Yet another FTP estimation question
- Thread starter bgoetz
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I have noticed that PT PMs occasionally capture bad data. Actually, I have encountered three types of bad data: (1) blank watts, (2) duration error and (3) watts "blip" which is an unusual jump for one or two observations in watts in an otherwise steady power segment of the ride file. I have had to build algorithms in my ride file parsing application for this problem. Each post-ride analysis application will deal with these "bad data" differently, which can account for differences in their computed statistics. In my application, I exclude the bad data observations completely, but other applications may deal with them differently. FWIW, I have never seen a single bad data observation in an SRM ride file. I have an algorithm to deal with it if I ever encounter it, but it has never been invoked.
OK now I think I figured out what's going on. I'll bet that you have "Smart Recording" set to "On" on your Garmin. If that's the case the NP figures will be inflated/false even if the power meter is reading correctly. Set it to record every second instead.
I was about to post that same thing. Smart recording is the dumbest thing out there. It will screw with the numbers, both real time and post-hoc calculations no matter the software used.
You should be able to tell by looking at the time column in the raw data mode of WKO+. Is there a data point every second? Does the watts column vary (even slightly) each second or do you have multiple (non-zero) data points with watts equal? Whatever your settings, that is the raw data imported from your ride file. Even when I am riding at a very steady pace, the watts column in a ride file is rarely equal for two or more observations. I don't know what it looks like if you have smart recording on, but it should either not have a data point every second or the watts column should be constant for several observations.
I have read others say that the Edge will automatically switch to 1s recording, but I am not sure when that supposedly switched over. As of last year one would have to manually change settings for use with a power meter. I have been using the Edge units for a few years and adjusted the settings manually (except I let the computer calculate wheel circumference instead of doing a rollout and manual entry). Probably I should do the wheel rollout measurement as well I guess.
I may be wrong about this on the "smart recording", but my understanding that it was created to save memory storage on the device. This was created for those who do not use power and monitor basic metrics like average speed, speed, mileage and so on. I think it records when there is a change in speed, cadence or other variable. I suppose on a hilly route it would pick up a lot more data compared to a flat road with a constant speed. If that is the case and your TT was flat and/or you used a fairly constant power output than it seems like your TT data would be okay. If your TT was on variable terrain with a non constant torque than your data may not be as accurate.
Others, please correct my thoughts if this is not true.
Bottom line is that these things will be past history and you will have plenty more races and training to add. The best thing about WKO+ is having weeks / months worth of data and start looking at the PMC to see how different efforts impact recovery and other issues. It has been very helpful to me as a newbie to get an understanding of training, adaptation and recovery.
I may be wrong about this on the "smart recording", but my understanding that it was created to save memory storage on the device. This was created for those who do not use power and monitor basic metrics like average speed, speed, mileage and so on. I think it records when there is a change in speed, cadence or other variable. I suppose on a hilly route it would pick up a lot more data compared to a flat road with a constant speed. If that is the case and your TT was flat and/or you used a fairly constant power output than it seems like your TT data would be okay. If your TT was on variable terrain with a non constant torque than your data may not be as accurate.
Others, please correct my thoughts if this is not true.
Bottom line is that these things will be past history and you will have plenty more races and training to add. The best thing about WKO+ is having weeks / months worth of data and start looking at the PMC to see how different efforts impact recovery and other issues. It has been very helpful to me as a newbie to get an understanding of training, adaptation and recovery.
Yes, the smart recording feature is for the purpose of saving storage on the handlebar computer, because it was once much more limited than today's devices. But, I think the algorithm is focused primarily on the GPS tracking file, so a segment with a constant heading and elevation would be recorded by recording the beginning and end of the segment since the tracking file is a straight line between the two points. I may be wrong, but I think that even if your speed varies between two points on a flat, straight road segment it will record only two points, the beginning and end of the segment.
That sounds more like what I remember compared to what I posted. My memory ain't like it used to be. /img/vbsmilies/smilies/smile.gif
It makes sense if you look at smart recording from the perspective of its original purpose, to record a condensed GPS tracking file. I imagine a 3-dimensional geometry guy won the debate when they were discussing smart recording. After all, he would argue, who needs interim points to draw a straight line between two points?
It made sense when they originally thought it up, when using it allowed you to record 4 hrs of GPS info instead of 30 minutes and there wasn't anything else like power or speed or heart rate. In the Garmin 500 which can record like a year's worth of activity even at 1 second intervals, smart recording shouldn't even be an option let alone the default.
Ok, here is what I have figured out. I think when the Garmin detects a PM it switches to record every second, when I put the data into training peaks there is a data point every second. Also Training Peaks seems to maybe be independent of the average zero setting because it seemed to include zeros in the data and my NP and AP were different then what Connect had. However, my #s NP still seems somewhat high, it indicated 312watts for the entire 2.5hr race and a max 60min NP of 338 watts. My AP in training peaks is MUCH lower with 193watts for the entire 2.5hrs. Keep in mind, I was totally cooked at the end of this race with full leg cramps, so it was all I had.
For the 60 minute criterium that I did yesterday my NP was 361watts and my AP was 282watts. It was a really intense race in which I did quite a bit of work and had a shot at taking it in the bunch sprint, but someone closed the door on me and I took 4th. Again this is MUCH lower than what connect shows my NP and AP
So with this, plus the fact that the numbers I am seeing when I am actually completing the efforts seem reasonable, is it somewhat safe to assume my PT is reading accurately?
Also assuming these are correct numbers is 335 FTP maybe to low? These are difficult Cat 3 races, in which I play a very aggressive/dominant role.
