As I go through the Zwift forum posts, the difference between Zwift FTP and Zwiftpower FTP seems as confusing now as it did 3-4 years ago! Hey Zwift, surely you could choose to rectify this? As with any well engineered app, shouldn’t only ONE master record rule supreme? Or couldn’t you publish clearly how the number is calculated?
Case in point, my Z FTP was sitting at 299 and my ZP FTP at 304 two days ago. I did my first TT yesterday, setting a new 20 minute power high of 325. At the end of the race, it congratulates me for ‘detecting’ an increase in my FTP from 299 to 313’. (And it asks me ‘if I want to accept’ my new number…are you kidding me, it’s asking me what my score should be?!). Then I check the race results in ZP…and it has DROPPED my FTP from 304 to 296!?
This is just utterly confusing. I’m guessing Zwift could fix this if they wanted to? Either use a single source of truth - or clearly explain to the loyal Zwift users how the numbers are calculated. (Can you imagine a basketball game that provided two different scores at the end of the game…so who won??)
Perhaps Zwift takes the position that any news is good news? Let the loyal, paying users bicker over these calculations because it creates activity in the forum!?
The zFTP shown in Zwift power (which is just a feed from your zFTP in Zwift) is completely different* to your FTP in Zwift. Yes, it’s silly. Yes, Zwift were told to call zFTP something else. No, they didn’t listen.
The former is a modelled number based on your best power at a couple of durations over the last 90 days.
The latter is whatever your FTP is set at in Zwift. Could be from an FTP test. Could be from a single 20 minute effort. Could be from setting a PR on The Grade. Could be manually entered.
*not completely, obviously. Both are meant to (sorta) represent the power you can maintain steadily(ish) for 35(ish) to 75(ish) minutes, but they take different inputs to do that, and as a result we should expect different outputs.
ETA: This is also why it’s reasonable for Zwift to ask you if you want to accept a change in detected FTP - you may not want your power targets for future workouts to be recalculated just yet.
was your TT significantly over 20 minutes? 95% of 20m power of 325w would only be an FTP of 309 watts, but maybe Zwift has another means of establishing FTP in game other than 95% of 20m)?
As an add-on to what David also said, consider your zFTP as being a Category Enforcement FTP – what the game would use if we still had CE races. Your other FTP can be manually set, so of course that would have been unusable for determining eligible race categories.
Thxs for the explanation David, sounds like both measures will continue to confuse[quote=“David, post:2, topic:643062, full:true, username:David_Galbraith”]
The zFTP shown in Zwift power (which is just a feed from your zFTP in Zwift) is completely different* to your FTP in Zwift. Yes, it’s silly. Yes, Zwift were told to call zFTP something else. No, they didn’t listen.
The former is a modelled number based on your best power at a couple of durations over the last 90 days.
The latter is whatever your FTP is set at in Zwift. Could be from an FTP test. Could be from a single 20 minute effort. Could be from setting a PR on The Grade. Could be manually entered.
*not completely, obviously. Both are meant to (sorta) represent the power you can maintain steadily(ish) for 35(ish) to 75(ish) minutes, but they take different inputs to do that, and as a result we should expect different outputs.
[/quote]
Just to add to your confusion, zwift is quite special and you have 3 sets of results for a race…
Take a standard points race:
You have the zwift.com results (which might impact ZRS,kinda 50/50 currently if they do or don’t) but don’t reflect the points aspect of the race so are by the rules of the race inaccurate.
You have zwiftpower results, which reflect the points aspect but don’t have all of the racers as zwiftpower is still optional.
Then, somewhere out in the ether will be the results ordered by points that includes all riders who were in the race.
For all the changes zwift have implemented, you would think accurate results would have been the starting point.
With regard to ftp,
ZFTP = CP (modelled 90 day power)
FTP = 95% of 20min power
So, the other factor is that there are many riders who train on and use other platforms. Some people import workouts from other platforms as well. Many of these are based on zones and specific percentages of “FTP”. For obvious reasons, some people want to have some control over their FTP metric so that there isn’t a disconnect between software and training platforms.
Your FTP sets your training zones in Zwift, and hence your power targets in workouts. There are plenty of legit reasons why you don’t want your training for January and February to be benchmarked from a single 20 minute effort you had while super-fresh in December.
So basically what I take from all this - and thank you all for your input - is to use Zwift FTP for training purposes and to rely on ZP FTP for your true FTP score?
(Although, I still have to add that setting a PB for 20 minute power and seeing my ZP FTP drop by 8 watts is a bit confusing. )
With regular power based Category Enforcement gone now, and replaced by RacingScore, you can pretty much just ignore your zFTP shown in Zwiftpower or in your myZwift profile. The caveat to this is that your FTP can decline (age, illness, laziness, etc). Continuing to use an FTP value based on potentially a really old 20m power record would be wrong, and your zFTP could directionally be telling you that you need to change your regular FTP and in fact be more accurate than using an expired and outdated other FTP – ie. in which case it’s time to take a new structured FTP test.
Sorry to keep this post going David, but if FTP is not a score, then why has Zwift been treating it like a score? W/KG - which appears to be based on FTP - seems to be the ‘score’ Zwift has been using to control races? With the new Zwift Racing Score now appearing, does this now mean that W/KG (and by extension FTP) is a secondary measure simply for training purposes?
FTP is a half-decent predictor of endurance race outcomes. As such, it was (while not without problems) a broadly sensible way of splitting racers by ability.
The problem was always that fixed boundaries btwn categories create artificial ceilings and floors that encourage people who like doing well in races to only get so fit and no more, by fair means or foul.
I’ve completely disassociated FTP, zFTP and ZRS in what passes for my mind.
FTP is “what I base my Sweetspot and Threshold intervals on”
ZRS is “what determines what category I enter for races if I ever get round to doing any”
zFTP is “what gets spat out by the Zwift model when my ‘best efforts’ over the last 90 days are fed into it”
Current FTP: 245w. Current zFTP: 217w. Can you tell I’ve not being doing anything harder than a few 3 × 10 minutes at FTP since September? I have added quite a bit to my squat, deadlift and bench, though.
I have added quite a bit to my squat, deadlift and bench, though. 
