Power from 4iii outside and Kickr Core inside

Hello,

I’ve just bought my first power meter. I went with the 4iii. I can’t justify the cost of a dual leg meter. I want to use it for pacing my outdoor rides and interval training etc. I have a number of options of calibrating (or not) the power between the Kickr Core I use with TrainerRoad and the 4iii and wondered which you guys thought would be best.

  1. Trust that the Core and 4iii power readings will be roughly the same and use my Core/trainerroad FTP for outdoor rides. I think I probably have a difference between left and right legs, because I can feel my right spins in smooth circles whereas my left does not. So option 1 is probably a bad idea.

  2. Do an outside FTP test on the 4iii and use that result for outdoor rides. Then, If my FTP has improved after doing a TR ramp test, I can adjust the outdoor result by the same number of watts.

  3. Put 4iii on my Kickr Core bike and look at the difference in power readings and use 4iii’s scale factor to match them as best as I can. If I do this option, should I measure the difference between max power, average power or ftp?

Many thanks
James

  • Put the 4iiii on whatever bike you ride on the trainer.
  • Do an indoor FTP test (e.g., Ramp Test) using the 4iiii as the source of power.
  • Use that FTP for all TR workouts.
  • Enable PowerMatch which allows TR to control the Kickr resistance based on your 4iiii power output.

Since you will be riding the 4iiii outdoors, it makes sense that you would want your indoor and outdoor numbers to be consistent and meaningful. Thus, use the 4iiii both indoors and outdoors.

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What @KickrLn recommended is probably the best option, but if you do not want to swap the meter between bikes, or swap bikes on the trainer then I would try some variant of #3 -

If you run the 4iiii on your trainer as a test you could disable powermatch and then do a workout in ERG mode with mid-to-longer intervals. Then looking at the power difference over a consistent interval may tell you how close the meters tend to line up. You would probably want to compare low efforts, high efforts, early and late in the workout to ensure fatigue or device temperature doesn’t start to play into it. I would probably “generally” compare average power for a consistent interval in this case, but also visually look for weird differences in initial settling in.

In my personal case I added Assioma DUOs to my KICKR and noted the numbers were close enough that I felt good about past training with only the KICKR (~5-10W different across a variety of scenarios). Now I just run PowerMatch with the DUOs though.

Thanks @KickrLin and @tnordberg

Good advice. I think I will do the ramp test with my 4iii on the Core rather than an outdoor test, seeing as that’s how I get my FTP for TR.

Unfortunately my turbo bike is an old 9 speed with 175 cranks and my road bike is an 11 speed with 172.5 cranks, the same as my 4iii crank, so I’d have to keep putting my road bike on and off the trainer rather than swapping out the cranks. I’ll stick my road bike and 11 speed cassette on Core for the ramp test and the erg mode mid-to-longer intervals to work out the difference and then adjust the scale factor on the 4iii.

Thanks
James

Hey,

I thought I’d write a reply now that I’ve experimented with my left crank 4iii power meter and worked out my training zones for my outdoor bike. I’m not sure if what I’ve done is a good way of doing it.

Here’s what I ended up doing.

  1. I put my outdoor bike with the 4iii crank on the Kickr Core trainer.
  2. I paired the 4iii to my Garmin Edge.
  3. I calibrated both the Kickr and the 4iii.
    4, I then did a TR ramp test using the Core ERG power.
  4. I noted down the difference in power from my Garmin/4iii and the TR/Core at each step. My writing became a scrawl the further I progressed.
  5. I worked out my training zones based on my the Kickr Core FTP.
  6. Using Garmin Connect I adjusted the power training zone perimeters based on the difference I observed between power meters.

I found that my 4iii was 15watts higher than the Core at zone 1, 10w at zone 2, 7w and zone 3, 3w at zone 4 and 0w at zone 5 and higher. I’d have to half those watts to find how much stronger my left leg really is as the 4iii doubles the power.

Anyway, if I was doing Trainer Road workouts outside, I think I’d have to do the maths in my head, but I think what I’ve done will work if I want to make sure I’m riding in the right zones.

