Using analyticcycling

whoawhoa

When using the power given speed page on ac,

1. Is there a good way to estimate cda? Say a formular for fa and a common cd?

2. If I am trying to get an idea of short duration power by doing a, say, one minute effort up a steep hill, should I start the hill at a speed similar to what I will hold during the effort to minimize acceleration/deceleration?

frenchyge

I'd say frontal area would be easier to determine directly, then solve for Cd. You can measure frontal area with a digital camera or videocamera setup. As long as there's something in the frame like a yardstick to establish the scaling. Solve for Cd using a coastdown measurement or power at a steady speed.


Definitely want to hold speed constant. Speed changes will throw off your AC.com calculations significantly.

RapDaddyo

Speed on a known grade upgrade is probably the best way to estimate power without a power meter, at any duration. But, if the grade varies, even by 1%-2%, be careful about using the average grade because the average grade will understate the "effective" grade for measurement purposes. Think of a rolling, close-loop course. The average grade is zero, but the higher power required by the upgrades is not offset by the lower power required by the downgrades, at least on a physiological basis. Look at the weighting algorithm in NP. And, unfortunately, the highway engineers never got the message that you need a constant grade upgrade for testing purposes. So, this was never a design goal. You minimize the problem the shorter the duration, but be careful in choosing your test road.

rmur17

(1) FA formula's yes but for n=1 I don't think they're of much use. CdA is of course what matters. For an aero position that could be 0.2-0.3 or even higher if you're a large bloke. For a tops/hoods climbing position something around 0.4 is in the ballpark or some 40% higher. I'm around .275 fully 'aero' (like a barn door!) and ~0.40 on the tops (at a lard-like 85 kg mind you)

(2) Yep. Constant speed to make the static ACC formula's work ( or zero delta KE across the interval). If you go long enough however the impact of delta.KE approaches zero

(3) Time to ante up (or have your parents do so) for a real PM. You can find quite decent, lightly used PT Pro's around for maybe 2/3rds of retail. I have two units and find them great ('cept in heavy rain). Folks often buy toys and carelessly discard them

rmur

whoawhoa

I guess all formulas work beter for a population then an individual.


Already saving. Just have to win a few races this spring! Is there any reason to go with the pro over the standard?

frenchyge

Pretty sure there's a thread specifically about that. Greater memory and better interval display come to mind off the top of my head.

rmur17

I like yellow ... and memory capacity and better interval functionality. I think the SRM is best of course but the prices just ain't coming down on those puppies. The SRM interval function: (1) Turn it ON (2) Do your interval (3) Turn it OFF (4) have your interval Stats flashed in your face ... seems perfect to me. But for an extra $1.5-2.0k ???

rmur

whoawhoa

What about the smoothing feature? Does power jump around too much without it? I don't think that was mentioned in the other thread, but I just skimmed it.