kickr reading way high. Same as here, maybe 10%.
Before I figured it out it drove me crazy for a while and eventually I stopped thinking about as my riding wasnāt held back in any way.
So Iām backing your PM to be right and your kickr to beā¦ optimistic 
I have a similar issue between my Stages (L/R) and my 2018 Kickr. The Stages seem to read about 10% lower at around 200 watts or above. Hard to believe that both manufacturers claim similar accuracy figures on the order of +/-2% (actually +/-1.5% for the Stages).
With 2 answers, there is no way to determine which one is correct (assuming that one is). I figured the Stages crank arm meters were probably more likely to be the correct one, but my local bike shop mechanic disagreed. Even considering that one may be more likely than the other to be correct, that may not be true for any pair of units. So, Iām back to the same quandary. (I know which Iād like to be correct!)
I doesnāt mater which one is the most accurate, just is itās consistant, pick one, use that all the time for your training ā¦ and worry about the training
Iāve done a load of single sided testing with my Stages L and simply divided by two to get an actual wattage. My results for my Kickr Core consistently read 10-15% low compared to two separate Stages units. With the Neo 2 the difference is consistently 2-3% low.
My FTP in ramp tests also shows a large difference when using the Core vs the Neo. The Stages deviates a little.
Now Iām not going to claim that I know how Stages works out their power figures, but Iām pretty sure you can simply divide a period of smooth single leg pedaling to get a basic idea of whatās going on.
I think itās ridiculous that power meters and trainers have claimed accuracy figures that often donāt add up. The average punter doesnāt have the time or the equipment to test several power sources to isolate a problem.
Yeah, you can pick one and get on with the training. That doesnāt mean you shouldnāt reject the faulty units and demand a refund.
Whatās the point of paying big bucks for accuracy if itās not accurate?
The OP should try and compare the Kicker to other dual sided power meters to see if it shows a discrepancy. We should really try to help each other out in this regard if possible.
(This isnāt directed at you specifically Chad. Itās a general comment and your quote was relevant).
After doing some more testing, Iām not so sure the power numbers are that different. If I just ride āuncontrolled,ā the power from the Stages power meter (read using a Wahoo Elemnt Bolt head unit) and the power from the Wahoo Kickr (read using the Wahoo app0 look reasonably close ā at least as far as I could tell from just looking at them while trying to ride as steady as I could. The Bolt read-out was for a 3-sce average power, while the Wahoo app read-out looked like it was instantaneous power. Note that this was just comparing the power levels by looking at the readouts for a few minutes at different steady power levels rather than through an extensive analysis such as suggested here: How to: Troubleshooting Power Meter and Trainer Accuracy Issues | DC Rainmaker
The big power difference occurs when I am using TrainerRoad to control the Kickr. So, I think it has something to do with how the Kickr tries to hold the target power or how ERG power is reported. Although I set TrainerRoad to use 3 sec power, the power level being is around 10% higher than the Stages 3 sec power at a pretty steady power level (although this was screwed up today by my somehow inadvertently turning on ERG power smoothing).
I didnāt check what happens if I use the Stages power meter power through TrainerRoad to control the Kickr and comparing that to the Kickr power output.
Interesting. I also just picked up a 4iiii left sided PM and compared to my KICKR core. They are almost identical in power and the ramp test gave exactly the same FTP.
I guess Iāll āhave toā upgrade to a dual sided power meter then 
Make sure to link to this thread for ājustificationā 
Iāve a similar problem with my Direto and Vector 3 single side. At cadences over 80rpm my Vector 3 read 25-35w higher than my Direto, yet if pedal lower than 80 the two are within a few watts of each other. Is it my left/right balance at higher cadences or the Vectors?
Kick core vs left only 4iii PM during a 30mn TT on zwift due to flats. Clearly a difference with my PM reading less but thatās what it is.
I wonder if people doing these comparisons have warmed up the trainer first. Iād put the bike on the trainer, ride for 15 minutes, then calibrate both power meters, and then do your comparison.
Other potential issue - signal dropouts. I found that my Stages could at times read very low because of signal dropouts. The culprit was bluetooth on my computer and especially my bluetooth headset.
At minimum, you have bluetooth going from a phone/tablet to the Kickr and the left only power meter talking to a head unit or something else. If you have interference, you can have spurious results.
