Agreed
I agree. I do think though, from what I understand to be the experiences of others, that 95% FTP should feel somewhat in the ball park of 95%. As opposed to 130%. Identical is one thing. At least, Iâd like to get to 5-8% +-
Sure, I have not stepped into the great details here yet to offer any advice. The magnitude you just mentioned is likely a mix of factors and not a single issue.
I was responding directly to the âidenticalâ comment and how I saw it as still incomplete. And I do think this inertia aspect could be making an impact on the order of 5% depending on the variables at play.
My take is that since you are comparing left only to total power, you may well be on a foolâs errand. Between PM accuracy, trainer accuracy, and L/R balance it is not hard for these to come to well over 10%.
I donât look at my L/R balance in general, but noticed my last long outdoor ride was 54/46, and I looked up another one and it was 53/47. Since left only double the left, the balance alone would account for 8% higher on one of those rides. Balance can change with effort level too.
I would recommend dual recording (ie record both pedal and kickr power), and do a comparison using a tool similar to the DCR tool. Also it would be good to do tests at different efforts, as this may shed some light on what the underlying issue is.
You wonât be able to get good evidence as to which measurement is âcorrectâ (or at least it will be very difficult), so I would set the goal of quantifying the discepency between the measurements so that you can use the scaling on the Assioma to get them to be âclose enoughâ in the power ranges that you care about the most.
Without other power meters to compare against, if you have a steady climb and an accurate weight for your bike+you+gear, doing a steady effort up a hill and using a tool to calculate power could be your best bet at another independent measurement of your effort.
Isnât this a moot point If we are keeping the power source constant and using powermatch? Ie if I apply x downward pressure on the left pedal, that reading should be the same whether indoors or outdoors. Then with powermatch that number should translate to relatively the same PE when calculating resistance on the trainer?
Yes, great suggestion, plan on doing this over the weekend.
I have done several climbs with friends who are almost of identical weight. Comparing data post ride if anything my power is slightly lower then theirs. Weâve also done quick power comparisons while climbing and theyâre within 5-10 watts. As opposed to 60+ watts Iâm getting on the trainer.
Yes, this I would expect powermatch to largely make this problem go away, unless you have a different L/R balance indoors vs out (not sure if this is a thing, but pedaling dynamics do vary a bit indoors/out, depending on gearing, etc.) I have a dedicated trainer bike without a PM, so I have never used it, and it doesnât really solve any problems for me.
I spent a lot of time chasing power mismatch gremlins, eventually finding that my kickr (gen 2 I think) would occasionally vary by +/- 20%. When it was really bad it was quite obvious without even comparing power meters. Itâs probably time for me to do another calibration check between my pedals (also assioma L/R) and my H3, but itâs likely close enough and ignorance is bliss 
Thanks so much for your help. Iâm OK with not using the pedals on the trainer. However, it would be really helpful to have an idea of what my true FTP is when out on the road (for races etc). Right now, the only way I can see around this is doing a 20 min test outdoors and using two difference FTPâs.
Interesting topic!
I have the same thing going on. I have my assiomas paired to my garmin watch when I ride and my trainer paired to TR and zwift.
Trainer is a KICKR V5. The trainer power is consistently higher than the pedals by about 10-15 watts at 290-300.
Outside, it seems that the power is easier to make, or at least it closely matches the trainer.
Not sure whats going on, maybe interference? I expected the pedals to read a little bit higher than the trainer due to parasitic loss but it is not so.
10-15 watts Iâd be happy to accept. At 300w Iâm getting a 60 watt delta.
gotcha, just saying maybe it is a similar issueâŚ
I would agree with the above note of trying this without running a workout in erg mode etc. Just set the trainer to slope/resistance mode and look at the power on your pedals.
My understanding of your problem is you could go ride a lap around the block on your bike holding 250w (as displayed on head unit, measured by Assioma), mount that EXACT same bike on the trainer without removing/changing/adjusting the pedals, and then attempt to hold 250w (still as displayed on head unit, measured by Assioma) on the trainer and be unable to do that for more than a few minutes?
I would stop even considering what power the Kickr is measuring here at all. If you have PM pedals then what your trainer measures should be totally irrelevant in all situations. I wouldnât get hung up on any âdifferenceâ you see between the the kickr and pedals because your pedals should be your constant in both situations.
