# Aero rim advantage?

Discussion in 'Cycling Equipment' started by herbert.nrp, Mar 3, 2004.

1. ### herbert.nrp New Member

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I am interested to know if anybody is aware of data regarding the difference in aerodynamic drag between spoked wheels with different rim sections. For example, what would be the difference between the drag coefficients for otherwise identical wheels if one had a rim section of, say, 24mm and the other had a rim section of, say 34mm? Of course, the wheels are not likely to be identical, because the wheel with the thicker rim may also have fewer spokes.

I have seen data comparing the drag coefficients of spoked wheels and aero disc or three-spoked wheels (for example, at Analytic Cycling, www.analyticcycling.com), but never comparing spoked wheels with different rim sections.

Thank you for your responses.

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2. ### shokhead1 New Member

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I wouldnt worry about it unless you ride at 20 mph or more most the time.

3. ### marlon1 New Member

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20mph isn't that fast is it...!!!

Here is the difference in Power, so you can compare it with a hometrainer with power measurement

Power drag= 0.5*Cw*A*p*v^3

Cw= constant number mostly bewtween 0.1 and 1. It tells how the thing is shaped. A flat Rim has Cw=1 and a aero rim 50mm: Cw=0.4

A=frontal aera in meters. This stays the same. You can take:
213/3.1215 cm* 2.3cm

p=thickness of the air. Take 1.2 minus 0.1 each 1km altitude

v= you speed in km/h

You fill it in for both and you see what the power difference is.

For 42km/h it is about 10watt.

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Now I don't calculate the extra force needed to rotate the deeper rim. But that is is not much.

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5. ### murky New Member

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Check out the ZIPP website.

http://www.zipp.com/TechInfo/wheel_rim_discussions/index.html

They have discovered/published some interesting things about rim depth.

Besides, it's a good read.

6. ### marlon1 New Member

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ok...

speed of the rim = 2.13* normal speed.

the frontal area stays the same. Because seen from the front the deep rim is behind the tubular.

Now I can say the I hav less wind resistance with a deeper rim, becuase my spokes are shorter, and the mean speed of the spokes thru air is less (the outside of the wheels is rotating the fastest)

And I can say a deeper rim has some more wind resistance because the of the extra surface.

etc.
etc.

so only looking at shapes of the rim + tubular.

I think the difference is more. That 30sec. is for a Disk.

If you think it will make you faster (and it is... how much is an other question), you will always cycle faster!