Just wondering if someone could advise what has caused me to very quickly move from C to B? Doesn’t seem to make sense from the below summaries - the first is mine being Cat B, the second is a friend (who produces a lot more power) who is only Cat C.
Thanks.
Mike
That does seem a bit odd. I can’t spot the reason for the difference but just adding another data point from a rider nearer to your power and weight than the other guy.
I wonder if this is one of the cases where doing a harder short effort (3min) would actually pull down the calculation.
It can’t hurt to try. Worst case you just stay where you are.
That’s me at 86.8Kg, so zFTP is under 3.05W/Kg (threshold is 3.36W/Kg), zMAP is ~3.6W/Kg (threshold is 4.2).
Mike’s 5min+ W/Kg are higher than mine and the drop-off is less, especially 5min to 12min.
My pin the tail on the donkey hunch is Mike needs to find more 5-8min ish horses. 
Welcome to the forum.
I would guess it is the cliff at 17 minutes. The formula would predict something like the pink line (line is just for illustration)
As others have suggested i would try do some very hard efforts at 1-3 min range might pull you back down.
I doubt that will work, that 17min is way to high.
More to the point; what’s going on with that curve beyond 17 mins.
Looks very flaky?
17 minute PR set in a short hill climb race and nothing else similar, but longer, to compare it to. In other words the values immediately beyond 17 minutes are not accurate reflections of capabilities, so 20 minute power will be guesstimated by CE as higher.
Isn’t it unusual for zFTP to be higher than 30min power? I’d agree with idea to go do a little warmup and then crush a 5-8 minute effort.
fwiw, evidently any effort less than 5 minutes has no impact on zFTP
Ah yeah, I forgot if it was 3 or 5 mins as the lower bound for the curve calc.
Thank you - at least it’s not me completely mis-understanding things.
Exactly as has been suggested, I put in a really hard effort over a short race - which has created these figures. Over longer distances I can’t sustain this power.
Does the short (5-8min) effort need to be over a defined segment? Ie KOM, Sprint etc, or can it be at any time? I’ll give it a try. 
Thanks again.
Mike.
Out of interest, how do I get to see that curve?
Category Enforcement will use the power you produce at any point in any of your rides on Zwift, so you don’t need to do a KOM etc. That said, if your 17min power is high enough you might still come out of it with a B cat rating.
Yeah, that is a cliff there. Though, even that 17min effort I think is (coincidentally?) equal to his calculated zFTP.
It was a lot easier to answer these questions when we had a scoobies how it was calculated. Now the answer is: suck it up.
Apologies if you’ve seen this before - first time for me.
