I was hoping this was about swimming.

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http://adamfort.blogspot.ca/

Certainly there will be more drag with nipples exposed, but you may have a hard time measuring it.

and if you have tubulars especially, you will hate life eventually if they are hidden.

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

I would recommend taping the nipples to reduce drag............for swimming that is!!!

I thought this was a cross dressing thread

so disappointed

What BrianB said

OP should be banned for disappointing thread...

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The entire event (IM) is like "death by 1000 cuts" and the best race is minimizing all those cuts and losing less blood than the other guy. - Dev

I don't have any data but I'll gladly tradeoff the relatively small aerodynamic drag benefit for the ability to touch up a wheel without having to remove the tires. As Jack said, on tubulars that's just nuts and I have owned (past tense) wheels like that.

The big question is, can ya milk 'em?

I've looked at this at least a dozen times over the years in the tunnel. Theoretically, it has to be worth something, but it's really hard to quantify. We've seen +3 to -10 grams of drag comparing hidden nipple wheels to identical exposed wheels, but if you overlay dozens of runs, you find that they are as often as not, equal. Taking an average, the hidden are likely a few grams lower drag, but with the best tunnels having precision of 9-10 grams, you just can't really say that one variant is 4 grams lower drag..maybe the marketing guys can say that, but not the engineers ;-)

For a reference data point, we got to the point that we could tell from the data which mold a GP4000s came from depending on the left/right yaw distribution as none of them are perfectly symmetric. Tires from one mold could have stall point changed by 2.5-5 degrees yielding 20+ gram differences at certain yaw angles..but really nowhere have I ever seen data that could blindly be looked at and said 'that's hidden, that's exposed' which is the true test!

When we first implemented CFD at Zipp that was one of the first major projects with Matt Godo, we build a modular modelling system that could insert or remove nipples only remeshing that zone, and then ran full transient simulations looking at the combination of translation and rotational drag. The results from our first test (over 20 Tb of transient runs!) was a prediction of 8.9gm additional drag with nipples.

Similar story is true about fairing wheels, common sense says that the oversized holes in the fairings where the spokes enter cost drag..and CFD shows that this is almost certainly true. However, since nobody makes an identical wheel that is structural in one instance and not structural in the other the only test is to clay over the holes..and I've found that the imperfections of the clay or tape used to clean up the holes must offset any 'gain' in performance (or maybe just doesn't make any difference..) no good way to test, but in practice, I could show you both sets of data and you couldn't tell the difference.

Josh

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http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
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Take a short break from ST and read my blog:
http://tri-banter.blogspot.com/

yeses just glad SOMEONE got it

I have nipples, can you milk me?

Gentlemen, we can milk him. We have the technology.

Mind blown

it gets exponentially harder if the nipples are hidden though.
just sayin....

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I reject your reality and substitute my own!
Adam Savage

Thanks Josh for this awsome answer !

I knew it was hard to see "something" in the tunnel on the subject but I was wondering about CFD so glad to see you tried that too !

Basically for clincher wheels, I think there is no reason not to go with internal nipples... tubular wheels used by pro teams I can understand that correcting the lateral trueness slightly without having to dismount the tubular is a bit time saver (though I wouldn't do anything but a very slight correction without removing tubular and glue on a wheel), but with clincher it is so quick to remove tire/tube/rim tape and it makes for such a more precise correction (possible to check both lateral and vertical runouts) that I don't see a reason to make a clincher wheelset with external nipples. There is a good chance it will always be a very small advantage to use hidden nipples and it's not a hassle on a clincher wheel IMHO so worth it every time for me... plus it looks cooler ;-)