Indoor and outdoor FTP test?

Hi team,

I changed my resistance on my Kurt Kinetic trainer ( had to maintain it and forgot the settings ), AND switched from virtual power ( FTP was 225 ) to now a Power2max metre, and my new FTP is 60watts lower than before.

I’ve seen a few forum posts about indoor vs outdoor numbers, and my most recent FTP test ( today ) was pretty accurate, I tapped out when I couldn’t hold the numbers any longer.

My question is, how can I translate my ( lower ) FTP to outdoors, and is it even worth it?

Maybe I could try the 20 minute test over the ramp test?

There is no formula, its very individual, yes outdoor power is normally higher but not always, sometimes some people find maintaining power indoors easier. So the bottom line is if you are serious (and if there is a discrepancy) maintain a log of indoor and outdoor power separately. Then use each one for individual zones in each setting. bw AG

Are you using the same power meter indoors and outdoors?

Typically we recommend testing indoors and using that FTP you earned both indoors and outdoors. Most people do not have drastically different FTPs inside and out as long as you use the same bike, with the same position, and have proper indoor ventilation.

If you feel like your power is drastically different, you could do either the 8 or 20-minute test both indoors and outdoors to see what your true offset is. If it is very high, then it may be worth translating, but it is important to keep in mind that power meters typically have a +/- 3% accuracy. So unless you have more than a 10-15% difference, it is not going to have a major effect on your training.

I think this raises a good point.

For my outdoor rides, I use a left crank power meter.
For indoor, the TACX Neo, which I have been led to believe is pretty much as accurate as power meters get.

My FTP measures about 10 W (~5%) higher outside and when using both on the trainer. One could assume that both are fairly accurate and I’m losing that through the drive train (or a slight imbalance).

It would be an awesome feature to have the ability to weight outdoor power to 95% so that I don’t have an inflated TSS!

my advice is to do at least 1 outdoor test close to the indoor one in order to understand the % difference between the 2: in this way you can, in the future, only do the indoor test and change the outdoor one accordingly.
obviously it’s always better to do an outdoor test every few months

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