HMF

I don't get xPower in Golden Cheetah. I went out for ZCI intervals tonight, and paced them perfectly, no big spikes anywhere, just a bunch of flat tabletops. Yet xPower is 10 watts lower than average power on each interval. Is it because of the length of the interval, or what?

plantrob

I've never seen xPower < AP. Only thing I can think of is that since xPower uses a rolling average power, it would take in some of the low-power data from the rest interval. Normally, I would think that effect would be outweighed by the variability that tends to make xPower > AP. But since you paced your intervals so well, it's possible that it works out the other way around in this case. I think the averaging duration is ~30 seconds, which is 1/10th of your ZCI interval. A reduction by 10W (presumably, <3% of your power during the work intervals) is possible, especially if you took your rest intervals really easy.
That's just the mathematics. A better answer might be that xPower isn't particularly meaningful over a 5-minute interval. Stick with AP for short-duration power analysis.

Jsiegs

I've seen xPower below Avg Power. If you're at 100 w and your interval is 200, and well placed, it takes some time for your exponentially weighted moving average to rise to 200 watts, so for the first part of the interval, your EWMA is <200 (this is what is being averaged for xPower I believe). 10 watts seems high for a 5 minute interval, but I see them equal or xpower slightly lower on well paced intervals (usually on the trainer, I'm less well paced on the road).

That would be my guess, if I remember from reading Skiba's books correctly.

waterrockets 

The big difference between XP and NP is that XP uses an exponential moving average (from the last 25s), where NP just uses the moving average (from the last 30s). I would need to look at the source code to know the value of α​, which is the weighting factor for each sample in the EMA.

echappist

correct on both accounts. NP & XP don't start to tabulate until the 30th second (25th for XP), so that chunk will be missing

also correct that NP is useless for duration < 20 minutes

caloso

Got an email from Training Peaks:

Is this a new feature?

LeeRoySD

It must be. I just got one as well for the first time today. I uploaded a 3x3x2' peak and fade workout and it suggested I drop my threshold by 32 watts. Really makes me want to upgrade so that I can get some more of their "analysis"...

Creatre

Wish it was that easy to get a 40w threshold increase.

caloso

I think what they were telling me is "You're cheating to get a bigger TSS, so knock it off!"

shovelhd

I think they're right. You need to bump your FTP, by a little, at least.

Smallguy

Newbie question

when someone says that person has a 1200W sprint are they talking average or peak ?


Also last night I found the interval feature on my Garmin under workouts. I was doing 250meter sprints then a 1.75km recovery. What I did was reset my Garmin after each set. I might be doing this incorrectly but it does work but am I throwing off my TSS. Each of my sets were in the 24-26 range so I can add them up but wil lthe nubmer be the same as if it was one workout.

shovelhd

Peak. After the peak, it goes in terms of 5 second power, 10 second power, 15 second power, etc.

brian416

You don't need to reset your Garmin, just use the lap button, it will split up your workouts and still have it all in one file

Smallguy

^ Thank you

GirlAnachronism

Many of the display metrics also include a 'lap' option. So, for example, if you're interested in seeing your lap power, you can set it to show 'Power - Lap' and it will display whatever you're averaging since you last hit the 'Lap' button. That's also especially useful for displaying time when you're doing intervals, so you don't have to keep track in your head of when you started and when you need to stop.

rbart4506

Looks like my PT bearings may be on the way out, Noticed last night when moving the bike that there's a slight grinding sound coming from the rear wheel. My guess is the bearings are on the dry side. I need to remove the wheel and spin the axle by hand to check for roughness/resistance.

I'm thinking of attempting this one myself since the wheel is out of warranty, bought from Rob a couple years back. I know I risk buggering the calibration, but if I do then I send it in and wait for the bill.

I've got the bearing specs, but just curious if someone's knows where there's instructions on how to do this...Or what not to do so it doesn't get screwed...

I seem to remember a couple post in the 33 a while back from someone who did this exact thing.

ericm979

It's not that hard. There's a set of instructions/pictures out there.

rbart4506

I've been looking, but haven't found anything yet...video/picture wise..I'll keep searching...

brian416

There are some directions here on WW for replacing the bearings

rbart4506

Thanks Brian...I had found those...It really is pretty simple to get apart...

My freehub bearings are fine so I will leave those as is...

Now it's a matter of sourcing the bearings locally and pressing them in...I also found a youtube video that showed how to remove the axle and install the NDS bearing and axle...Looks easy enough...

I have no issues paying Saris to service the unit if there is actually something worn, but $300+ (plus the down time) for a bearing swap is a bit much....

waterrockets 

$300 is a lot, but it's more than just bearings. When I sent mine in 3 years ago, they said they would replace everything I sent them, so I sent HR strap, Cervo, harness, and what I got back was everything brand new except the hub shell. They even upgraded my axle to the new multi-piece design (I can pull cassette off bare-handed, as freehub comes with it now)

rbart4506

Got the bearings replaced for a grand total of $35 and about an hour of my time...

Took the bike out today and everything seems to be working fine...Numbers make sense...

The only time I'll send the PT in is if the thing is actually not working...

The big deal for me is turn around time as well. Here in Canada the distributor is a little slow on the service and the last time mine went in I was without the wheel for almost a month...That's ok in the fall, but not now in prime racing/training season...

orcanova

When iBike first came out I read a lot of scepticism on this forum. Given the current generation of iBike, is it a worthwhile power meter at this point in its development? I ride a road bike, a TT bike, a cyclocross, and a roadbike on a LeMond trainer. I'd like to transfer a power meter easily from bike-to-bike, and am considering an iBike Newton+ (which supposedly works on a trainer).

Also, I currently use a Garmin 705 with hrm, and would like to continue recording that data (I suppose I could always stick it in my jersey pocket on a ride rather than having two devices mounted on the bars). Can the Garmin receive the iBike power data via ANT+ so that its all in one file?

Finally, since the iBike uses wind as factor, is there any way I can determine drag with different positions on my TT bike to determine my most aero position?

Smallguy

what are realistic percentages for improving each of the power metrics we use?

reason I'm' asking is I'd like to set some realistic goals for next year for peak, 5 second, 1 minute, 5 min and 20 min.

My soon to be wife says I'm crazy and set unobtainable goals so I'm asking you crazies...lol

right now my bests are 1125, 1063, 470, 293, 260 respectively.

I've never tested my peak, 5 second and 1 minute the numbers just from a rides and intervals I've done.

mattm

Golden Cheeta q: where's the equivalent of the PMC in WKO?

Does it have the graph tracking the equivalent of CTL & TSS/d (bikescore), etc?