Indoor Vs Outdoor FTP



Hi guys,

Does anyone find a big discrepency with their indoor vs outdoor ftp? I did a 40km ITT a few weeks ago and held an average of 290 Watts for 1:03hrs. Theoretically this gives me an FTP of 290W (maximum sustainable power for 1 hour). However, when training indoors I find it difficult to hold 240W for a 10 min interval (I did the ramp test today and scored 238W). Both indoor and outdoor were measured on the same powermeter (Powertap P1 pedals), and both were done holding the TT position for their entirety. The only thing I can think of is heat exertion (I have 2 fans going indoors but still sweat quite a bit).


Good work on the 40km ITT dude!

Personally what I’ve found is when I’m running my Kickr on erg mode and I’m in small ring front and up in the 20’s on the back, it lacks some momentum turnover and therefore the pedal strokes are more taxing and could lead to the difference in FTP’s.

Tbh I’ve never tested FTP outside so I dunno how applicable what I said is.

Hopefully someone more versed in this area can shed some light.


TR did a blog post about it here:

The differences between your indoor and outdoor power do seem pretty large though! Have you tried the old style of tests? The 20-minute one might be closer than a ramp test due to similar types of effort (long maintained vs short high power)


If you have a power meter I’d definitely recommend doing one outdoors :slight_smile: . I usually use the big ring and the middle of the rear cassette, but gear choices definitely make a difference. I have always tested lower indoors, usually about 30-40 Watts :thinking: but at the same time, if the workout is hurting, i know the gains will pay off outdoors (i do 3 out of 4 of my weekly rides indoors)


Thanks for that blog! Ive done both tests (ramp and 20 min), both usually yielding the same results. I’m not too fussed though (more just curious). As long as I can push the watts outdoors i’m happy (I dont really do zwift racing for this reason)


I may be one of only a few who can hit watts more easily indoors (mainly thanks to erg mode). I’m not sure what my outdoor ftp even is, I just don’t have the discipline to do intervals outside, I’m pretty sure my watts aren’t really any higher outside though.


Yeah Zwift racing seems daft to me unless you have some way to ensure riders are the weight they say they are, which is pretty much impossible!


I think I’m pretty lucky. The TT’s are usually close to my house so even a 20km TT will be enough to get an estimated outdoor FTP. I’m similar to you, I have never done interval training outdoors as thats more for me to enjoy the ride. But if you can find a nice long straight road it’d be interesting to see what you get :slight_smile:


Yeah thats exactly what I think. Theres also the problem of calibrating the power meters. The first Flux I had overestimated the power by 15-20 Watts (I’m on the Neo now which reads the same power as the P1 Pedals, so I’m happy with that).


I have exactly the same set up (Powertap + small ring front on trainer) and exactly the same results ! Huge difference indoor vs outdoor. BUT, I also found that when my FTP increase inside, it also increase outside on the road. Just make sure to have two specific FTP (in vs out) to do your workouts at the right intensity AND have right values for TSS, CTL, etc.


Zwift racing is great, as long as you go in with the right mindset. Recognize that you most likely won’t “win” the event. But you CAN win for your own personal goals. Use the riders (proper setup or doped) as rabbits to chase and play with in the event.

You can have a ton of fun and really challenge yourself by simply looking at it as a challenge and the chance to push yourself while riding inside, in a similar way as chasing your buddies outside.

Ignore the fliers and just focus on your own effort and what particular performance or fitness goal you set for yourself. I usually start hard and try to latch onto the 2nd group. Play in the draft and just have a good, challenging ride.