I thought I understood power....but no?

Dawn Cass

Hello all, I have been training with power for about 3 years and think I know what I am doing.  I certainly understand the impact it can have if you train with it and have seen great success by doing so.

My question lies in this:

Last training ride this past Saturday was at average speed 19.9 mph, average watts of 170...total 60 miles.

If I compare this to someone like my husband, he is running much lower watts for same speed output.  As alternative, I see other ladies doing the same...ie, same speed, running lower watts.

So my question is this...what is the difference?  Let's assume for this argument that the course is the same.  The only variable I can see is weight.  So if I weigh more...or my bike weighs more, I will have to exert more power to get the same speed as someone else.  Where this falls apart is in the case of hubby...he is obviously heavier than I am, so how does the math work.

Once I can figure out the difference, I can work on the right things.  If I need more power than I know what to do.  If I need to shed weight...on bike or me...got that however how much weight makes a difference?  Does carrying 1lb more really make massive delta in watts.

Sorry if silly questions however I still have 2 solid months of training to be had and really want to crack this!

Thanks for listening.  ;-)

jaleslie

Dawn....the simplest answer that immediately comes to mind for me in this scenario is that your PM is not accurate/calibrated (not the same as consistent).....or maybe their PM is not accurate/calibrated.  

For example, if your's is 20W "low", then you'll go as fast as your twin on the same bike/conditions with a PM that is accurate/calibrated but at 20W lower than her.  I have checked my PT G3 once (when I first got it and was sad to see that my FTP was not actually what trainer road calculated) to make sure it is "accurate".  I found a youtube video showing how to do it....hanging a weight off the pedal with crank horizontal and back brake locked, then plugging some numbers into the calculator...can't remember the details, but it was within the acceptable range of error/accuracy.  

Furthermore, earlier this year I noticed that I seemed to be losing watts (while still training consistently) and the calibration number that usually shows up when I calibrate the Garmin/PT had changed quite a bit (>525, instead of ~506).  Sent it back to Cyclops and they "recalibrated" (or rebuilt) it and it was back to it's old self.  

So, if all your riding partners are lighter than you and riding similar bikes and you are seeing much different watts in the wrong direction, your PM may be "off".  

Of course, it doesn't matter except for bragging rights, as long as it is consistent (the speed will take care of itself as you know).  

HTH.  

Peter Greagg

Additional factors that potentially could explain the disconnect are differences in all up weight, differences in cDA (wind resistance), and/or differences in rolling resistance.

Steve West

Could be calibration. Or, could be postion. Aero trumps watts all day long. Seemingly small changes in cDA make big differences in speed at a a given power.

tim cronk

Great answers and most likely ... calibration - are the PM's the same and calibrated correctly .... w/cda - position/drag on the bike and maintaining that position

some other factors to consider
1. bike handling - maintaining momentum thru corners etc ...
2. make sure to compare AP to AP , not NP to NP .... AP is the REAL average power that moves you down the road ....
3. check distance measured by head units to make sure its the same.... just a few tenths of a mile difference can vary the avg mph quite a bit, specially shorter rides
4. any stopping at lights etc ? using auto pause or manual ? do both people operate the head units the same?

Rich Stanbaugh

This is a really interesting topic Dawn. All of the answers above are good ones. I would start by rechecking the numbers. Make certain that the "real" vs the "model" numbers" are the same/different. Distance, Time, Average Speed and Average Power are "real" if you start and stop a ride together with someone and the GPS's are on/off for the same time periods, the distance and average speed should be pretty close.

Next, make sure that both GPSs are set up to include zeros in the calculations. This makes a huge difference. If one of the units includes zeros and the other does not, there will be a substantial difference in recorded power, with the one that does not include zeros having a much higher power number (always include zeros).

If the distances, times and speeds are nearly the same, and both units are set up to include zeros, then all of the above advice will get you to the right answer.

Kane Murphy

All good answers. Don't underestimate the difference a good set of race tires and latex tubes can have over regular tubes and training tires. 10 - 15 watts on the road easy assuming they are both inflated properly. I would have never imagined until training on a set of rollers with a power meter. Race type setup and I don't have enough gears on my bike to get the resistance high enough for anything other than just riding along effort. Thorn proof tubes and gator-skins means I am in close to FTP while in the easiest gear on my bike.

Nate Parady

"Does carrying 1lb more really make massive delta in watts." would say that it impact speed, not watts.
It could be a calibration issue, but if its off by just a few watts what does it really matter as long as your readings are consistent. I suspect every PM has a variability of accuracy especially across different brands. just a guess.
Is really everything else the same? are you guys on the same training course? So many factors besides watts impact your actual speed i.e. bike setup, total weight, road pavement type, WIND, tires, tubes, how you actually ride the course...

Shaughn Simmons

I think everyone has nailed down the factors:

Calibration

W/Kg ratio - weight

Aero - body position - wind resistance - streamlined bike setup, wheels, etc.

V.I. - Variability Index - holding a constant power with no spikes, limited stops etc - will make you go faster at the same power output

SS

 

Dawn Cass

Thanks all, this has been extremely helpful information.....I love it.

Perhaps another silly question cDA - what does it stand for? Wind resistance. If so...agree this would be a factor. In the example I gave above on the training ride...no wind that day.

