FTP after calibration?

beldon said:

Ok then. I got my srms 12 months ago and thought my FTP was approx 300 watts when racing.

I then bought a powertap and lo and behold, the srm`s dont seem right. They get calibrated and are out by some margin.....

All previous data in the bin!! Thank you very much.

Why not just go back and correct the slope used to calculate power for these old files? Yes, it's a bit tedious, but it's better than throwing away a year's worth of data. (Note that you can change the properties of an SRM file from within their software w/o actually opening it...IIRC you just right-click on that file when in the equivalent of WKO+'s Calendar view, and up pops a menu that allows you to edit it.)

beldon said:

I have completed a MAP test this week and got to 435 averaged over the last minute. Armed with this new information, coach has given me some intervals to compete today as follows...

5 x 3 mins 30 at 360-370 watts with 3 mins rest between,

8 mins rest and repeat above.

I basically twiddled between at around 100 watts ish. The 60 mins NP is showing at 304 watts. Without completing a full 60 min test can i draw any conclusions from this? What can I expect FTP to be now?

Based on the normalized power, I'd conclude that your functional threshold power is probably at least ~290 W ("at least" because this may not have been a maximal effort and because I would consider the normalized power algorithm to be accurate only to w/in +/-5% at ~1 h). That's a bit lower than the 313-335 W that, e.g., Ric Stern would estimate based on your MAP test results, but in the same range (esp. considering that I'm being conservative).

acoggan said:

Why not just go back and correct the slope used to calculate power for these old files? Yes, it's a bit tedious, but it's better than throwing away a year's worth of data. (Note that you can change the properties of an SRM file from within their software w/o actually opening it...IIRC you just right-click on that file when in the equivalent of WKO+'s Calendar view, and up pops a menu that allows you to edit it.)

Based on the normalized power, I'd conclude that your functional threshold power is probably at least ~290 W ("at least" because this may not have been a maximal effort and because I would consider the normalized power algorithm to be accurate only to w/in +/-5% at ~1 h). That's a bit lower than the 313-335 W that, e.g., Ric Stern would estimate based on your MAP test results, but in the same range (esp. considering that I'm being conservative).

I`ll try the change with cyclingpeaks. Only issue with that is how do you know when the slope was out? Its abit guess work doing that I would think but better than losing the data as you rightly say.

I think i could go harder. This was done on the turbo and I dont usually see as high a figure as i would in say a 25 mile TT.

Thanks for the info in anycase

beldon said:

is how do you know when the slope was out?

If you're the original owner, I'd say you have two options:

1) assume a linear change from when you got it to when you recalibrated it, or

2) assume that the new slope is what should have been used all along.

Given that you'll never be able to have 100% confidence in the numbers, I'd suggest option #2, as it will be a lot easier.