The phenomenon of FTP determined by 4DP on a trainer generally being lower than that determined from 20 minute intervals done outside has been well-covered in Sufferfest articles. But I thought that it would be interesting to share my own experience with this and see what others have experienced.
I started using a power meter last year, using a free subscription to Training Peak and the open source Golden Cheetah software to analyze my rides. I found a reasonable stretch of road to do a conventional 20 minute FTP test and returned to it several times during the season. The very first test put FTP at 190, which improved to 210 around mid-season and settled at 200 as the cold weather set in. Golden Cheetah’s “extended CP” model gave similar estimates.
I then started using Sufferfest workouts in ERG mode on my newly-purchased trainer. My first FF set my rider type as Pursuiter with FTP as 181. After completing the 12-week All-Purpose Road plan and the ToS, a second FF showed no improvement in FTP, but did improve NM and MAP, still a Pursuiter. Following a further 6-week Power Builder Program, a final FF showed FTP improved to 187 and rider profile changed to Sprinter.
I’ve been riding almost exclusively outside in the three weeks since the last FF and today tried the 20 minute FTP test for the first time this season. Subjectively, the experience was challenging, but not quite as draining as I remember from the final attempt last year. Nonetheless, Training Peaks estimated FTP at a personal best, 222. Golden Cheetah gives a similar estimate.
The main take away message is that the Sufferfest programs work to improve performance on the bike outside, both subjectively and as measured by other algorithms.
It’s not necessarily lower in 4DP. They’re both trying to estimate the same thing; both are consistent in that the approaches accept a standalone 20 minute effort doesn’t equal ftp, but one discounts it with a multiplier and the other “discounts” it via test design.
I’m currently training indoors only - Suf All Purpose plus a bit of rouvy and zwift.
I haven’t tested but I’m definitely getting fitter indoors but my best efforts indoors are still short of my outdoor PBs. So good to hear your experience. Hoping mine will be similar when I get back outside.
One worry I have is that I’ll have gained power at higher cadence/in the saddle but lost power at lower cadence/out of the saddle.
Thanks for the feedback. I think that what is encouraging is that although these are different “yardsticks” improvement in one seems to imply improvement in the other, even if the absolute values are different.
I really like the Sufferfest workouts too. Are you using the same power meter to determine FTP inside and outside? I just did a comparison over the weekend. I used a Wahoo Kickr snap and Assioma pedals. Both were calibrated just before doing full frontal. FTP using Kickr data is 219 and Assioma FTP is 245. Of course I believe the higher number I started using Sufferfest back in November. I was at 176 (using the Kickr). So, either way my highest FTP. Annoyingly, a huge difference between the to power meters but now I know my ranges when I’m riding outside.
Now that’s interesting. I am also using the Assioma power meter (the Uno) outside, synched with a Garmin Edge 130. Inside I am using a Wahoo Kickr, but did not simultaneously have the Assioma synched with the Garmin. I had some issues with the Kickr dropping the connection with the app early on and so have kept the wireless environment as simple as possible while on the trainer.
When I ride outside I always do the “Calibration” when prompted by the Garmin. But, as a review of the Garmin that I read somewhere pointed out, the term "Calibration is misused here. What is happening is actually a zero offset and not a proper calibration to a known reference.
So I guess that there is an additional take-away from this experience. In addition to the various reasons given in the Sufferfest article about why indoor and outdoor power levels can be different, we would have to add the caution that such differences may also be due to using different power measurement devices.
Yes, thanks for pointing that out. It really isn’t a calibration. I was surprised by the difference I am seeing between the two. I would much rather them be exactly the same but as long as I know I can adjust inside vs outside.
I’m currently training indoors only - Suf All Purpose plus a bit of rouvy and zwift.
I haven’t tested but I’m definitely getting fitter indoors but my best efforts are still short of my outdoor PBs. So good to hear your experience. Hoping mine will be similar when I get back outside.
One worry I have is that I’ll have gained power at higher cadence/in the saddle but lost power at lower cadence and out of the saddle
I started using Sufferfest back in November. I was at 176 (using the Kickr). So, either way my highest FTP. Annoyingly, a huge difference between the to power meters but now I know my ranges when I’m riding outside.