Calibration...good one all. I actually got to thinking about that after I wrote the post. I don't do it regularly to be honest. I have a Quark PM. Will need to double check everything is ok.

Tim - thanks for the points...like it. Rich - never checked the "zeros"...probably should!

Other things to work on, in general then....fitness (of course!)....others:
1. Body position - have had same set up for 3 years...maybe time for a tweak
2. Wind - can't really control nature so fitness plays into this one to overcome
3. Wheels - Have Zipp's, just bought a wheel cover for the back, and looking to replace my tires as others are worn
4. Bike set up - I have a large speedfill water system on the down tube. Been thinking about BTA setup instead. Does anyone have opinion if there is more aero in either?
4. Bike set up - How would I check other aero factors?
5. Weight/kg ratio - agree on that. Am a few kilo's up where I should be due to taking a year out for injury...and now just coming back. Working to get down to race weight now.

Any other thoughts...throw them my way please....I really want to nail this years race! ;-)

Nate Parady

"2. Wind - can't really control nature so fitness plays into this one to overcome"

keep in mind, the goal during a race is to be super steady. Some folks don't even look at MPH on the dial because they really can't control that result. all you can really control is your effort/watts. My last IM had me doing 155 watts. With a head-wind of 15MPH sometimes I was going 10-12MPH on a very flat course pushing 155 watts. The tail wind on the same watts was upwards of 25+MPH. Overall VI for the race was 1.02...

There were many other athletes fighting into the wind trying to keep their speed up while I mostly ignored the wind all together focusing on keeping my watts steady.

novaavant

Dawn,

Here is probably more than you ever wanted to know about cDA: http://www.cyclingpowerlab.com/CyclingAerodynamics.aspx

Dawn Cass

Thanks Nate, good point.

Attila - good link....will have a nice read of it this evening.

Dawn

Coach Patrick

Dawn, all of this is great...and the learning is good. For me, however, the stimulus is wrong. I don't think you can ever really compare watts with the person next to you and, based on their number, determine something of value about your number.

Example...we are riding together and we are having a great ride. Fast, hard...really pushing. Smiling in our suffering. Then you look at my PM and see I am only pushing 100 watts, and you throw your hands up saying this is bull$hit, how come your 100 watts let's you go this fast Patrick?!

My 100 watts has nothing to do with how hard you are riding.

You can't compare my 100 watts today with your watts as compared to all your previous rides (your 200w today vs your 195 watts last week is much more relevant).

You have no idea about the state of my PM or my equipment or how I am turning the pedals...you just know I am next to you.

So like race day and the Four Keys, I recommend you focus on what you can control, making sure your set up is consistent, reliable and accurate...and that you use that framework to get faster and work hard. After that, everything else will take care of itself!

William Jenks

I think about data professionally almost daily, so I have a couple of thoughts here. While I generally agree with Patrick, that you don't want to put an emotive value on what you are doing, number wise, your question is a real one.

The first question is data accuracy, and that's been brought up before. If you have reason to believe your data are inaccurate (which you suggest in your original post), the first thing is to check the simple stuff like calibration and zeros ("averaging zeros" is the generally accepted correct setting but will lower the average watts shown, relative to someone else's data who excludes them). The second thing is a legitimate control experiment. And I bet one of your friends would loan you their power tap wheel and computer for a day to see if you're getting the same kind of numbers you're used to. You can't do a perfect A/B test unless you're using a different (e.g., crank) measurement, but you can still just to a great guesstimate of what your watts would read based on your effort. (DC Rainmaker talks about doing multiple measurements at once, but 99.99% of us don't have all those different PMs at once!) You want to do your experiment with your computer, not theirs, in case they have it set up for a funny kind of data averaging. You have to take that possibility out of the mix.

Now, let's say that the PM data seems accurate, or at least consistent, i.e., you figure out there's nothing needing repair or fixing.

Then realize two things, both of which have been discussed, explicitly or implicitly.

This MAY give you information that there is speed to be gained from a better aero fit or from some of the technique matters mentioned in other replies if you think you are going "too slow for your watts" relative to similar sized people. That's fair and entirely possible.

The other thing is what Patrick brought up, but I'll say more explicitly. In a sense, the accuracy of the number relative to someone else doesn't really matter, as long as the number is reproducible. We use Watts, but we could use foot-pounds/second, or BTU/hour, or any other designation that would change the "number"...We could bury a little thing in the software just to take Watts and multiply it by 2...so we could feel better about having a bigger number. For purposes of training and racing, what matters is that (a) you train to improve your OWN reproducible power number; (b) you use that power as efficiently as possible (e.g., aero); and (c) that you use the guidelines of percentages of powers for the training and racing to accomplish the first two things. 85% of your measured FTP is always 85% of your measured FTP as long as your number is proportional to some abstract reality.

So my take is that your question is good and fair, and there's reason to check... but once checked... Patrick's right.

Rich Stanbaugh

Did you check to make sure both devices include zeros in the average power calculations? This is a setting in Garmin devices that gives you the option of including or excluding zero power (not pedaling) in the calculations. If one device includes the zeros and the other device does not include the zeros - the one including zeros will have substantially lower average/NP power numbers than the other.

There is a lot of good advice above. Could be a really simple answer like a setting though.