Instead of these numbers post a screenshot of the page which has the power numbers for various times.
It’s a curve fit so shouldn’t be hard to state why this number is given to you.
The curve I understand but my issue is my value for zFTP is a number vastly in excess of what Intervals.icu gives for their estimation of my FTP at 271 (based on a 20 minute effort) this is why i was asking if is it is picked from a point on the curve and extrapolated as by default intervals uses 3min which can result in some extremely off and high FTP numbers
nothing seems to have dropped off, 30s and 30min will drop off soon but that shouldn’t affect zFTP surely?
-
5 sec771 w10.45 w/kg
-
19/01/2023, 19:27:09
-
30 sec534 w7.21 w/kg
-
24/11/2022, 20:01:30
-
1 min490 w6.61 w/kg
-
13/12/2022, 20:43:32
-
3 min402 w5.43 w/kg
-
30/11/2022, 20:06:28
-
5 min356 w4.8 w/kg
-
13/12/2022, 20:43:32
-
12 min324 w4.39 w/kg
-
20/01/2023, 18:32:21
-
20 min285 w3.85 w/kg
-
11/12/2022, 18:21:19
-
30 min276 w3.72 w/kg
-
24/11/2022, 20:04:07
a lower 30min might have an effect. i do think they measure long efforts, contrary to what i previously thought which is that they took your 3 and your 12 min, guessed everything from that and then called it a day. fair play to them, it’s clearly more sophisticated than that
Still can’t see how that equates zFTP to 299 from my numberw though, still it’s Zwift I doubt I’ll get a response on it
Raise you 20min, 30min and your zFTP will go down…the range in W from 12min to 20min is to big 
zFTP is showing as 297 now
I seem to have had the same issue. I put in a big effort on and uphill section during stage 4 of Tour De Zwift. My 12 minute best has increased to 276w, which has led to my ftp increasing to 262. However my best 20 minute effort is 245w. This has now put me up to Cat A on Zwift (although not ZwiftPower). What I find strange is that people much better than me are still Cat B. It’s nice to have got into Cat A, but I know I’m going to get spat out the back in most races.
During a race or did you do a puke in a bucket and fall of the bike FTP test to get this number?
1 Like
That TDZ stage 5 short race (Gotham Grind) is pretty much designed to give you a max 12 minute power 
It also boosted my zFTP, it’s rare that I see boosts in events because I have done many FTP tests and most races require some recovery between efforts, but Gotham Grind in particular is one that will probably get a lot of folks who are treating it like a race upgraded.
Edit: Oh I see it was stage 4 that gave Paul his best 12 mins.
so can you provide the formula zwift are using for estimation of zFTP then?
No .
I was asking how certain he is that 245 is his best 20 min power.
Looking back at his Strava you will see higher 20power in the order of 260 w.
There is very few races that require you doing a true 20 effort.
But why is Zwift calculating a higher number ?its obviously basing it off a lower than 20 minute effort
My zFTP is supposed to be 297 yet my 20 minute is 285 from a ZRL race …my zFTP only went up after a 12 minutes effort up Keith Hill so explain to me how it’s calculated the difference as previously I was showing zFTP as 263
Nice to see Zwift being nice and transparent as usual
I suggest to look at your power profile in apps like intervals.icu.
I had a very recent experience with a gap that the CE simulation/calculation has when the power curve is slight upward (my case was around 10-12 minutes). Then it can model that you can do more watts for 40 minutes (zFTP) than you do for 20 or less.
Another thing to try is to do some harder shorter efforts like 2-5 minutes (which Zwift suggested multiple times here btw.) or do a race on Insbruckring like today’s ZRL which ensures the same 
. The thought is that the curve will be steeper and mitigate the gap I wrote about above.
Zwift is calculating a higher number because he can probably do that higher number. He did it in September.
I do a fair amount of 10 mile TTs both in real life and on Zwift and have noticed that my ave has dropped from 250w a couple of years ago to 240ish in the last year (I hit 60 last year, so would expect a gradual decline). It’s always felt like I’ve given my all, but I’ve never thrown up, so maybe I’m just not trying hard enough 
2 Likes
And to be clear I’m not complaining, I’m delighted to say I’ve reached Cat A at the grand old age of 60.
I did have a higher ftp in Zwift a few years back, but that was with a wheel on trainer, which I knew was skewing my online figures (and was quite frankly embarrassing). I was just surprised when I went to sign up for the “Flat is fast” race this evening and couldn’t do my usual Cat B. As it was I managed to stay with the leading group, although was trounced in the sprint, so maybe Zwift is correct. I’ll just have to see how I do on a longer hillier course.
3 Likes
I know you were not complaining. I was replying to Rick.
Congratulations on reaching A category, my aim is to reach A this year.
We don’t typically do 20FTP testing just for fun. 
1 Like
Well now! If you’re with the leaders in an A race, that sounds like you’re an A. Not every route will favor a given rider. If you want to win you may need to be selective about where you race. A good goal would be getting to the top of the 60+ riders in A.
1 Like
The same has just happened to me on the stage 5 race.
I track my eFTP on Intervals and it has been with 2 points of my zFTP.
Today, I improved my 12 min power.
Intervals set my new eFTP to 214 but Zwift increased it to 229.
Has the formula changed?
I’m on about my personal zFTP, it went from 263 to 299 after 12 minutes effort, your own blurb states zFTP is power over 40 minutes or so
Explain to me me how my zFTP went up 30odd watts from a 12min effort because if Zwift is calculating it from short efforts and making an assumption of what I can hold then it has its calculations all wrong
even if he did it in September how is that relevant to the 60 days of CE calculations that Zwift use?