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PostPosted: Mon May 10, 2004 3:56 am 

Joined: Thu Apr 15, 2004 12:00 am
Posts: 29
I put up a request for busted rims in the Wanted forum but I have not had any replies. I am intersested in conducting a CFD analysis of rim sections to determine the profile with the least drag and side force. To do this analysis I need to know the exact cross section of the rim. I think this data would be of great interest to the group since there seems to be a lot of interest in different wheel designs.

I was hoping someone had busted rims or knew someone that did so I could obtain sections and measure them. I have tried the manufacturers but they are not interested. If anyone can help please let me know.

Possibly we could try photographs with some kind of reference in the picture. The trick with photographs is getting the curved sections right. If anyone is willing to try this let me know.

Or maybe the wheel owner could carefully take measurements and forward them to me. This will take some experimenting to be sure the data is accurate.

I will post the information as it becomes available. Also, CFD stands for Computational Fluid Dynamics which is the use of powerful software and computers to model real world air flow. Thank you in advance for your help.


 Post subject:
PostPosted: Mon May 10, 2004 9:25 pm 

Joined: Thu Oct 23, 2003 5:18 pm
Posts: 742
Location: Austin
I did aero testing of actual rim samples for development of the Nimble Crosswind. We considered everything from head on 0deg to 22deg yaw. When considering rim only, no hubs or spokes, we found one undisputable fact, greater the yaw, greater the turbulence which was proportional to rim height.

This means the shorter the rim section the more aero considering you cannot guarantee head on winds.

We tested over 30 samples of rims as tall as the zipp 440(top aero dog in ’96) to the smallest box sections. We decided that shorter is better given a variety of wind on any given course. Again, considering a full spectrum of yaw, the Sun M17a was the fastest rim of that time. Interestingly enough, it was also among the lightest.

I really wish I was in possession of that data but it belongs to the company I was working for at the time.

Good luck with your testing.


 Post subject:
Posted: Mon May 10, 2004 9:25 pm 

 Post subject:
PostPosted: Tue May 11, 2004 1:50 am 

Joined: Sun Apr 11, 2004 5:21 pm
Posts: 101
Location: U.S.

Are you just looking for complete rims or can you just live with a small section sawed out of a rim? (much easier to mail to you, eh?).

Per nicrump... will you be doing CFD on the sections at various yaw angles?


 Post subject:
PostPosted: Thu May 13, 2004 11:54 am 
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Joined: Mon Sep 30, 2002 1:59 am
Posts: 1386
Location: Sydney, Australia
sounds very interesting. Do you know of anywhere I can locate data of wheel drag? The impact of spokes and hub friction is important to the complete package.
WW has some good data on tyres but not on wheels as yet.

How is the research going?


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