Much greater power indoor vs outdoor power

Hi All

I have the following problem: I can produce significantly more power indoors than outdoors.
That could be between 30-50 w on a sustained efforts of duration say between 5min to 60min.

I am using 4iii for outdoor and tacx neo s for indoors. I compared them indoors and the difference in readings is +3% on 5, 10 and 20 min (that is it tacx shows around 5w more in avg) but that’s not even close how much less I can produce outside.

My hypothesis is that since riding indoor for a longer period of time (whole winter) I got used to the feel of the tacx trainer freewheel and simply I can more effectively press pedals on the home trainer.

My worry is that all that gains that I obtained riding indoors are close to useless in a real world.

Does anyone has a similar experience?


I would definitely start using Power Match if you have power meter on your bike that you use on the trainer, if its the bike you also use outside.

Its not uncommon for things to differ.

Do you do a power meter calibration before riding on your bike and/or trainer?


Actually the difference between the powermeters were more significant, but then I did some reseting and calibration on 4iiii and seems that it got closer to 3% on the last testing which I guess is acceptable.

Still my main concern is that a sensation of grinding that power with a freewheel of a bike trainer appears to be easier than grinding the same power against the asphalt. I don’t how to explain it but on the freewheel I can produce more constant pressure even or smaller cadence for a longer duration of a pedal stroke. Outside similar power would require much higher cadence and it would be more “spiky”.

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What gearing are you using on the trainer? It sounds to me like you might be in a lower gear. That would equate to a slower flywheel and lower inertia which would feel more like climbing. While outside on the flats you have a much higher inertia which can feel more ‘spiky’ at the pedals as opposed to the longer pressure of climbing.

Maybe try riding in a higher gear on the trainer if that is closer to your outdoor riding. You’ll probably adapt relatively quickly and not lose any power between inside and out.

One thing to add though is that high inertia of the flywheel can make the trainer feel easier, but I am wondering the effect of this on trainer training.

I understand that a watt is a watt, but for some reason it almost feels like cheating…

With higher inertia, it feels like you pedal less of the stroke, even if you’re putting out the same power.

You are pedaling for less distance around the stroke but you’re peak torque is also higher. So you get the same wattage out of the other side of the equation. It’s definitely not cheating but it’s just different.

Also, if OP is in a low gear like it sounds like then they’re feeling it as the opposite. They can do 40W more at the lower inertia which is a HUGE difference. But if a majority of their riding is fast on the flats then it doesn’t make much sense to only train indoors with a low inertia.

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Yeah, makes sense, hence why I just said that it feels like cheating.

I usually do smaller gears inside due to vibration. And with bigger gears I can even feel the vibrations in my feet and its horrible…

Actually in both cases very similar gearing 50 in the front and then at back around middle of the cassette 11-32

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I would get this problem with old (not smart) E-Motion rollers. Mag setting on 1 was most road like, but still a high inertia environment. too much roller time, not enough road time, and I’d end up getting high power on the rollers because no wind, no road surface, just 95-100rpm smooth power.

When I got back on the road things would start to even out. Watts is watts.

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Hmm, having never used a Tacx like yours I can’t say for sure. Also, remember that the flywheel on the trainer is maybe 15kg or so while you and your bike are like 70-80kg. So even if your trainer speed is the same as outdoors the inertia will be lower inside. But I’m almost certain that that difference will become less as you get used to outdoor riding again. The neural firing is different enough that it can take some time to adjust.

Are you using erg mode inside? It could be that you are just able to put out more watts when the only thing you have to focus on is pushing the pedals.

I think there are a ton of variables to consider

  • different power source
  • having to focus on the road/traffic
  • temps (maybe you’re well cooled inside and then wearing a warm jacket outside)
  • small coasting or letting up as the terrain adjusts

But I wouldn’t overthink it. If you start to ride outside more and the difference still exists after several weeks then it might warrant further investigation.

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Indeed, I hope it is just a matter of time, and getting bit more accustomed to the road.

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I have the same problem, and for me it’s usually down to the variability of the road versus the stability of my trainer. For example, my last two rides, one was 90 minutes outdoors, trying to ride 60 minutes of steady TT effort with 1,000 feet of climbing and wind. The other was 60 minutes of sweet spot indoors. Looking at my time in zones, ride 1 has 8 minutes in zone 7 power and almost 20 minutes in zone 6 power, along with about 15 minutes in zone 1 or 2. Compared to my indoor ride which had no zone 7 and only about 30 seconds in zone 6. Both rides were 202 NP, indoors was 187 AP, outdoors was 182 AP.

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With a bit of focus I’d bet you could tame most of the road variability, unless the roads have really steep pitches.

i have a similar problem, and wondering if it will make a difference to adjust my indoor FTP(10-15%), to compensate for the outdoor low Wattage experience, BUT decrease the training time by 15mins?

I’m generating much more power outside. About 20% more. Which is a fairly significant difference. I’m working on testing the outdoor power meter (Garmin Rally XC200 pedals). There’s a procedure that involves hanging a weight of known a quantity and seeing the pedals give an right response. But I’m fairly convinced at this point that difference I’m seeing are really due to differences in power I’m asked to generate and when. Intervals workouts in TR tend to way less dynamic that then the trails I ride outside. The terrain is constantly changing. I would think there would be a way to take the elevation data from strava, and have a kickr emulate an outdoor ride? It would interesting to see I did the same ride inside that I just did outside (adjust for other factors, a big one being rest), and see if power is closer. The outdoor ride also includes significant rest at points.

30 watts at 300? or 150? Delta could be anywhere near 10%-20% depending on what the efforts are.

Regardless, I have a few theories which may all be dumb ideas and I’m sure you’ve considered most.

  1. Your technique outdoors may need work. Indoors the bike is fixed, outdoors it’s moving around under you. There’s more core and ancillary muscles that have to be activated to control the bike. This may affect your overall output

  2. My RPE with a headwind makes it harder for me to produce more watts than my RPE with no/tailwind. I don’t know why but it’s easier for me to push more power sans wind.

  3. You struggle with the variation in terrain.

  4. Single pedal power source. Your stroke indoors is closer to even, outdoors you favour one leg over the other, the discrepancy is doubled (ie power source is 5% weaker, number is doubled, gives it 10% delta.

  5. I have no idea why but outdoors my position on the bike is significantly different to outdoors. If this is the case maybe it affects your output. Are you more upright on the trainer? Are you using more glutes there or hami’s vs outdoors?

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