FTP Increases and indoor vs outdoor results

In your experience, does it make sense to be able to see a 27-point gain in FTP after 8 weeks of training? I don’t have any good way of calibrating my trainer so I’m just not sure. I’ve been doing 3-4 hours a week on a zwift structured plan.

The reason why I question it is because I did a ride of similar mileage outside and it took me 15 minutes longer and had a thousand feet less of elevation. It was a cold day (28f) and the resistance is certainly much higher outside even on a regular day but certainly in the cold, so that may account for the difference but just wanted to be sure.

Outdoors I covered 32 miles and 1900 feet in about 2:15 - Avg HR in the 160s
Zwift was 33 miles and 2900 feet in 2:00 - Avg HR in the 150s

I don’t have a power meter on my bike


I don’t think you can compare the in door vs out door performance.
I think zwift tends to exaggerate road speed.
If your FTP has increased it can mean 2 things.

  1. you may have learned how to perform a better FTP test and you score went up because you applied you fitness in a more efficient manner - there is an optimal way to do a test and that optimum will vary between riders and vary between days for the same rider.

  2. You actually have improved your fitness. Even though you were slower that your Zwift self, you are probably faster than you would have been other wise.

This year, I’m going to lay out a flat course in the country and try a few real life FTP tests on strava and see how I do. I won’t have an accurate power but I’ll have speed HR and distance / time.