Thanks
James

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With a single bike, this is what I do. I bought a seperate 10-speed cassette for the Core. It takes next to no time to remove the rear wheel and mount on the trainer. IMO, it’s worth the minor hassle of moving the bike on and off the trainer to be able to use the same power meter for all of your workouts, indoors and out.

The hassle becomes less minor if this requires you to index your gears every time, but I’ve not found that to be a problem.

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Same here. I have 4iiii left side power meter and Kickr Core and I use the same bike in and outdoors. This is the best way to have perfect consistency. I have Ultegra 11 spd cassette for outdoors and 105 for the Core. It only takes 1 minute to swap around and off I go.

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What you’ve described makes sense, and is perhaps even more work than was necessary. As long as you know the offset (achieved by your steps 1-4) of the two power curves you’re in fine shape.

Ultimately if you can use the same power device for both you’re in a better spot, but given you don’t want to swap the bike on and off the trainer what you’ve done is the next best thing

Thanks guys.

I am tempted to get an 11 speed cassette for the turbo and use my outdoor road bike on it. However, my shed/man cave has been a year long project. It’s a small brick outbuilding that I’ve insulated and covered in OSB boards and floor to ceiling shelving to make the most of the limited space, but I have left a space above my workbench for my road bike to hang like a piece of art. It’s the centre piece and it’s what I stare at when I’m trying to get through a VO2 Max interval. I can’t have a blank wall.

Now I’ve compared power curves between the Core and 4iii and adjusted my power zones on my Garmin to account for my left/right leg imbalance I think I can devise some decent intervals to do out on the road that compare to the TR ones that I do on my Core.

Thanks again.

Very similar to what I did, although I saved my data from my Garmin so I could compare post FTP test. I’d recommend everyone do something similar if they have a left sided PM as you can work out if you have an imbalance and adjust the PM. Unfortunately for me there were added complications.

If I remember rightly, the 4iiii read about 10-20 watts HIGHER up to around the 170 watt mark. As it went above this point they started to align until around 230 watts when the 4iiii started reading increasingly LOWER values. Only slight to begin, but from 260 watts the difference started to increase more and more up to 20 watts by the time I’d reached 300 watts i.e. trainer reading 300 watts, but 4iiii reading 280ish.

If I were to use my 4iiii and powermatch then V02 work gets super hard because my left leg is used less and less as the numbers get bigger. In fact, before I got my smarttrainer I failed every V02 max session. Now, using just the smarttrainer I’m finishing them, just.

For me, using the smarttrainer without powermatch is fine as I do most of my workouts indoors. If I’m outside I go on feel when riding zone 1/2. Zone 3 to threshold the numbers are roughly right and then when doing VO2 reps I don’t stress if it’s showing 300 instead of 325 as I know it’s more like 325! I’m happy enough now I know, plus I couldn’t warrant the extra money I’d have to spend to go dual sided!

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My 2c:
I have compared my 4iiii L to my smart trainer (Tacx Neo) and corrected the 4iiii via the app so it reports the same avg power as the Neo.

Now I can use the Neo indoors and the 4iiii outdoors with similar intensity.

Need to validate the multiplicator from time to time, that’s all.

@Agglo, I’m running the same set up. Out of interest, what correction factor did you calculate?

My 4iiii was reading considerably high, so I set it to 0.9 which works well for now.
Not perfect, but on average it matches my Neo to 1%.

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I considered adjusting the offset, but like @lebowskii98, the figures are accurate at threshold and not elsewhere. My right leg becomes stronger over my ftp too, but luckily only by a couple of watts.

My garmin power zones are now 25%, 60%, 80%, 90%, 105%, 120% and 150% from Dr Andrew Coggan’s 25%, 50%, 75%, 90%, 105%, 120% of FTP. Instead of guessing if I’m riding in the recovery zone between intervals I can see what zone I’m in on the Garmin. Though that means even more data fields on my garmin display to get my head around and it might be best just to guess.