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FTP test using Zwift and 4iii trainer - Should indoor and outdoor FTPs match? Is 4iiii accurate?
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Hello,

I just performed the 70 minute FTP test on Zwift. The test with the long warm up and 20:00 FTP test toward the end. My FTP increase by 24 watts from what TrainingPeaks had it from my last field test. Zwift made the automatic update and TrainingPeaks sent a notification recommending a new FTP matching Zwift. I'd appreciate some thoughts on having different FTPs on the trainer and road. I need to make a decision on accepting the TrainingPeaks recommendation and moving both my indoor and outdoor FTPs from 214 to 238. I know this is not a life and death matter but I'd like to get it as right as possible.

Also, does anyone have any experience with the 4iiii trainer and its power accuracy? I tried to run my Powertap pedals and the 4iiii power measurement at the same time, but I'm not that tech savvy. DC Rainmaker was not a big fan but I've grown to like its quietness and keeping the rear wheel on my bike at all times.

Thanks!
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Re: FTP test using Zwift and 4iii trainer - Should indoor and outdoor FTPs match? Is 4iiii accurate? [Slow_Nole] [ In reply to ]
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I wouldn't do any adjustments based on the 4iiii trainer. It's just not accurate/consistent enough.

Typically your indoor trainer FTP is lower because of less efficient cooling indoors and because the measurement is taken further down the drive train (so the power lost to things like chain friction aren't counted).

ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)
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Re: FTP test using Zwift and 4iii trainer - Should indoor and outdoor FTPs match? Is 4iiii accurate? [Slow_Nole] [ In reply to ]
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Different power meters can result in different numbers.

Unless you had them overlaid ( eg 4iiii in zwift plus your powertap pedals on your garmin head unit ) and directly compared the numbers, you could be looking at apples and oranges.

I suggest figuring out how to use powertap pedals as both your indoor and outdoor power source, and only use that.

Power numbers from the 4iiii trainer are basically useless if you already have a power meter.
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Re: FTP test using Zwift and 4iii trainer - Should indoor and outdoor FTPs match? Is 4iiii accurate? [Slow_Nole] [ In reply to ]
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Just throw the power meter on the bike used on the trainer and repeat the test in a day or two.

I tend to just do a hard 20 minute effort within a zwift race and use that as an approximate value then reduce it by .95 , close enough.
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