I suppose I’m asking more from a place of intellectual curiosity, but within the last 10 days or so, my zFTP dropped quite a bit and I was downgraded to B (women’s) after I’ve been racing A consistently and successfully enough. Just curious if there’s any idea what’s going on here.
Current zFTP calculation is 244W. My 20 minute peak power in the middle of a race just this last Tuesday (so not a true AO effort) was 271W (I know it’s not using 95% of 20 min, but just for reference 95% of that would be 257) and I have non-max efforts in the last 45 days that exceed my zFTP up to 51 minutes.
Just seems very odd. Zwift itself has me at 257, intervals.icu says 276 (too high I think). Why is CE calculating me so low? I won’t race in women’s B races but just curious.
zFTP is a prediction of what you can do for 40mins.
Given you actually did 252W for 40mins on 7th March (i.e. within the last 60 days) just on Zwiftpower, which won’t show your activities that aren’t races; workouts or group rides…
It’s curious why your zFTP is 244W.
Is there a minimum zFTP of 250W to be in women’s A pen, just like for the men?
James confirmed in the Category Update thread that changes to zFTP were made last week.
The outcome is that many have seen a reduced zFTP, and for some (like me too), that means a lower category. Effectively the category boundaries are now higher than before, because it will take more power to get to that zFTP level again.
Yeah, I get that, I guess I’m just wondering what about my curve would be pulling the zFTP so low. I see some people talking about a big delta between 5 min w/kg and 12 min w/kg pulling the curve steeper and lowering the zFTP, but I don’t think I have a particularly strong 1 min, 5 min, 12 minute in comparison to my 20 minute.
Suppose it’s not really all that important in the real world, and plenty of others are seeing similar, but as a low-level data nerd I’m just curious how this could work.
I’ve had the same happen to me. I’d been a low A under the 20-min power system (FTP ~4.25w/kg) but my zFTP has dropped from 314W to 296W - until I came down with a cold a fortnight ago, my power had been gradually improving in all but the shortest sprints, so I can’t really imagine that my critical performances were dropping out of the back of the 60-day window…
At the very least the new CE comms have been non existent. People suddenly dropping lots of places in races will have no idea why unless they are diving into the depths of these forums. And even then you need a PHD to understand it. At first I thought I had inexplicably dropped fitness.
Sorry for necro’ing this thread, but wasn’t sure where to put this. I noticed something odd with my zFTP this week, and wonder if anyone else noticed a change as well. It seems to be lower than it should given my last 90-day efforts.
So, I did do a ‘refresh profile’ on ZP, and it matches what is shown on zwift.com, that is a 266 zFTP - which I know is “not FTP” but ‘should’ be an estimate for what I can sustain for 40mins+. But… I have multiple efforts above that power at 40 mins in length, and intervals.icu’s eFTP put my last race at an eFTP of 289W. My last ramp test a week ago put me at 306W for FTP, but I know ramp tests tend to overestimate my FTP, so I’ll ignore that for now.
Here are my stats showing a much stronger 30 min and 40min than my zFTP would indicate:
Any theories as to why the zFTP is showing well below my 30min power, and even well below my 40min power? I do have a close to max effort 5 mins (recent ramp test is almost like a max 5 min effort), and a reasonably strong effort at 30mins from my last race in there. So I definitely have pretty solid efforts (for me) in the 5-30min range).
Maybe related, but my VO2Max seems much higher than it should be too. Wondering if something is messed up in their calculations.
I haven’t done a full-out 1-hour effort in the last 90 days, but checking intervals.icu a tour de wattopia ride on Nov 6th was 264W for an hour which is almost identical to what Zwift has for my zFTP.
I have a similar issue my zFTP has dropped from 276 to 268 in recent days and not really clear why based on the 90 day numbers? I did a race earlier and intervals.icu suggested eFTP of 282?
I believe that higher short term power can drive down calculated longer term (ie. zFTP) power. Are your shorter timeframe power numbers (5-15 minute) newer and higher than they were before the zFTP change, while your longer 20 - 40minute numbers being used are the same as they were?
Yeah, I’ve been playing a bit with online FTP calculators to see how different efforts affect some versions of curve fitting - though I don’t exactly know the algorithm Zwift uses, but I do find there’s a pretty big difference in output if the 5min range shifts while keeping the longer ranges steady in at least one of those online calculators (I think the curve assumes max efforts for both). So, if you have a particularly strong shorter (5min-ish) power recently that could be the difference and force down your zFTP - in which case you’ll then need to get a max effort in the 12min+ range to get back to an accurate FTP.
