Golden Cheetah FTP test

matthewbward

 Hey guys,

I'm brand new to Golden Cheetah.  I imported my FTP test from Poweragent (via a TCX file) and want to calculate my NP.  I think this is the xPower in GC but I can't figure out how to get the xPower from 3 intervals (20', 2', 20').  I highlighted them all in the Intervals window but can't get any further.

Thanks for any help!

Matt

 

Tom Glynn

I'm a little bit of a Golden Cheetah newbie, but you can locate best times. Find the 2 best 20 minute intervals and then find the best 42 minute interval and that should get your answer. Go to ride summary and then at the top menu, pick "Ride" and "Find Best Interval".

I've been using WKO for 6 or 7 years and just starting playing with GC. WKO seems to be much better for its ability to select ranges easily. I'm still learning and there may be an easier way.

My understanding is that in the upcoming version 3 there will be more of the Coggan power jargon like NP and TSS.

matthewbward

Yup, that does it. Seems kind of hacky though. But on the 1st tab, the new 42 minute interval shows up with an xPower. The xPower is about 2 watts different than Poweragent.

William Jenks

You can also get to a contextual menu that gives you the best 42 minute interval by right-clicking (ctrl-clicking) on the ride in the list.

Your observation about xPower vs NP is correct...very consistent with what I see. This is because the formulae for xPower and NP use different averaging schemes, and xPower always comes out lower for intervals of any length.

Good news - GC 3.0 is on the way and will have NP/TSS/etc. You can download current builds (not quite ready for prime time in terns of running smoothly..but you can see what they are doing) from goldencheeta.org

Tom Glynn

@William,

thx for the ctrl-clicking short cut!

Also, some chatter on the google wattage forum a couple weeks ago talking about the NP and xPower differences. Looks like the spread can get pretty big on rides of several hours and longer. One guy was seeing +20 watt differences IIRC. My thoughts are to just use what you've got and don't get caught up in the minor details. Pedal hard and you get faster I guess!

William Jenks

There's no way the difference is 20 W if you ride steady-ish. No way at all.

xPower uses and exponentially tailing decay and if I remember right, NP uses a 30 second moving average (boxcar style). Because of the particular time constant that xPower uses, the "response" is a bit slower than NP. In other words, it tends to smooth out your power distribution a little more. Since they then use the 4th power of that smoothed data in the average to get your NP/xPower, having fewer high power data points more than makes up for having fewer lower data points in the calculation...and thus xPower is lower than NP. However, there's just no reasonable way the difference should be that large unless you're doing something like just stomping on the pedals for a few seconds over and over. That's the kind of thing you'd have to do...or maybe have a defective power unit that was throwing a lot of noisy data. (In the latter case, you would tend to "average out" the data spikes better.)

In my rides, I've seen up to a handful of watts difference, but 20 would require something like 30/30s or a crit ride with lots of jumps, I'd think.

astasic

 I dropped Race Day Apollo for that very reason. I just don't have time to go back and forth sending files to Dr. Skiba. I got tired of watching the wrong numbers come up in my workouts. GC is the same. I had RD for over a year. It did not use to be the case. Whatever "updates" they did, it buggered it up. 

Tom Glynn

@William,

not sure if you are a member of Google Wattage, but here is the link on the NP xPower discussion
http://groups.google.com/group/wattage/browse_thread/thread/cd5ad2af66a1fd2a