For the 60 minute criterium that I did yesterday my NP was 361watts and my AP was 282watts. It was a really intense race in which I did quite a bit of work and had a shot at taking it in the bunch sprint, but someone closed the door on me and I took 4th. Again this is MUCH lower than what connect shows my NP and AP
So with this, plus the fact that the numbers I am seeing when I am actually completing the efforts seem reasonable, is it somewhat safe to assume my PT is reading accurately?
Also assuming these are correct numbers is 335 FTP maybe to low? These are difficult Cat 3 races, in which I play a very aggressive/dominant role.
If you have zeros in the watts raw data column in WKO+, it is very unlikely that your PT is overstating watts. If your PT hub has not been zeroed, it can be overstating or understating watts. If it is overstating watts, then your watts column will never go to zero, even when you are freewheeling. That's why it is a dead giveaway that you need to zero your hub if you examine a ride file and watts never goes to zero. This will overstate watts for the entire ride and all your data will be skewed. The reverse is true in that it can be understating watts, but you can't tell this from the ride file because watts is zero or positive only. So, if your watts raw data column goes to zero, your hub may be understating watts but it is not overstating watts. I hope that makes sense. So, if your watts raw data column has zeros, I think your AP and NP statistics in WKO+ are reliable. I don't use Garmin Connect, so I have no opinion on their algorithms.
Well 361NP still seems a bit high to me but at least it's *possible*. The 401 was simply not believable unless you lapped the field and even then not really. Still, that kind of power ought to get you better than 4th in a Cat 3 race! You could have just solo'ed off the front at 350w and held it for an hour all the way to the finish and there's no way they catch you, or you could have just held 380 for the last 20 minutes and there's no way they catch you,... the possibilities are many. That's some serious wattage! It's comparable to the best riders I know and I live near a lot of superstar riders -- ex Olympians, national champs, ex Tour riders, etc. Not saying it's for sure wrong, but it makes me at least a bit skeptical, *especially* because it comes from a Powertap so is downstream of the transmission losses. When comparing to the pros, most of whom use SRMs and Quarqs, you need to add about 10 watts, so you're at 370NP for an hour. That's a lot.
Anyway, here are some things to think about:
(1) Turn Smart Recording off. You don't need it and it can screw things up.
(2) TrainingPeaks is in fact independent of the zero average setting on the Garmin. The zero average setting does not affect the way the data is recorded, just the Garmin display.
(3) RapDaddyo is incorrect in saying that if the watts column goes to zero then the PT is reading correctly. If the watts column goes to zero then the zero offset is set correctly but the slope could easily still be off (and this is reasonably common).
(4) If the PM is reading correctly I think your FTP is likely around 350 or even a little higher on your road bike. Some might say 360 but then there's sort of a 5% margin for a very stochastic road race so 350 seems about right. It would be reasonably common for you to not be able to quite achieve this on the TT bike.
If it were my PM I would probably stomp test it at this point. It takes only about 10 mins. If I had to guess I'd bet it's reading maybe 5% high. If you don't want to do a stomp test you could either send it in, or weigh yourself and the bike right before leaving and then time yourself climbing a big hill (the bigger and steeper the better). If you send me the file I can tell you if it's reading correctly.
Anyway, here are some things to think about:
(1) Turn Smart Recording off. You don't need it and it can screw things up.
(2) TrainingPeaks is in fact independent of the zero average setting on the Garmin. The zero average setting does not affect the way the data is recorded, just the Garmin display.
(3) RapDaddyo is incorrect in saying that if the watts column goes to zero then the PT is reading correctly. If the watts column goes to zero then the zero offset is set correctly but the slope could easily still be off (and this is reasonably common).
(4) If the PM is reading correctly I think your FTP is likely around 350 or even a little higher on your road bike. Some might say 360 but then there's sort of a 5% margin for a very stochastic road race so 350 seems about right. It would be reasonably common for you to not be able to quite achieve this on the TT bike.
If it were my PM I would probably stomp test it at this point. It takes only about 10 mins. If I had to guess I'd bet it's reading maybe 5% high. If you don't want to do a stomp test you could either send it in, or weigh yourself and the bike right before leaving and then time yourself climbing a big hill (the bigger and steeper the better). If you send me the file I can tell you if it's reading correctly.
1. Validate power meter calibration
2. make sure you do a manual torque zero before every ride (don't rely on auto zero)
3. Disable smart recording
4. I would tend to believe WKO+ numbers for NP/TSS over something else.
Where are you located? I provide a power meter calibration service here in Sydney if needed.
What if I put my bike on the computrainer and compared the numbers? Would that be a good way to check the calibration? Also how do I do a manual torque calibration vs the auto calibrate? Also, my AP now seems reasonable (196 for RR and 283 for crit), just the NP is high (316 RR and 361crit). So you still thinking calibration issue? I suppose the data could still be suspect, I do use the "auto pause" feature could this also be screwing things up?
Spend a little time carefully stomp testing it. Test using a couple of gears and make sure that the gear ratios you believe that you're using actually are what you're using, that the cranks are at 90 degrees to the weight being applied and if you're using your body weight for the test, that you weigh yourself just prior to the test (this assumes your scales are accurate) and that you put all your weight on the pedals - I put my bike on the trainer to aid with stability. If the torque reading calculated matches that shown then life is good. Go ride and enjoy, Remembering to zero the head unit isn't critical unless the temperature has changed a fair amount. On long, all day rides I'll re-zero midway through the ride. If it gets warm enough to warrant removing bike clothing then it's warm enough to warrant zeroing again... IMHO.
