just something you wont note without calipers

...or, with a wind tunnel balance...apparently ;-)

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A little bummed about the H3. Been using that in all my tts this year.

I wouldn't be...to be fair, from 0-5 degrees of yaw it's within ~1W of drag as compared to the best wheel/tire combo in the test. And, as some have pointed out, this doesn't include "power to rotate", which has also been shown to perhaps be in the H3's favor.

For fast-ish TTs, experiencing yaw >5 deg is a fairly uncommon occurrence...

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Is there data available on power to rotate for various types of wheels? Disc vs 60-80mm profile vs spoke wheel ect? I have looked, but not found any.

you need to look harder. there is some pay for data on BTR but you can find other data floating around the web, you just need patience and to open a bunch of papers and read what they did in their studies. I have no links

Thanks, good to know data is out there. Any ballpark estimate on watt differences between Disc and 60/90ish wheel?

like anything, depends on yaw and speed. if concerned, just spend some time and inform yourself or do some field testing(it's built in then)

edit: also, tire width has impact on some I have seen, so.....

https://docs.google.com/...XRAL94hu0/edit#gid=0

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Dang, there is a lot more rotational drag on a spoked wheel than I thought there would be.

So are we better off deflating partially or completely if we aren't going to ride in the next couple days at least on race tires?

I doubt it would make much of a difference...besides, latex tubes "naturally" slowly deflate anyway ;-)

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Yeah, I should get around to that latex thing...

Make sure you read and absorb THIS first: http://austintriathlonstore.blogspot.com/.../01/latex-tubes.html

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It's been three days now, where is the next instalment?

Partially on my hard drive and partially in my head :-P

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Thanks for all the great insights you provide us so regularly!

I've tried to subscribe to your blog with no success. Probably user error. But maybe I am missing something. Can it be done?

Scott

There seems to be many points of view on aerodynamic torque/"watts to spin". Here are my notes when I looked at the literature a half dozen years ago:

http://www.biketechreview.com/...-torquewatts-to-spin

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Kraig Willett
http://www.biketechreview.com - check out our reduced report pricing
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I don't know...I've never tried to subscribe to my own blog :-) I'll poke around and see if I can figure anything out.

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It's been quite a while since I looked at how you were deriving watts-to-spin from the tunnel balance data...so, I forget, does that value include the tire-roller interface losses? (i.e. rolling resistance) If so, do you remove that from the calculations?

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The graphs with the wind on / no wind comparisons could be a bit misleading because it seems to assume that wind off drag represents rotational drag. This would also imply that the flows are linearly additive, which would only be approximately true in a special set of circumstances for (near infinitely) high-Re flow (see potential flow theory).

Because of the relative speed of a wheel to to the freestream, a rotational moment calculation would be heavily skewed towards flow at the top of the wheel (https://en.wikipedia.org/wiki/Cycloid) where flow is twice the freestream, whereas near the ground, the flow is traveling with the wheel surface (zero relative velocity). Since drag isn't linear, the physical effect is not the same as the average, and the true rotational cost is likely higher.

Hey man - first wanted to say thanks for your research !

I've been sitting on the edge of my seat waiting for you to post part 2!

Waiting to pull the trigger on either the ss or turbo cottons for IMFL as soon as you've finished running the numbers.

Any hints on which one is marginally faster?

Thank you sir

FYI, TomA posted part 2 yesterday

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<We all know that light travels faster than sound. That's why certain people appear bright until you hear them speak>

i'm more amazed that he got a CdA of ~0.27 on his road bike. My TT position right now may be ~0.23...

In the "real world" it's actually going to be a bit lower since that value includes the fixture drag :-)

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