Indoor FTP vs outdoor FTP

Hi, Im into week seven now after committing to a Wahoo Kickr purchase and getting a referral from a friend. It seems that by using the program set up for requirements my FTP is lower on the trainer using erg mode than it is whilst out on the road. My question is should i do a separate FTP test on the road (which would be the 20 min test) and use this to work out my zones whilst i get that much needed break from the pain cave? Cheers for all the enthusiastic work you guys do.


Yeah - I always fund a 5% to 10% difference. I’ve read that oustide your body handles heat much better (wind) and that the air resistance does some of the work of holding up your upper body for you, but indoors you expend more energy holding your neck and upper body up which isnt counted toward your FTP since that is a pedals only measurement.

I echo those feedback comments.

My own personal experience is that indoor FTP needs to be separately established to set your indoor training zones unique to the setup you are using.

Mine was consistently about 7%to 8% lower than what my power meter registered outside, a couple of time as much as 10%.

This general point appears from my observations on this forum to be fairly (but not in everyone’s case) common as an experience.

There are likely to be a wide range of possible single and combining reasons for this, all of which will depend to some extent on your individual and personal set up and circumstances.

Examples cited in many places on this forum include: different power meters / indoor temperatures / erg mode versus outdoors effort differential / position and many more besides.

Can be easy to fall into the trap of over thinking this. Easiest approach is to test using the exact setup you will use to train with and accept those results for specific use in that setup.

If it is different to what you’ve seen outside them so be it; it doesn’t matter as you are simply setting your zones applicable to the specific environment and setup you’ll be using for training, so don’t sweat the numbers, instead focus on the process.

NB: there are numerous threads worth reading on here that compare and contrast the different types of ‘test’ and which might be best to select. The search function is your friend in this regard! :grin:

Again - a big risk of over thinking this. Chose one you are familiar with / prefer / are prepared to be willing to repeat over time and see how you get on. Many use the ramp test. Others prefer the 20 minute test. It seems fewer elect to use the full 1-hour test.

There is a commonly referenced perception that if your past riding history and limitations or natural preference and / or innate biology favours higher end shorter efforts then there is a consequential possibility the ramp test may slightly over-state your FTP and so slightly skew your set zones as a result.

I have no idea if this is correct (in theory or in practice) however I’ve observed it does come up a lot in discussions on this forum.

One tip I’d offer is don’t fall into the trap of making preparations and / applying approaches or tactics during testing that you won’t replicate on training.

You’ll do yourself no favours in that regard. For example, If you decide to fuel your body in a totally different way ahead of a test and wait for the ‘perfect’ time or how you feel (whatever that means for you) to do a test; with the aim of maximising the number you hit, then unless you can consistently replicate those preparations during each of the sessions that follow you’ll be setting yourself up to potentially fail.

Better to have a slightly lower number, leave your ego out of it and then go on to be able to adhere to the workouts to a much higher level of compliance - this type of consistency will serve you much better in the long run.

Hope this helps

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I am on the fence about buying a power meter (Assiomas).
Because of family and work constraints I do most of my riding indoors. I decided on a Tacx Neo 2T last year because I can just hop on and get going, no faffing about required with calibration et cetera. I am really happy with the Neo and I am kind of reluctant to add a new layer of complexity to my setup with a dedicated power meter. I know I will start worrying about power discrepancies between the trainer and the pedals and then this thread made me realize I will also also have to deal with indoor and outdoor FTP.

I am not a crit racer and I don’t get to ride outside too much atm (maybe 15 rides/year) but I would love to do some longer semi-competitive events in the future (like Mallorca 312) and I guess it would be great to have power data for pacing. That would require an accurate outdoor FTP setting, though.

Where I live I won’t be able to do an outdoor 20min or ramp test. There is only one climb in my area wich takes me around 12-13 minutes. should be able to calculate FTP from a max effort on that climb, no? Although I’d have to ride to that climb first which takes around one hour. I guess a quick break and a gel before the test would still allow for a useable result?

What would you guys recommend? Am I overthinking this?

You may not see much difference between indoor and outdoor, I tend to believe doing a longer 30-70 minute test will give a more accurate FTP that is good both inside and outside. At least for me that has been true, and I’ve setup my Kickr and gearing to get indoor and outdoor aligned.

Even if there is a difference just focus on indoor training, and use the outside power meter for post-ride data and NOT pacing unless you can determine the difference (if there is >2-4% difference). The key is doing the same test inside and outside, so if you can’t do an outside 20-minute test then doing a 12-minute indoor vs outdoor sounds like one way. Or doing an 2x8-minute test.

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I’ve basically given up on any sort of indoor ftp or ramp test… In the past, my outdoor TT race efforts have ranged between 375- 400W. However, anytime I do a ramp test, my estimated ftp is normally 315 - 320. This seems odd, since I have done some sustained 300watt 2 hour efforts on my trainer the week after my ramp/ftp test. So, I’ve thrown in the towel on testing indoors! This has been an issue for me over several years. Hopefully, the new adaptive AI training, when released, normalizes this discrepancy.

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