Yet another FTP estimation question



bgoetz

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Nov 25, 2010
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As if there were not enough. I finally pulled the trigger on a power meter. Previously everything I had done was on the computrainer, so all my #s were based off of that. Based off of my computrainer I estimated my FTP to be around 335. Well after 2 races in the past 2 days (a prologue that took just under 20min and a hard hilly road race) the results seem to indicate I may have estimated low. My AP for yesterday's prologue was 347 in my TT position, everything I have done on the computrainer seems to indicate a drop of about 20-25watts in my aero position. Also it was not my best paced effort. My NP for today's 2.5 hr Road Race was 349watts AP 277, so VI was a bit high, but 349 for 2.5hrs!? Thoughts?
 

lanierb

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Aug 12, 2004
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If the NP349 figure is accurate your FTP is likely a bit higher than that. Probably the best thing would be to take your best 1hr NP from the race and use that. It wouldn't be uncommon for your true FTP to be higher than what you can attain on the CT.

However, that does sound pretty high, and there are basically two things that could have thrown it off: bad zero offset and bad slope. What kind of PM is it? If it's a Quarq and it's brand new the zero offset tends to slip at first (due to the chainrings slipping) which will cause the PM to read higher and higher during the ride. This will work itself out over a few weeks but during this period you need to recalibrate the zero offset often. Regardless of what kind of PM it is you need to calibrate the zero offset at the beginning of every ride and also again during the ride if there is a big temperature swing.

If it wasn't the zero offset then I think it is worth testing the slope. It takes about 10 minutes if you know what you are doing. Do a search under "stomp test" to see how it's done. There are numerous videos. The one on the Quarq site under Qalvin is pretty good and is basically the same thing you would do with a PT or SRM (except on both of those you would use the head unit instead of an iPhone). The only thing you need is a known weight of around 40-50lbs, and for that you can take a barbell to your post office and accurately weigh it. Then you have to know how to convert the units correctly.
 

RapDaddyo

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May 17, 2005
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I think I would use 350W as a first approximation of FTP, although I agree that you should follow the appropriate procedure to calibrate your PM, depending on the make and model. The thing is that if you initially plan your training rides on the assumption of FTP=350, and if that is a bad estimate, it will become quickly apparent. If 350 is overestimated, your efforts (e.g., [email protected]) will be a struggle if not impossible. If 350 is underestimated, your efforts will be too easy and it will be immediately apparent that you can handle more. So, whatever you choose as a first approximation, you will quickly figure out if it is about right.
 

bgoetz

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Nov 25, 2010
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Thanks guys! It is a powertap and I have zeroed it each time. It seems pretty accurate when I have been just messing around with it based on HR and PE. Maybe I will go from 335 to 340 and see how that works? Or am I better shooting high because then it will be more apparent when I can't complete efforts?
 

Felt_Rider

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Oct 24, 2004
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Originally Posted by bgoetz .

Thanks guys! It is a powertap and I have zeroed it each time. It seems pretty accurate when I have been just messing around with it based on HR and PE. Maybe I will go from 335 to 340 and see how that works? Or am I better shooting high because then it will be more apparent when I can't complete efforts?
I don't think I am good for the answer, but it seems like shooting high and seeing if you make it or fail is a good idea. My thinking is that we typically try to be progressive with our training anyway. So if you are pushing yourself and you don't make it at first you can then tone it down for the next training session. After a few sessions and you will probably get a feel for what you can do consistently until your FT actually (and hopefully) does bump up from training.
 

RapDaddyo

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May 17, 2005
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Originally Posted by bgoetz .

Thanks guys! It is a powertap and I have zeroed it each time. It seems pretty accurate when I have been just messing around with it based on HR and PE. Maybe I will go from 335 to 340 and see how that works? Or am I better shooting high because then it will be more apparent when I can't complete efforts?
For training purposes, you don't need to estimate your FTP with precision. If you do your L4s at 340, that is solid L4 work for an FTP all the way up to about 375W. The concept many struggle with is that you can increase your FTP without ever doing an effort above your FTP. I once went for several months without retesting my FTP. During that time I was using 300W as a FTP proxy and was doing all of my L4s at 275W. When I eventually retested it, my FTP had gone up to 326W. Remember, I had not done one single L4 effort above 275W for several months, although I had done a healthy dose of L5-L7 efforts along with a steady diet of L4s.

For racing purposes, especially TTs, it is a completely different issue. For a TT, you want to have a very precise estimate of your maximum sustainable power for the estimated duration of the ride. For a 40K ITT, that will be in the vicinity of 1hr, but you want a very precise estimate for the duration whatever that is. If you overestimate your max sustainable power, you will ride the first half too hard and will have to back off in the 2nd half, which may be the very section where you want to go harder. Likewise, if you underestimate your max sustainable power, you will ride the first half too easy and even if you ramp it up in the 2nd half you will have lost valuable time in the first half. So, prior to a target TT event, I highly recommend doing a constant power test to nail down your true max sustainable power at the estimated duration for the event.
 

lanierb

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Aug 12, 2004
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Well if your PT is reading correctly then 340 is way too low. People often are reluctant to set their FTP correctly because they know it hurts a lot to work out at their true FTP. Remember FTP is *not* attainable every day and it should be very difficult to attain in training where you are typically not maximally motivated. HTFU and set it right so you get the correct measure of CTL and so you can benchmark your workouts against it.

