Outdoor vs indoor FTP

Hello all.
Today i ve done my 1st ride outdoor with a mtb powermeter. Until now i had done trainings indoor with a tacx neo and outdoor trying to follow RPE. Today i was going to perform the excercise i had planned for today (Carter), but instead of that, i did a 20’ ftp test to see if there was any difference between indoor and outdoor ftp. My surprise is that its a massive difference. My indoor ftp was calculated as 219 doing the ramp test, and outdoor today was 275 doing a 20’ test. So i would want to know what to do. Repeat the indoor test with a 20’ test? adjust outdoor excercises to outdoor ftp? keep for indoor excercises the outdoor ftp?

Thanks in advance

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ups, no reply?

Normally you will be have higher power outdoors as moving through the air and wind cools your body more, especially in the 20 min test.

Your numbers are 25% higher and that is way more than can be attributed to cooling. It seems something is off with your power meter or your trainer. Anytime there is a discrepancy of more than 5% you should investigate the equipment.

How far apart were your tests of 219 and 275? If they were months apart then you gained fitness and a lot of it. If they were close together, again, investigate.

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Hi @Rc213v

I have pretty much the same “problem”.

What did you do with these discrepancies? Do you use TR for outdoor workouts?

Vanja

Assuming the 20’ minutes test outside was done correctly - and I have no doubt about that - and also assuming your powermeter worked correct: Yes, of course. Do your outside workouts based on the outside FTP. Absolutely. It’s absolutely no surprise (actually quite the norm as far as everything I gathered over the last years) to have a higher outdoor FTP than inside. The difference may vary. From person to person, from equipment to equipment and also from how used you are currently to indoor training (i.e. are you right at the end of a months long period where you had at least 2 indoor rides per week or did you do indoor rides only every now and then).

But for some or most - there will be a difference now matter how advanced your trainer model is and how often you are sitting on it.

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Hello there, Interesting subject, for me the opposite happened. Until now I only rode outdoors and my most recent FTP test (uphills) 20min showed about 245watts. Now I got an indoor trainer (elite suitors) and I did the ramp test which gave me 195watts, quite disappointed. I am wondering if I could have lost so much power in a couple of weeks.

The way I see it there is a contribution of two factors:

  • Outdoor power is usually higher than indoors.
  • Different test protocols. Probably you are better at sustained efforts than at V02max.

You might have a point there. I am new to the indoor riding and I think I will use the indoor FTP for the indoor training and the outdoor FTP (will do a new one as soon as weather allows) for the outdoor training. After a couple of weeks I will test again to see if there is an improvement in the indoor FTP, for the outdoor FTP I don’t expect any improvement.

Is there a way to set up 2 FTP values – one for indoors and one for outdoors? Or, how should we go about doing something that achieves that effect?

Here are a few basic things to try and improve your indoor space:

  • https://www.trainerroad.com/blog/best-indoor-trainer-setup-for-your-budget/

  • Probably most import, is the cooling aspect. Make really sure that you have sufficient air moving over your body. Many people ride with no fan, or one fan that is not really effective. Many of us have settled on at least 2 of the high flow, blower style Lasko Performance fans. I run 3 total on my hardest workout, with cold air pulled from a window ducted right into two of my fans. I can hit power numbers right in line with my outside riding, and this cooling setup is a key part of that.

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  1. Put your pedals on your trainer bike and compare values of both sources. Pedals can read a little higher, because there are no drivetrain losses. If there is a difference calibrate both.
  2. Did you get close to your max HR during ramp test? If not - push harder next time.
  3. If you did the outdoor test on a hill: Different muscles are involved and i think you can push harder going uphill.

A couple of points here:

-Are you using data from the same power source? So are you using power matching with the trainer to get power data from same power meter as used outside?

-Was 245W computed as 95% of your max 20 min power climbing outside? You should also do an all out 20 min test inside if you want to compare outside performance with inside.

