Help understanding Power data - Updated 26th Feb

delvsie

Hi all,

I have recently started using a Powertap Pro+ hub. I performed the FTP test as described in the Training and Racing with a Power Meter, on a turbo. I calculated my FTP to be about 261. However, I did the Kentish Killer (70 mile route) yesterday using my new Power Meter. I have uploaded the information to my trainingpeaks account and am a bit confused with the stats that I am seeing. For example my NP for my peak 60 minutes sector was 316 watts. The book also states that the NP over a 60 minute hard ride is a good estaimate of your FTP, hence my confusion.

Can anyone advise / help?

Update: Just finished the Hell of the Ashdown Challenge. Not too bad a time - 4 hours 10 mins. Reset my Power options on my Garmin 705 as requested in the below posts. Autopause off; Zero Averaging On; recalibrated as instructed. My Peak 60 min stats state that NP is 309. My overall ride stats are NP 291; AP 233. As the stats are similar to my ride last week can I assume that my FTP is around the 310 mark, or do I still need to do more tests?

Thanks.

Thanks. :?

Alex_Simmons/RST

First things first - let's check that the data is accurate.

It may be, for instance, that one one (or both) of those rides, the torque zero was not properly set, which will mean the power data is inaccurate.

Are you checking and setting the torque zero before every ride?

delvsie

I am. I tend to work harder on the road than on the turbo...

delvsie

... I say that I am. I always "wake" the hub up by spinning the wheel, and the check the ANT+ settings in my Garmin 705 (calibrate Power). The reading is always around the 515 mark. Is this what you mean by setting the torque to zero?

amaferanga

A lot of people find power on the turbo is lower than what they can do on the road, myself included (even with proper cooling). I'm down about 20W on the turbo. Your road/turbo difference doesn't sound right though. Do you have your Garmin set to auto-zero as well as manually zeroing at the start of each ride?

Your numbers for the road ride sound high - how much do you weigh? Unless you're on the large side then 316W NP for an hour should see you averaging well over 20mph on most British roads so that might let you check for consistency and how believable the numbers are. What was your AP and NP for the entire ride? And how do the numbers compare with other rides you've done? Is this ride an anomaly or is it consistent with other hard road rides you've done?

delvsie

Hi amaferanga, i think my Garmin is set to auto-zero (can't check right now, not near my bike). I weigh 209lbs. AP for the ride was 227, (256 pedalling time); NP was 276. The ride took me 4 hours 26 mins and had a total of 6,000+ feet of climbing over a 70 mile route. This is the first long ride that I have ridden with the Powertap hub. I must say that this ride was probably the hardest mile for mile that I have done.

jibberjim

Auto Pause is still turned on I bet? (this inflates NP in WKO)

delvsie

That's true, I do have auto pause on. Should this be turned off? I'm not using WKO+. I am using Trainingpeaks and the Powertap software from CycleOps. Would auto-pause really affect the stats?

moonshine

do you have zero average on? you should have it set to Zero average.

Alex_Simmons/RST

ok, well a few things then:

indoor trainer power v outdoor power - often people cannot sustain same level
making sure torque zero is set
auto torque zero doesn't always work if torque zero value is significantly out to begin with
auto torque zero requires periods of sufficient coasting time to work, which may not occur on an indoor trainer
auto pause as suggested may impact power stats
Garmin smart recording can screw up power data, disable it

amaferanga

moonshine wrote:

do you have zero average on? you should have it set to Zero average.

That only affects what is displayed on the Garmin, not the data saved to the ride file.

jibberjim

Yes Auto Pause will impact the NP calculation in WKO or Training Peaks, turn it off, otherwise you cannot have NP, sorry you're not quite as strong as you thought - probably still stronger than your 260 though.

ajmitchell

hi, I suggest you repeat a few times indoors and out over 60mins; that will soon tell you what your NP is and iron out any fluctuation. BTW I think that it is quite possible to have 2 seperate figures one for indoor and one for out, depending on conditions.

delvsie

Thanks for to everyone who has responded to my posts. I will turn auto-pause off and see how this affects the data and re-check all of the other settings. I guess the best thing is to do as ajmitchell suggests and get out and do some more rides and see what the results are. It should be fun :-)

Thanks again.

delvsie

posted additional question in my original post above

amaferanga

What was the AP for the 309W NP hour? From the other data it looks to be highly variable so probably not the best estimate for FTP. Do you feel that you could actually ride at a constant 310W for an hour?

At least you now have some good data and I'd suggest that your FTP is very likely higher than your original 261W estimate. It might be 310W even. Just keep riding and collecting data and you'll soon know if you've got a good estimate for FTP.

delvsie

amaferanga wrote:

What was the AP for the 309W NP hour? From the other data it looks to be highly variable so probably not the best estimate for FTP. Do you feel that you could actually ride at a constant 310W for an hour?

AP for this weeks peak 60 mins was 257, last weeks was 267. Not sure about maintaining 310 W for 60 mins, however, isn't that what the stats suggest? Both courses where hilly which allowed for fairly good recovery whilst going down hill. I also know that my power readings whilst climbing tend to be considerabky more than 310W. Is it possible to have different readings for different terrains?

