Estimating FTP From A Ride Like Gray (2x20 minutes @FTP)?

I did Gray in the middle of last week and am trying to see if I can guesstimate my FTP from it. I’ve been using AI FTP but I never did the 10 indoor rides so it has turned out not to be all that accurate for me. (TR bypassed the indoor ride requirement for me as I don’t have a trainer and so all of my rides are outside.)

Each 20 minute interval for Gray was supposed to be at 281, which was my FTP according to AI FTP. My first interval was 270 and the second was 248. I’m thinking that averaging those numbers (259) probably gives a pretty good guesstimate of what my FTP might actually be. Subjectively, 259 is also a number I think I could hold for 30-40 minutes. Am I off my rocker with this approach? I know I could just do a test but I don’t relish that idea…

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I’d just ride my FTP intervals at 250 (or 255). Progress time in zone. When you get to 1 × 40 start the interval at 250 (or 255) and ramp it up if you feel good. The avg power for that interval should be a great number for your FTP.

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Triangulation can work very well. Use round numbers like 250, 255, 260, 265. And what @Helvellyn said above.

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Was 270 thehardest you can go? Cause .95 of 270w is 256w. So assuming 259w ftp means your first interval was basically a ftp test. If you feel you can do 259w for a 30-40 min, id go with it

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Probably that’s pretty close. You could check on intervals.icu to see what your estimated FTP is (free) or fork over the 250 or so for wko5 (well worth the money imho) but I think both will probably come pretty close to your number

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Did @bmarum warm up have an all out burst like an FTP test? If not I’d be more conservative and say 0.92x 270 = 248 w (round it to 250w). Strong riding btw @bmarum

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FWIW a long warmup with some intervals works for me.

That said I agree and posted this earlier:

It’s likely somewhere in that range.

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If I read it correctly, you did Gray outside? If so, consider whether anything happened in either of the two intervals that would affect the result - how much freewheeling? any easing up for traffic signals or junctions? any significant up / down gradients etc.

I don’t know how you factor that in to guesstimating your FTP though.

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Thanks for all the great responses! I did the workout outside, I did have one stop sign in the first interval that I am normally able to blow through but I wasn’t this time. And it was 90+ degrees out, which is hot for the SF peninsula so something I’m not used to. So those two things certainly negatively impacted it.

I warmed up thoroughly but did not do the 5 minute blow out effort like the 20 minute ftp test calls for, so that made me fresher than I otherwise would be. 270 for the first interval was an all out effort and intervals.icu pegs my ftp at 256.

When I first set my ftp back in January, I did the 8 minute test built into my Wahoo. And up until very recently, TR has been giving me a lot of shorter intervals. I suspect I am better at 8-12 minute efforts and worse at longer 20+ minute efforts. Given my lifting and rowing background, this doesn’t surprise me. And if that’s right, the 8 minute test probably overestimated my ftp. I likely need to spend more time on longer efforts as @Helvellyn suggests.

Go read about the intent of that on the original test (it was to estimate power at vo2max, and shake off some freshness). Plenty of coaches that do NOT do a 5 minute all-out effort. I’ve done my 20-minute efforts at the end of week 3, before a rest week, and I wasn’t fresh. Plus I could show steadily increasing HR and breathing while doing intervals just 10-20W above my estimated ftp. That is really what you are looking for, a small range of power where breathing/HR are steady state, and going just a bit (depends on person, for me its 10-20W) above results in relatively steady increase in breathing and HR until hitting max aerobic breathing and max HR.

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I did not know that about the 5 minute effort. My heart rate during both of my 20 minute efforts was relatively stable even towards the end of the intervals. But I did not feel like I could have continued either interval much past the 20 minutes. I was going to say that it was also essentially at my LTHR, but now that I think about that when I tested to set the LTHR I did it using two 10 minute intervals if I remember correctly which is now making me wonder if it too is higher than it should be.

There’s a local climb that I’ve wanted to take a run at setting a pr on for a few weeks now. My best time is a little over 30 minutes, so perhaps my answer is just to do that this coming week and then look at both my heart rate and power data.

So I went and did the local climb today. Set a solid pr – finished in just over 28 minutes. It was close to an all out effort, but had I needed to climb for another 5-10 minutes at roughly the same pace, I likely could have.

Guess what intervals.icu thinks my FTP is? 281. Exactly what AI FTP thought it was despite me not having done a single indoor ride. Perhaps the 90+ degree heat on the day I tried Gray did me in more than I thought it did. Or maybe the awesome burrito I had for lunch was a performance enhancer. Who knows. Anyways, here’s what the ride looked like:

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