so reading the tri-rig article and the conclusions that Flo have come to - Simply put, **yaw angles of 0-12.5 degrees are nearly 9 times more likely **- does this mean that some assumptions about which frames are the fastest may be predicated upon some false assumptions?
I just wondered based on that article.
I would go even further.
I have not read all of the new flo info, but looking at their bike test rig, it appears that the test apparatus may accurately measure the relative airflow and the yaw on the fork, handlebars, and the front wheel. But the yaw on the rest of the bike (the frame) and the rear is considerably lower than that experienced by the components attached to the steering column. So the data for the rear of the bike would favor low yaw conditions even more.
So, something else to chew on.
not for some of us. I haven’t personally cared about frame or wheel behavior above 10deg for a long long time, or since I started caring about it at all.
This isn’t anything new, 0-10 is where it’s at.
http://engineerstalk.mavic.com/yaw-angle-measurement-in-real-conditions-on-kona-ironman-course/
I’d go further to say +/- 5 degrees. The Kona sweep showed 70 % at less than 10 degrees (one of the windiest courses). The France sweep showed 82% at +/- 4 degrees.
Simply put, no. This is nothing new. Which is why Cervelo is so popular among cycling analysts as they always make sure of low yaw performance.
I often re-analyse magazine or brand data to correct the yaw assumptions - http://speedtheory.co.nz/triathlete-magazine-windtunnel-testing/
When I worked for a wheel brand nearly 10 years ago we did the CFD based on optimising for sub 10deg yaw as that is what modelling had identified as most useful.
Of course, all the marketing you’ve been seeing for years has focussed on high yaw. So a brand coming out with data to the contrary looks like it’s revolutionary.
But the differences among most frames/wheels at low yaw are pretty small. And the differences at high yaw can be pretty big. A pretty big difference 5% of the time, can still be a pretty big difference.
Some sorted of weighted average over yaw would be useful (using various assumptions).
Case in point are disc wheels. They don’t really start winning vs. other other aero wheels until around 5-10 degrees or so. Yet this forum would consider it anathema to ever not use a disc. And you constantly read people talking about feeling the “negative drag.” Which just happens to only occur at very high yaw.
So comparing frames out to 15 degrees or so is still pretty valid. Even if you only see that 15 degrees for one 10 minute leg of your race, why would you give that up? (Assuming the frame performs nearly equivalently everywhere else.)
Case in point are disc wheels. They don’t really start winning vs. other wheels until around 5 degrees or so. Yet this forum would consider it anathema to ever not use a disc.
Discs win on power to rotate at any yaw, so they are always fastest. It’s just that we don’t often see info on power to rotate.
In all the analysis I’ve ever done, Discs are always fastest on translational drag too - sometimes not by much - 30s in a low wind Ironman up to 90s in high wind. But it’s measurable.
Discs win on power to rotate at any yaw,
True, but I think the argument for discs exists without even considering that.
This isn’t anything new, 0-10 is where it’s at.
http://engineerstalk.mavic.com/...kona-ironman-course/
Interesting that there is so much more yaw on the return from Hawi, which is where the speed is the highest. Shows how hard that wind hits the return side of the highway.
This is certainly a stronger argument for disc brakes.
huh? how?
huh? how?
Troll…and poor one, at that.
indeed, i’d have thought the opposite was the case. as time < 5 yaw goes up, the penalty for having a bunch of stupid braking hardware out in the wind increases.
indeed, i’d have thought the opposite was the case. as time < 5 yaw goes up, the penalty for having a bunch of stupid braking hardware out in the wind increases.
Especially considering a rim IS a disc braking surface :-/
huh? how?
Troll…and poor one, at that.
Not a troll.
IIRC, disc brake aero penalty is minimal at low yaw.
Having done a little measurement myself, I concluded that cyclists rarely see more than 5° yaw.
http://skippykitten.tumblr.com/post/127802618308/normalised-yaw-distribution-from-the-test-runs
Yeah, I do not really get it. At Hawaii 70.3 last year, on the last 5.3 miles of the climb up to Hawi, I averaged 15.4 mph. On the way down that same section I averaged 35.7 mph. There is nothing to slow the wind down between the south bound side of the highway and the north bound. And since you go down right after you go up, there is not a bunch of time for the wind to increase. Yet in that data, as soon as he turns around to descend, yaw jumps from -15 to 25 (with a short section of 0 near the turnaround where there is tree protection). I would think there would need to be a very sudden and very dramatic increase in wind speed at just the right time to make this happen.
Question, when they say YAW do they mean “Pure YAW” or some sort of relative YAW influence (say in relation to pace, gravity, grade etc)?
Honest question, I really don’t know.
Maurice
Having done a little measurement myself, I concluded that cyclists rarely see more than 5° yaw.
http://skippykitten.tumblr.com/...n-from-the-test-runs
That’s very different than Flo’s data.
Flo seems to have made more of an attempt to generalize across conditions where you seemed to have picked your local TT conditions?
I’m not criticizing…what you did is great…just bring up the differences for discussion.