FTP Indoor vs outside road

What are the differences you are all seeing between your indoor FTP and outside road?
I did the 20 minute FTP today. My best comparison would be my avg power on outside rides.
I didn’t find the Ramp Test very accurate.

I have a Kickr smart trainer. Today doing the FTP test (not ERG) during sections of the 20 minute test my resistance would get very easy (a drop of 60-70 watts) without me shifting or changing my cadence. They only way to get the power back up was to shift into a hard gear and shortly after go back to my typical gear. Has anyone else experienced this? Does anyone know the cause?

Thanks for any input

I’ve had my Kickr do that once or twice and I had to reboot it to get it working again.

Wheel on or direct-drive (wheel off)?

On my 2017 Kickr direct-drive, the only time I’ve had weird resistance changes was due to shifting lighting (sun bouncing off light concrete flooring in the garage, and shadows from overhead lights). Except for the original gen1 Kickr, Wahoo uses an optical sensor to estimate power. Putting a black mat on the concrete floor resolved the problem. That was suggested by Wahoo support, and it worked.

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I think most folk see there outdoors FTP higher than indoors. I don’t because I am too much of a wuss outside, whereas on the Turbo I can switch off to the outside world and not worry about traffic, staying up right etc. Outdoors, I’ve only ever matched my indoors FTP occasionally and I am usually below it :joy:

Please share a link to your test, if your account is public. Something sounds off and may be best reviewed by TR with their log access, but maybe we can give some insight with more info from the test.

Loss of resistance, while in Resistance or Standard mode seems odd. I have experienced resistance drops as a result of power data drops, but that is in ERG mode, and I would not expect that in RES or STD modes.

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Not in answer to the trainer issues, and I’ve only done a few, but a ramp test (indoors, obviously) always gives me a value c. 5% higher than the 20 minute method indoors. My outdoor 20 min test and my indoor ramp match up pretty nicely.

I find indoor is way more consistent and much easier to hold power. Outdoor has dips and things like wind. Resistance spikes and recoveries throughout.

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I have found a quiet piece of road, where I do all my longer intervals and TT efforts. That is also my FTP test track, and I like riding outdoors just so much better. If the road is good enough (no too sharp corners, no downhills, no traffic), there is no reason to be able to pace an indoor test better. However, I do understand that an indoor test is more convenient.
My coach gave me the following advice:
If you plan to ride outdoors mainly in the near future, to your test outdoors, if you plan to ride indoors mainly, do your test indoors. It is easy to extrapolate the power zones from that, that are pertinent to your training. My indoor FTP is usually 1 to 2% lower than outdoors. For harder efforts (especially sprints), that gap becomes even greater.

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I haven’t done an outdoor FTP test before but have done a fair amount of outdoor workouts and I find my FTP to be about the same in both as long as cooling isn’t an issue.

Many times I find efforts harder outside but I think that has more to do with sitting in a slightly more aero position on the bike and adjusting to all the pitches.