I'll repeat what I said above. By far the best measure that you have of your FTP is the maximal 60m NP from that race. Find that and use it. I'll bet it's in the 355-360 range. Just because you can't do it on your CT every day doesn't mean it isn't right. Also, now you know how hard 90% really is. BTW that's very impressive. How much do you weigh?
 

bgoetz

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Nov 25, 2010
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I weigh 180, and these numbers are off. Someone showed me today that there is a "non zero" setting that I needed to change. Basically I don't think it was taking times of zero power into account. So while my TT info should still be good, the RR could be off. I think I will stick with 335, I have actual data to back that up.
 

bgoetz

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I don't know? 349 NP for 2.5 hrs would be a stage of the TDF though, and we finished in a bunch sprint. I am pretty certain power is accurate, and I have it calibrated, so that just leaves the nonzero issue.
 

bgoetz

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Unless by having my AP accurate it would point out that it was an extremly hilly race, so the VI is actually far greater, so high that using NP is not accurate.
 

RapDaddyo

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May 17, 2005
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Originally Posted by bgoetz .

Unless by having my AP accurate it would point out that it was an extremly hilly race, so the VI is actually far greater, so high that using NP is not accurate.
I don't think a high VI renders NP invalid. If you look at the individual watts column in your ride file, does watts go to zero during the ride (e.g., when coasting)? Also, do you see any really unusual spikes (or "blips") in the watts column, basically a sequence that doesn't make sense such as going from 350 to 1250 and then back down to 350. If watts goes to zero occasionally and there are no unexplained "blips" then your ride file is probably valid.
 

bgoetz

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Nov 25, 2010
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Well I changed the setting on my Garmin, so I guess we will see. It said my NP was 401 for today's 60min crit, which I did before I changed the setting. The power itself seems right it is just the NP, AP, and TSS that seem off
 

lanierb

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Aug 12, 2004
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(1) If it's the Garmin the "no zeros" setting affects AP not NP so the NP values are correct assuming the PM is reading right.

(2) I'm starting to suspect your PM is reading high (slope wrong so calibrating it won't help). 401NP would likely get you the win in a Pro/1/2 race out here and this is one of the most competitive regions in the country. If you want a point of comparison, Kevin Metcalfe just today posted two power files to the wattage list from local Pro/1/2 crits and he was in the winning break in both and his NP was 325ish in one race and 360ish in the other and he is about your size and he is the masters *national* champion in the TT and the Crit and was second in the RR, so he's surely stronger than you are but according to your PM you're doing 10-20% more power than he is in a race that I'm assuming (perhaps wrongly) does not have the same quality of field. (E.g., his field had Ben Jacques-Maynes and Max Jones in it.) It raises some serious red flags. I would highly suggest doing a stomp test on your PM or taking it somewhere that can, or even sending it in to Saris.
 

bgoetz

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Nov 25, 2010
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The thing is the power seemed right on for my TT, which had no instances of non pedaling. Also the few intervals I have done seem spot on to my HR and PE. According to Garmins site that setting causes it to ignore any 0 power to calculate average power. So if AP is used to come up with NP, then NP would be off too right?
 

bgoetz

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Nov 25, 2010
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And here is the other thing with the data today, I accidentally left my Garmin on for the entire 3hr drive home, so that could have screwed things up too.
 

RapDaddyo

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May 17, 2005
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Originally Posted by bgoetz .

The thing is the power seemed right on for my TT, which had no instances of non pedaling. Also the few intervals I have done seem spot on to my HR and PE. According to Garmins site that setting causes it to ignore any 0 power to calculate average power. So if AP is used to come up with NP, then NP would be off too right?
Whatever setting your use on your PM handlebar computer is relevant only for your handlebar computer data. When you bring the ride file into WKO+, it imports the raw data and not your ride-file settings on your handlebar computer. It re-computes everything from the raw watts column. So, the only thing you need to look at in the ride file is the raw watts column. One dead giveaway is if watts never goes to zero in the ride file. This would indicate the PM was not zeroed correctly. It's almost impossible to do a ride with no time at zero watts (i.e., coasting), so you should have at least some zeros.
 

RapDaddyo

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May 17, 2005
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Originally Posted by bgoetz .

And here is the other thing with the data today, I accidentally left my Garmin on for the entire 3hr drive home, so that could have screwed things up too.
Not really, because you can easily delete that segment.
 

bgoetz

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Nov 25, 2010
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Well this may be the issue, I am using Garmin connect, not training peaks. Although connect is suppose to use training peaks formulas, so either their NP formula is jacked, or the way the zeroing functions into their NP formula screws it up. I can send someone my files if you would like to take a look on WKO
 

RapDaddyo

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May 17, 2005
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Originally Posted by bgoetz .

Well this may be the issue, I am using Garmin connect, not training peaks. Although connect is suppose to use training peaks formulas, so either their NP formula is jacked, or the way the zeroing functions into their NP formula screws it up. I can send someone my files if you would like to take a look on WKO
I don't have any experience with Garmin Connect, but I have noticed that ride files from a Garmin exclude the torque variable. But, I think you can still download WKO+ for a trial period so you can compare the ride statistics in WKO+ with Garmin Connect. Anyway, I think you will find many other reasons to get WKO+.