Hi there,
So did the Grade last night for the first time. The average watts displayed as I cycled up sat at 283 watts, so I was excited to get a new FTP score (currently it’s 264). However, the sign at the top of the climb said I’d achieved a FTP of 254. So what’s happened there?
What happened is your time was significantly less than the 35ish to 70ish minutes that you would expect to be able to hold your FTP for.
As such, Zwift looks at the power you did for the time you took, looks at your power curve, does some maths, consults a genie, and spits out an estimated FTP for you.
It could do the same thing ((even) less accurately) by loking at your 15-second or 60-second power, and you wouldn’t expect either of those to be your FTP, right?
Your FTP per Zwift is going to roughly be 85-90% of the average power you hold up the grade. ZwiftInsider had an article with some calculations on this.
Hi.
i just finish another The Grade test.
my current FTP is 260W and i believe is accurate enough.
in the last month i was doing quite a bit of ride and tested again to see how it is.
i got an average of 247W and 17 min to finish.
First of all, i dont get why Zwift dont show the FTP even if its lower then the actual. so, its prob lower and they showed only the Average power. I looked it up in Intervals.icu and there is says that i got an estimated FTP increase of 5W resulting in 256W (there my ftp was estimated 250W). This feels about right considering my current power zones. im just a bit disapointed that there is no statistically relevant improvement ;(. im also consideriing that im a bit fatigued from the previous weeks training but wanted to check nevertheless. I might go back to test via the ramp test. It always overestimate my FTP but somehow is more consistent, idk. The intervals.icu seems to get closer so i might use the ramp test but gerht the number from the activity there…
From the Zwift Insider article :
The Grade is a 3.5km-long climb that is fairly steady (8.6% average), apart from short flat bits at the start, middle, and finish. It’s a KOM segment like other KOMs in Zwift, but The Grade is special in that it also functions as an FTP test!
How does that work? Well, Zwift looks at your average power and time up The Grade, then computes your FTP estimate based on those two figures.
For example: it’s generally accepted that your FTP is equal to 95% of your best 20-minute power. (This is how Zwift has automatically detected FTP game-wide since the early days, in fact). So if it took you exactly 20 minutes to finish The Grade, and you averaged 200W during that time, Zwift would calculate your FTP as 200W x .95 = 190W.
Sorry but I think the sections that you’ve quoted from that ZI article give a very misleading impression of how it calculares FTP on The Grade. You’ve made no mention of the all-important lookup of your power and time vs a curve based on other riders and what that means for your FTP, e.g.:
Best to read the whole article - Review: Zwift’s New “The Grade” FTP Test | Zwift Insider