Originally Posted by
Racer Ex
There's seldom high precision in field testing (see external conditions)..."real world context" by your definition makes noise a good thing, which it's not. It's dog poop on the rug. "Real world" is, to paraphrase Chung, a red herring unless you apply it to yaw. Which you can't field test.
Having seen the variability of results from 3 different tunnels, and having run 100+ field test runs with a couple of riders, it's my experience that it's pretty rare for the field to hit the repeatability of the tunnel (and this is coming from someone who doesn't pee or drink during tests to keep the rider weight as static as possible). Can it be as precise, or at least close? Sure. Every time on any given day? Absolutely not.
1. I'm absolutely not saying that all field tests are always better than any tunnel test every time on any day -- that's a straw man because you'll never find in any thing I've written that I've ever made that claim. I'm saying that properly done field tests (and "properly done" is key) can be high precision. If you've been getting dog poop field test results, then your field test techniques are dog poop. How do you explain a CV on the estimated CxA of 0.3% otherwise? That's a sd of .0006 m^2, i.e., for that test I could reliably distinguish a change in CxA of around .001 m^2 -- "reliably distinguish" in the conventional 95% hypothesis testing sense. That's about the size of my thumbnail. When you go to the wind tunnel, do they give you a 95% confidence bound on your results? What is the CV on your wind tunnel estimates? After you tell me that we can do a little more discussion on noise and dog poop.
2. I'm also saying that equipment exists that allows one to test at variable yaw, although that equipment is not generally available.
3. As I've said elsewhere, a wind tunnel works when the conditions outside are not conducive to field testing; a wind tunnel is faster than field testing; a wind tunnel can (often) be more convenient than field testing; if you don't have the right equipment, a wind tunnel lets you test at non-zero yaw; and a wind tunnel is way more expensive than field testing. I've also said that the key to a good testing protocol isn't just that you can get an answer out of it -- it's that you can tell how good (or poor) that answer is. If you've done 100+ field tests and got dog poop results out of them then I'm thinking maybe those methods you're using aren't the best use of your time.
4. BTW, I can produce the same level of field testing precision even without a power meter -- the testing is slower and more tedious but the precision is the same.