Stability at higher speeds?

[mds]

On my climbs, I find my iSport's power display very stable and with some concentration it is not too hard to hold a particular power all the way up a climb and match a previous climbing time quite accurately. At higher speeds, however, on flats and gradual ascents and descents, the power display seems to wander quite a bit more. It seems to correlate with my pedal force less than when climbing. Even when I concentrate hard to hold a particular pedal force constant, the display will wander at times, like maybe +/-30 watts, sometimes more sometimes less. Is this wandering normal for higher speed riding?

[Russ]

Hi mds,
One large contributing factor, probably your answer, is the air drag component increasing with the cube of the speed. This means that a small change in air speed due to wind variations and gusts show up large at high speed and very small at low speed.
At high speed, your wind offset, wind cal and CDA become more critical for accuracy as well.
Russ

[coachboyd]

Watts are definitely easier to hold steady at slower speeds. What is happening is your body has a natural tendency to want to slow down when you are pushing yourself. You will very quickly sense that your speed (and watts) have lowered and overcome that by pushing harder.

At speeds, it takes a little bit longer to realize that you have slightly slowed down. Even though it's small changes in the speed, it can really lower your average watts and make them less stable. It's really something to work on to hold watts stable on the flat just like on a climb.

[mds]

Russ and coachboyd, thanks for your comments. The power variations do seem to occur in gusty conditions, so maybe wind variations play a part. On my climbs, say at 85% FTP, I can get a 30 watt variation in power only by changing my physical effort by a rather large amount. There is no confusion here - 30 watts up or down feels physically very different to me when climbing. But on the flats at higher speeds, again at 85% FTP or as close as I can get by mentally averaging the variations, when I see a 30 watt variation, my physical effort may not have changed much at all, if any. But 30 watts is 30 watts, isn't it? I think I should be able to feel the difference in effort the same way no matter if I'm climbing or on the flats. But maybe I am mistaken and this is all in my head. I'll keep working on it.