-Have a look at gearing while on the trainer in ERG mode. The gear you choose will change the flywheel speed, which changes the way the bike feels. Climbing is more like slow flywheel, while riding on the flats is like having a faster flywheel. However, given you have a fairly light flywheel (3.5 kg), you might need to choose a fairly big gear just to mimic the feel of climbing.

  • Powermeter: I used the Powermeter on the Elite Suito trainer and I also used my powermeter on the left crank + record with Garmin head unit. There was a small difference, maybe 3 watts

  • outside was 20min and 95%

  • inside was trainerroad ramp test 75% of last sustained minute

  • I was unsure about my indoor power, that’s why I used the ramp test. If I had used the 20min test then I would target too high power and be exhausted before the end.

Gearing: I used erg mode and my preferred cadence 85 to 95 similar to outdoors climbing for the ftp test.

My plan is to practice indoors with the indoors FTP and after some practice do a 20min FTP test.

In the end it doesn’t matter much as the weather where I live will give enough opportunities to ride outdoors. The outdoor I used outdoors FTP

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Ok, so power meter is not the issue. It is possible the ramp test falls low for you but this difference is too large,

Try using a heavier gear, use still your preferred cadence, and see if you get better results from the ramp test.

Using a higher flywheel speed allows you to push for longer in the down phase, making it more like outside .Otherwise your smaller muscles need to produce more force than they are used to outside, during the other parts of the pedal stroke.

Hi Mrpedro,

That is a very good suggestion you gave me there. Using a higher flywheel speed. Because I remember on some steeper outdoor climbs (more than 15%) I usually run into a similar problem, I can’t sustain my usual power, I always wondered why. I will give it a try, Thanks👍

While @mrpedro could be on to the right idea, I think there’s more to it when comparing to riding up climbs if that’s what you were thinking. One major difference I always notice is the (lack of) cooling of my body when going up climbs. Depending on power, power-to-weight, environmental factors, etc., going 5 mph provides far less evaporative cooling than going 20+ mph. When those climbs are long enough I notice a lot more sweat collecting on my skin than if I were on a (relatively) flat section because of the lack of airflow across it. There’s also the shift of body weight, how that weight shift affects the pedal stroke and muscles used, cadence limitations, and probably more things going on.

I am not sure about the climbing. I also heard/read that during climbing (on the road bike) the FTP can even be higher than outside and flat. I never did an outdoor flat FTP test, but my results are:

  • Indoor: 335 W (Ramp Test)

  • Outdoor (Climbing): 360 W (2x8min @ 400W)

BR

Been on TR for 4 years and for most of that time my outdoor/indoor FTP was very consistent, using the same stages PM in/out. A few months ago I changed out my bike indoor (same trainer, pm, and fit, different tire) and since then my indoor workouts are WAY harder than outside. Doing them at 100% is much harder, and getting to a similar RPE I feel I need to lower resistance by at least +/- 10%. To be clear, I CAN do the workouts outdoors - and feels appropriate.

My only other data point is my gavel bike has a different Stages GRX PM. It used to be similar to the other stages, maybe reading a little high, but now seems to read much higher outside.

I have tried everything indoors – different devices, versions of the app, spin downs, deep spindowns, resetting the PM, using wahoo app to link PMs, using powermatch. Trying different gearing. Been working with TR support (They have been great) for months).

Any ideas?

I was just writing from my experience about the lack of cooling on steeper climbs. I cannot find a section of road to complete a 20 minute test on near me so I’ve always resorted to doing it indoors with 2 powerful fans pointed at me. It was just based off the training rides in Tempo or higher outdoors.

Fascat recommends a 2-3% climb for the test, more than that can lead to cadence issues from their blog about it. I know when I’m doing a 10% climb I’m going pretty slow, around 5-7 mph, and my cadence is lower than I’d like, around 50-60 rpm. There’s a big difference from those 10% (or steeper) climbs to a 3% for what I’ve experienced in terms of cooling, cadence, etc. Perceived air temperature goes up along with seeing the heartrate climb then reduce once the steep section is over. Not 10 bpm but 2-5 bpm.