If thatâs correct, I wouldnât think itâs a device/measurement/transmission issue, it would almost have to be something specific to you (fit, cooling, uncomfortable with trainer feel, etc) since you havenât changed any of the actual equipment.
Correct
What Iâm saying is my pedals- when used on the trainer are grossly inaccurate. I know my FTP is somewhere between 265-285w. I canât even get close to holding that same power on the trainer (using pedals as source) for any more than a couple of minutes. So if Iâm doing workouts on the trainer using the pedals I would have to set my FTP around 230 in order to complete a workout. But when I go outdoors my FTP would have to be set at ~275. This creates all sorts of issues including trying to do outdoor workouts with different FTPâs having to do outdoor FTP tests for accuracy between the two, and having two sets of power zones for training indoors vs racing.
Does that make any sense? Sorry if Iâm not articulating it well. 
Same bike, room is cooler than outdoors, feel very comfortable, actually more comfortable on trainer than outdoors. Again, I can accept 5-10% but 20%+? I canât see it being any of those things
OK, I really misunderstood the issue. Have you tried different gearing on the trainer? Low vs high speed can have a very different âfeelâ and some people find one much easier than the other - similar to climbing vs flat riding. I could see this explaining some difference in RPE at the same power, but I would be very surprised if this was your entire issue.
I donât have any great suggestions. I still think it is worth comparing trainer and pedal readings indoors - if they match thatâs a good sign the pedals are reading correctly, but if they donât match I donât think it tells you much by itself.
same bike, same power meter. Difference is between indoors and outside. There are essentially a few big differences:
- TrainerRoad app is controlling Kickr
- TrainerRoad app is using Erg and PowerMatch so that you have best chance of matching inside and outside power
Iâd start with taking TrainerRoad out of the equation. See if that fixes it. Then put TrainerRoad back in but turn off PowerMatch and Erg. Try that. Then turn on Erg but no PowerMatch.
Thanks. And yes, sorry, I couldnât figure out how exactly to word the issue clearly. Iâll do a 30 min workout on Sunday, record on both my Garmin using the pedals and TR using the Kickr. My suspicion is itâs going to prove the discrepancy, but as you said, then what? Iâve gotten a bunch of suggestions from others, Iâll play around with everything and report back. Thanks again for your patience, and thoughtful responses.
Make sure that TR is totally disconnected from the pedals.
Does TR have a crank length configuration for the pedals? It would be good to confirm that this is set correctly everywhere - Garmin, Assioma app config, and TR (if available).
As I understand it, the Assioma app setting will only be used if the connecting device doesnât set it when connecting.
TR does not (I checked and also researched). Garmin and FA are set correctly. Thanks again.
Sorry I havenât come back to you earlier, I ve been re-internally cabling the TT bike. With such a big discrepancy as you are seeing that (a 20mins test) is probably a good idea to start with. Hopefully you get to the bottom of why there is such a big difference.
This could be totally irrelevant for you but ERG makes a difference to me. Switch it off and do a 20mins test my power indoors and out is close enough but switch it on and use the ramp test protocol they can be further apart. When I last did ramp tests before ditching them for 20mins tests my results were erratic. Fortunately, AI FTP has done away with the need to do either but I do still have in the back of my mind on TTâs a power level thatâs normal for me based on previous TTs and keep the AIFTP for training. IMC AIFTP predicts about 30w higher than I know I can comfortably hold on the road though.
So you mentally readjust your FTP when riding outdoors for a figure thatâs 30w lower? Thanks for the response btw.
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I just did the test using DC Analyzer (link below). TR controlling/recording the Kickr, Assiomaâs recording through the Garmin Edge. The only difference to my usual workout is I wasnât using the Assiomaâs as a cadence sensor for TR. The reported cadence was 3 rpm higher on the Kickr (not sure if that matters) And the Assiomaâs reported ~10% less power. This was a much closer delta than I was anticipating. Pedals are one sided. So as far as Iâm aware a 10% discrepancy between the two sources is acceptable. Annoying but acceptable. Really appreciate you taking the time to help. I guess Iâll reduce my outdoor FTP by 10% or next month redo the ramp test using the pedals. DC Rainmaker Analyzer
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