In Reply To:
In Reply To:
According to Robert's presentation, a 1% change in Crr is ~equivalent to a 0.3% change in CdA. That would mean with a base Crr of .0040, a change of Crr of .0005 would be a 12.5% change. That would represent a (12.5 x 0.3% = 3.75%) 3.75% change in CdA. If your Cda is .200 -.250 m^2, that would be a change of ~.008-.010 m^2.
Shouldn't the ROT be more like .0005 Crr = .010 m^2 CdA? = 10W = 1 s/km?
I have to clarify that. That particular relationship depended on those data. In other tests I've done under different wind and slope conditions, I've gotten different relationships. Basically, Andy's ROT applies at the speeds we often see when TT'ing on flat ground. If you're riding at a different speed you're going to be on a different part of the curve.
OK...and I understand. In fact, if I just quickly figured out the "power cost" for incremental changes in Crr or CdA for my own weight and speed, I get basically .0005 of Crr = 5W = .005 m^2 Cda.
However, if I go into one of my test runs and vary the assumed Crr by .0005, I need to "adjust" the CdA by ~.010 to re-level the plot.
I guess what I'm really interested in is if somebody assumes that their Crr is lower or higher by a certain amount, how will that affect the CdA determined using the VE "leveling" approach? ;-)
edit: Never mind...the test run I had to "adjust" by a higher amount was a run I did on my road bike when testing tire pressure changes. CdA is MUCH higher and speeds slower on that. Definitely on a "different part of the curve" for that. When I pulled up my P2K run from last week, your ROT of .0005 Crr ~= .005 CdA held. Sorry 'bout that....
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