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PostPosted: Sun Aug 04, 2013 7:02 am 
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I just commented in the Flo 30 thread and it got me thinking - why do people choose the rim depth that select for thier Al clinchers?

Trade off between weight and stiffness? Aero vs weight? Appearance? Number of spokes you can use?

When I next build up a set of rims I'll be looking at the Pacenti's - decent moderate weight, stiff, and a little aero. Really want to try some wide rims (widest I've used is campy rims which I think were 21/22mm wide)

Most popular rim depths (in custom wheels) seems to be 24-28mm - but what is the motivation behind that? I'm hoping some of the wheel builders offer an insight.

Most of the big name prebuilt clincher wheels tend to target lighter lower profile rims (Shimano, Campy, Mavic)- but then they are targeting OEM sales and hence light weight sells on the show room.


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Posted: Sun Aug 04, 2013 7:02 am 


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PostPosted: Sun Aug 04, 2013 4:28 pm 
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Over 32mm or so, alu is almost always heavier than carbon. Under 24mm or so, rims tend not to be as stiff, so higher spoke counts (i.e. more weight) become necessary.

In the 24-32mm range you can build something that's fairly light, and/or fairly strong, and/or fairly cheap. (Pick 2.) You can even have a bit of aero, although the differences are relatively trivial for the most part.

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PostPosted: Sun Aug 04, 2013 4:32 pm 
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That's the depth range you need for good aero performance (along with a rounded shape) and depth also influences lateral stiffness quite a bit.

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PostPosted: Sun Aug 04, 2013 4:33 pm 
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MajorMantra wrote:
You can even have a bit of aero, although the differences are relatively trivial for the most part.


Not trivial... unless you think Zipp 808s are also trivial.

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PostPosted: Sun Aug 04, 2013 4:50 pm 
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I said in "in the 24-32mm range". I meant the aero advantage of 24-32mm rims is relatively trivial compared to traditional low profile rims. Admittedly that may not apply to rims like the Flo or the Zipp 101 but for the most part you aren't going to see significant aero gains without going quite a bit deeper.

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PostPosted: Sun Aug 04, 2013 5:47 pm 
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what about Kinlin xr380---higher but awsome rim. fast stiff nice looking

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PostPosted: Sun Aug 04, 2013 6:26 pm 
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It's not light though - 550g.

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PostPosted: Sun Aug 04, 2013 7:25 pm 
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The XR380 is a pig of a rim. I think that in the real world the XC279 is far more versatile (and dare I say aero) rim, especially with the crosswinds.

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PostPosted: Mon Aug 05, 2013 12:04 am 
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MajorMantra wrote:
I meant the aero advantage of 24-32mm rims is relatively trivial compared to traditional low profile rims.


Not true at all. Have you looked at the data? Something like a Pacenti or XC279 would be closer to the 808 than a "traditional low profile rim". If you also use round spokes the difference is huge.

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PostPosted: Mon Aug 05, 2013 12:58 am 
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WMW wrote:
MajorMantra wrote:
I meant the aero advantage of 24-32mm rims is relatively trivial compared to traditional low profile rims.


Not true at all. Have you looked at the data? Something like a Pacenti or XC279 would be closer to the 808 than a "traditional low profile rim". If you also use round spokes the difference is huge.


Please provide references. The only data I have seen backs up the assertion that these rims aren't anywhere near the aero performance of a Zipp 404, not to mention an 808.

I have also only ever heard that rounded vs bladed spoke differences are minute. But I am most recently thinking of the wind tunnel testing that November did. AFAIR, that is why they decided to use round on their 30mm alloy wheels.


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PostPosted: Mon Aug 05, 2013 1:19 am 
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The number of spokes has a much bigger effect on aerodynamics than the shape of the spokes IMHO. The XC279s feel 'aero', but this could be due to lower rolling resistance or comfort due to tire shape, or both.

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PostPosted: Mon Aug 05, 2013 10:40 am 
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pushstart wrote:
Please provide references.


+1.

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PostPosted: Sat Aug 10, 2013 5:22 am 
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pushstart wrote:
Please provide references. The only data I have seen backs up the assertion that these rims aren't anywhere near the aero performance of a Zipp 404, not to mention an 808.


Then please provide references for *your* data.

I said they were closer to an 808 than a shallow rim with lots of round spokes.

I have a large collection of wheel wind tunnel tests that prove the point. Not seeing that I can upload files here though. Tour has one of their QTRs online however, and you can see a good cross section of different wheels there. Note particularly:

Komponentix All-Weather, shallow rim, 28 round spokes 47.1W.
Corima Winium+, rounded 22.5Wx23.3D rim, 18 aero spokes, 27.2W
Zipp 808, 19.5W

This is typical.

http://www.tour-magazin.de/services/qtr ... page3.html

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PostPosted: Sat Aug 10, 2013 11:16 am 
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SO what I'm trying to pick out of this.....

-A rim over 500grams is starting to be considered too heavy no matter what the profile.
-Either side of 450grams typically gives a good trade off of properties
-Nobody is ever going to agree that a sub 35mm rim is really "aero", just that it is a bit more aero than a set of 32 spoke open pros....


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Posted: Sat Aug 10, 2013 11:16 am 


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PostPosted: Sat Aug 10, 2013 2:53 pm 
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Even a 25mm rim can be quite aero, if it's wide and rounded. The place where the *good* deep rims see the biggest advantage is at high yaw... which is precisely where most riders start wishing they weren't on deep rims anymore!

If you are serious about TTs then deep rims make sense. If you are serious about road racing then carbon tubulars are the ultimate. But most riders buy deep carbon rims for style. Nothing wrong with that, but the speed gains (if any) over a good aluminum rim like the SL23 or XC279 are trivial.

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