FTP vs ZFTP

General Discussion
1

So Im a new-ish Zwifter (August). In October I got a notice that my FTP increased to 213 and bumped me up to Cat C. Three weeks ago I began the FTP Builder workout with a ramp test. Results from the ramp test indicated my FTP to be 243. However, my Zwift profile and Companion app still show me having a zFTP of 213. Is this normal?

2

It can happen since the ramp test is short in duration and you only hold any given power level for about 1 minute. Do one of the 60 minute+ non-ramped FTP tests instead, or go all out in one of the Zwift TdZ races this weekend.

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3

I struggle with some of the tests to give my full effort as it feels a bit artificial. I typically use results that I have gotten from races. I push myself to the limit while racing where I am literally gasping. I use the ftp results from those efforts to set my training zones.

I think that it is important to recognize that all of these things are estimates designed to help us determine where different energy systems are being primarily used. That is why each zone has a range. And there is always overlap.

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4

Ramp test are not very accurate, so I am not sure if zwift uses them as your FTP

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5

First things first: Your FTP and your zFTP are pretty much completely separate, so the fact that they do or don’t match is a non-issue. Don’t give it a second thought. If they do match, it’s a coincidence.

Your FTP is used to set zones for workouts. Your zFTP is used along with zMAP to decide which category you’re going to race in.

On the subject of your FTP test results - ramp tests work OK for about two thirds of people in the middle of the bell curve. If you’re very anaerobic or very non-anaerobic then a ramp test is likely to overestimate or underestimate your FTP respectively.

If you want a quick validation of your FTP number, load up a workout with something like 2 × 15 minutes or 3 × 10 minutes at 100% of FTP and see how it feels. If you can complete it at a rate of perceived exertion (RPE) of 8 out of 10 - maybe a 9 by the last couple of minutes of the final interval - your number is probably good.

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6

There are actually 3 versions of FTP in the game right now.

  1. Auto-detected FTP that shows the “Your FTP has increased” banner: This shows when you’ve got a personal best 20 mins in Zwift, and the value is 95% of that 20min value.
  2. zFTP: This is a calculation based on multiple points on your power curve, using a shorter max effort (Such as 5mins) and a longer effort (such as 12mins+). You do not need a max 20min effort for this. This does NOT affect the FTP used in workouts as far as I know.
  3. FTP tests: After you complete a ramp test the value of your FTP in settings used to calculate your workout zones is changed if that value increased as part of the test.

So, if your only max effort was a ramp test that might be your best number. It is unlikely the one Zwift auto-detects will be correct, and the zFTP number will only be correct if you’ve done a shorter AND longer max effort.

So, I would try doing a threshold workout at the FTP set via your ramp test to see how it feels as David mentions. If you are new to structured workouts a 2x15min threshold workout might be too much to start with, you can try a 3x10min if 15mins is too daunting as another idea. If you can’t get through a 3x10min at threshold then it would be worth bumping it down a bit, but if you can, then my guess is you probably will be ok.

What I did was took a ramp test, then used that value to help me pace the 20min test. But the 20min test is a pain.

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7

… and if you want to find your FTP rather than testing and multiplying by an arbitrary %age to get an approximation of it, have a read of this:

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8

Thanks everyone for your comments. I am liking this community so far! Being an older fella and just entering cycling as a dedicated hobby all this information will be really helpful. As I alluded to in the original post, I am finishing up week 3 of 6 of the FTP Builder workout. Wondering if i will get a more accurate zFTP and FTP afterwards or during…

9

Well, you won’t get an accurate auto-FTP detected as part of the workout plan because none of the workouts are focused on a single max effort (except the ramp test), so nothing within the context of those workouts ‘should’ increase the auto-detected FTP if your FTP is set correctly.

That said, if you take a ramp test during or after the program you might see an improvement, and if you do a 5min AND 12min+ max effort after the program you could see a zFTP improvement.