My zFTP has just taken a massive (~30w?) jump, despite no performances justifying that.
My zFTP is 314w
My 20min is 302w
That 20min max was set a week before my zFTP jumped.
If you just had a 5 minute PR expire after 90 days, that could explain a zFTP increase. Set a new one and watch zFTP go down.
Thanks for the suggestion. I’ve only started using Zwift again on 30th Dec after a long break, so I’ve not had any PBs reset as they are all less than 90 days. The most recent 5min PB was on 5th March.
I’ve seen a rider in my club mention how he’s now in A, and looking at his ZwiftPower, he didn’t do anything to get into A, so thinking maybe his zFTP has also just jumped up.
I just don’t understand how my zFTP is now the same as my 15min max, which was set 2 days ago!
Nothing has been shared about any changes as far as I know, so if that happened there is no official information about it.
My zFTP seems about the same as I recall though I haven’t tracked it closely. PRs are all from Dec/Jan timeframe.
It’s possible that the answer to your question lies in the shape of the power curve and limited data. Hard to say, though if you want to share all the PRs you might get more suggestions about the cause. It does seem a bit odd that zFTP would equal 15 minute power. My zFTP is within a few Watts of 30 minute power.
ZwiftPower doesn’t show that information so it’s of limited use when trying to understand zFTP/zMAP.
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5s = 777w
15s = 713w
30s = 637w
1min = 498w
3min = 397w
5min = 359w = zMAP
10min = 344w
12min = 345w
15min = 318w = zFTP (314w)
20min = 302w (had a 311 in live data that got corrupted in FIT file)
30min = 300w
40min = 275w
Everything is from March except 1min power. I’ve gone hard in plenty of races, but my 1min-5min results will be a bit better as I don’t go all out for 20+ mins.
The alternative is I’m just fitter than I think! 
Your zFTP is being calculated using a power curve. I imagine the curve might be using your 5 minute power (359 w) and 12 minute power (344w) and thinks you can go onto produce 20 minute power of around 330 or possibly 40 minute power of around 315. These might then give you your zFTP of 314.
As Paul has suggested if you want to see your zFTP lower you need to put in a higher 5 minute effort if that is possible.
However zFTP is no longer used for the race categorisation for the races you appear to be entering so I’m not sure you should be too bothered.
Raising your 5 minute power may very well increase your new ZRS of 633 anlthough after your break from Zwift you appear to have come back strongly and are performing well in your races.
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That’s odd, a 5 minute interval should not decrease zFTP as it is still mostly aerobic, a 30-180s effort I could understand
I would describe this situation as one of not having good data for your true potential at each duration. Your PRs are flat from 10-12 minutes, so 10 min is probably low. There is a big drop from 12 to 15 minutes, so 15 min is probably low. Flat from 20 to 30 minutes, so 20 minutes is probably low. The CE curve will make assumptions when you have PRs that are outliers like that. With better data it will probably make more sense.
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OK thanks, that’s useful. I think my 5min power is pretty close to my max, so maybe its just a case that I am fitter than I think, but never get an accurate 20-40min power from the races I do.
I guess the solution is to maybe to a 20-60min TFP test, but that sounds unpleasant
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Thanks Paul, that makes sense.
I try to explain how it works as best I can, but I can’t defend state secrets 
I understand how it works or should work. A 5 minute effort should not decrease zFTP, it doesn’t decrease mFTP in WKO5 either as the effort is mostly aerobic (and I can’t be bothered to go downstairs to start up my laptop for the exact % but iirc at 5min it’s 75% aerobic and 25% anaerobic)
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