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.

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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.


I am in the same boat. I have an indoor ftp of 248 (4iii left crank and elite dumb set of rollers, tested around december). Last week I did a climb in Calpe (Spain), full out. I averaged 302watt over 20mins. So that gives me a ftp of 286. Gonna do a ramp test in a few days to see what happens but i can’t imagine such a huge bump. Anyway i will keep you updated.

Should I now update my latest outdoor rides with that ftp and use that ftp for outdoor rides?

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It can be many different factors affecting this. Last year I estimated that my FTP was about 35Watt higher outdoors than indoors. I used to train in a very cold room without a fan, and I am pretty sure that overheating played a big role in this discrepancy. This year I ride indoors with a fan and the gap seems to be much smaller - although I didn’t test explicitly outside yet.

Fascinating topic.

I think mine are identical. Maybe higher indoors if anything (I can’t do my FTP for 35 minutes in an outdoor TT).
I have a big and small fan indoors. We have a cold house in winter. All doesn’t make a difference.

I’ve got a fairly large discrepancy as well (~35w), i’ve come to be OK with it, i figure out from outdoor rides what my outdoor FTP is anyway. The biggest issue I have is outdoor rides overestimating TSS in relation to their indoor counterpart, so my CTL/ATL ends up super wonky.
I’ve done multiple tests indoors vs. outdoors and always the same result, it’s not a ramp test thing.


That would be annoying. This is making me wonder now if my outdoor FTP
is lower than my indoor FTP as I can’t get close to my indoor FTP in
races (same power meter). I have never done an outdoor FTP test. It
sounds hard to arrange.

outdoor and indoor FTP’s are normally different: sometime very different, 10-15% (mine is 12% less)

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So, What is the science ….

If we can push 20+ watts harder outside vs inside when we are doing our work inside at lower levels are our muscles being “pushed” enough to adapt/ grow?
I can ride 230 watts for an hour without a problem outside. Inside, I have to focus and take it seriously to hold it for my SS intervals.


I do not think it’s just a mental thing but rather a physical matter: indoor there is a greater energy loss due to the dissipation of body heat; only this “steals” several watts to the performance

so yes, muscles are pushed enough … the important thing is to use two different FTP depending on where you train

Hello guys. It is an interesting topic. Few days ago I made a. FTP test indoor on my direct drive trainer. I measured the effort with power meter and with a smart trainer. I train without a fan in a hot room. 23-26C. I hit on the test 321w. That is 4.5w/kg for me. Approximately what would be my ftp outside?
Thanx for the answer