I’v been looking at new wheels and I’ve been trying to figure out what the aero data I am reading actually means. I understand less grams of drag is good, but I have no idea what yaw is, or what affects the amount of yaw. I’ve done a little Googling around and haven’t really found any answers. Example of a chart I have not idea how to read: http://www.flocycling.com/aero.php
This link may help a little.
http://austintriathlonstore.blogspot.com/2014/06/2014-texas-state-time-trial-champion.html
Depending on the wind conditions, course terrain, and your speed you will spend various amount of time at different yaw angles. Pros tend to spend more time at lower yaw angles as they tend to go faster than us normal humans. The drag charts for wheels are typically for the wheel only (not as part of an overall bike) so I wouldn’t expect a wheel to actually give you lift (negative drag) when paired; however, if you look at several of your races and see that you might spend a lot of time in certain yaw angles it may help narrow down your wheel choice based on the manufactures (or better an independent studies) aero data. Not sure if that helps, but the blog post above goes into it a little bit as well.
yaw is pretty simple. It is the experienced wind direction by the rider. (0 degrees = headwind, 90&270 = side, 180 = tailwind)
If there is no wind, but you are going 20mph…you feel a 20mph headwind vs. standing still. - 0degrees yaw
If there is a 10mph headwind and you are going 20mph…you feel a 30mph headwind vs. standing still. - 0degrees yaw
If there is a 10mph tailwind and you are going 20mph…you feel a 10mph headwind vs. standing still. - 0degrees yaw
Then…things get all trigonomic when you factor in sidewinds. There are plenty of yaw calculators that you can play with to get a better idea. But in general, the faster you ride relative to the sidewind…the less of a sidewind (and more of a headwind) you will actually feel. ex: If there is a 5mph sidewind and you are going 15mph( - 18degrees yaw)…you feel it a lot more vs. if you were riding at 25mph ( - 11degrees yaw).
So, the charts will show that wheels deliver varying amounts of drag at different yaw. As mentioned, a pro rider (fast, less yaw) would be more interested in the numbers closer to 0, while the higher yaw numbers will be more relevant to slower riders. Additionally, consider the extreme examples like windy courses (higher yaw) and indoor tracks (very low yaw).
Looks like you have gotten some good yaw info already.
There is a rule of thumb that helps to get an idea of what the grams of drag will do for you:
50 grams of drag in the tunnel @30mph ~= 5watts @ 30mph ~= 0.5seconds saved per kilometer at any speed
So for example, if you think a wheel will save you about 50 grams of drag on average, that would be ~20 seconds on a flat, straight, 40k olympic tri bike course. Somewhat less if it is hilly or has lots of turns.
This isn’t exact but it is close approximation. So if you see something that supposedly saves 10 grams of drag for $1,000 you can think “oook, that isn’t many seconds, screw it”.
Some good info, thanks for the help. I *think *I’ve got a decent understanding of what I’m looking at.