Alex_Simmons/RST

delvsie wrote:

amaferanga wrote:

What was the AP for the 309W NP hour? From the other data it looks to be highly variable so probably not the best estimate for FTP. Do you feel that you could actually ride at a constant 310W for an hour?

AP for this weeks peak 60 mins was 257, last weeks was 267. Not sure about maintaining 310 W for 60 mins, however, isn't that what the stats suggest? Both courses where hilly which allowed for fairly good recovery whilst going down hill. I also know that my power readings whilst climbing tend to be considerabky more than 310W. Is it possible to have different readings for different terrains?

It suggest that your FTP is closer to 310W than it is to 257W, and probably at least 295W.

Some people can hold more climbing than on flatter terrain, but that's more a matter of practice, training and concentration in keeping the strain on the chain when on flatter terrain.

GiantMike

delvsie wrote:

Update: Just finished the Hell of the Ashdown Challenge. Not too bad a time - 4 hours 10 mins. Reset my Power options on my Garmin 705 as requested in the below posts. Autopause off; Zero Averaging On; recalibrated as instructed. My Peak 60 min stats state that NP is 309. My overall ride stats are NP 291; AP 233. As the stats are similar to my ride last week can I assume that my FTP is around the 310 mark, or do I still need to do more tests?

Thanks.

If your peak 60 min within a 4 hour ride was 309W then that is good data in a realistic scenario. However, I'd suggest that your Mean Maximal Power is above 309W because if you can do 309 in real-world situations you could probably do more in 'ideal situations' (such as a decent warm-up and a 60 min all-out effort on a safe route without traffic, junctions, other riders etc.

A 20 min Turbo test may ellicit more information, BUT as you're likely to be hotter than on a road ride your power will probably be down on your true performance anyway.

For reference, my hot and sweaty 20 min Turbo session shows I can produce 323W AP (and 322W xPower). From this I would derive my CP60 to be 307W but I have never got anywhere near this on the road. On the road (with all the distractions and impairments listed above but also including rough roads) I have a recorded CP60 of 289W (xPower 290W) in cool conditions. Threfore, as your proven CP60 is 20 above mine, I'd suggest your POTENTIAL CP60 is around 330W (i.e. approx 20 above mine).

I don't think you'll ever get a true figure of your FTP. Each time you test the conditions will be different and your performance will be different. If I were you I'd settle with a 'guestimate' of 320-330W and derive power zones from that. Or, if you're keen to keep on testing, find a distraction-free road and do a real test minimising the various effects likely to affect performance.

What's your weight by the way?

amaferanga

I find NP for variable efforts (e.g. races or undulating terrain) is really poor at predicting FTP. xPower on the other hand always seems lower for such efforts and for me is more consistent with what I can do in steady state efforts.

Since the OP isn't sure that he could do a steady 310W for an hour then it seems unlikely that 330W would be a good estimate for FTP. I know we're all different and that, but for me if I can't do 2x20 at FTP on the turbo then I'd say my FTP is set too high. If 2x20 at FTP on the turbo was comfortable I'd say my FTP was set too low (NB I can't do 60min at FTP on the turbo because I always use my 'road' FTP even through the winter when most of my training is on the turbo as using a lower 'turbo' FTP seems like cheating)

GiantMike

In the edit of the first post the OP states that his peak 60 min NP is 309W recorded as part of a 4 hour ride.

I didn't realise that NP was different to xPower. Is the calculation different? My xPower and AP are usually quite similar (and I can explain the differences) but I've never used NP.

amaferanga

GiantMike wrote:

In the edit of the first post the OP states that his peak 60 min NP is 309W recorded as part of a 4 hour ride.

I didn't realise that NP was different to xPower. Is the calculation different? My xPower and AP are usually quite similar (and I can explain the differences) but I've never used NP.

xPower and NP are similar, but xPower uses an exponentially weighted moving average. I've had NP's of 20-30W higher than xPower for road races and typically for interval sessions NP (for the whole session) will be several Watts more than xPower. E.g. I just picked the first race I could find from last year: 95 mins, AP 277W, xPower 299W, NP 321W (my FTP at the time was no more than 310W)

delvsie

GiantMike wrote:

What's your weight by the way?

My weight is 207lbs.

I have a question what is xPower and how is it calculated?

doyler78

delvsie wrote:

GiantMike wrote:

What's your weight by the way?

My weight is 207lbs.

I have a question what is xPower and how is it calculated?

You'll find the full discussion of it and it's associated metrics here:

http://www.physfarm.com/bikescore.pdf

delvsie

Read the article. Can honestly say that I didn't understand a lot of it :-)

I will continue to enjoy my riding and post back new data as and when I get it. Once again thanks for all of the comments / advise, etc. If anyone else reading the posts has other information to help with my understanding I would be very grateful to receive them.

Thanks.

GiantMike

I think the key point is that there are a lot of different measurements of power and lots of factors that affect each. Pick one you like and use that to compare your improvements over time.

Power-to-weight ratio is also useful to track (Watts per kg is the usual version) as it takes into account the benefits of slimming down as well as improving power.