What contributes most to the benefit of aero wheels? Deep section rims or reduced spoke count? I have a nice set of 28 hole hubs at the house. Would it be beneficial to build them up to some deep section rims, or would I just be wasting time due to the ‘high’ spoke count?
air resistance is what makes an aero wheel aero 
.
Can’t find the article at the moment. but read somewhere that deep dish is more significant than spoke count or spoke shape. The spokes aren’t insignificant, but the article claimed that the dish depth was more important.
Great info on Zipp website…
Actually, isn’t lack of air resistance what makes an aero wheel aero? 
no. it’s air resistance.
an aero wheel is aero compared to an non-aero wheel…remove the air (and therefore air resistance) and then there is no need to talk about aero wheels, as there is no air resistance anymore
My brain hurts from trying to understand that.
In order of importance the factors we look at are: 1. Rim Depth 2. Rim shape 3. Spoke shape 4. Spoke count
The rim depth has the double effect of both providing surface area for the wind to move over and hopefully reduce flow separation (control of the airflow essentially) and the deep rim shortens the spokes. Since the top of the wheel is traveling at twice the speed of the bike, the less deep the rim, the faster the outer portion of spokes is travelling, hence more drag.
Rim shape can be used to blend the tire shape and prevent flow separation at various wind angles. Certain rim shapes, mainly ‘V’ shaped rims perform mainly as spoke shortening devices as only with very narrow tires and at a few wind angles will the airflow remain attached to the rim. So most of the time, the rim is drafting in the turbulent wake of the tire. Tweaking rim shape can have major benefits, look at the link pasted from our website above http://www.zipp.com/tech/documents/ANoteonRimWidth_002.pdf and you see that just chaning our rim shape has allowed us to nearly cut drag of the 404 wheel by half over the last 5 years, and the new 38mm deep rims are faster than the original 58mm deep ‘V’ shaped Zipp 440 rims, so you have 0.2 lb less drag (about 8 watts savings) just in rim shape.
Spoke shape, this can be huge, check out the Note on Spoke shape on our website, and you will see that round spokes vs. oval on the same wheel can cost as much as 10 watts!!. You want oval or bladed spokes, and butted/ovalized spokes seem to be the fastest with best combination of shape and frontal area.
Spoke count, this is the one thing that everybody gets anal about, but really is not that big a deal. Our most common ‘custom’ wheel request from consumers is 2 or 4 spokes less than the stock wheel, and honestly, the wind tunnel does not have accurate enough resolution to really conclusively prove that 2 fewer spokes is faster (theoretically it is, I’m not disputing that, but the difference is so minimal). Cutting 10 spokes can be measurable, but still not as much as simply changing the spoke shape. Check out: http://www.zipp.com/tech/documents/Anoteonspokecount_000.pdf
Lastly, tire choice will affect wheel aerodynamics. You want a tire that is equal to or slightly narrower than the aerodynamic width of the rim you have. For ‘U’ of ‘V’ shaped rims, this is the width of the brake track, for rims made under the Zipp patent, this is the width of the bulge in the sidewall. Failing to do this will negate some of the benefit of the wheel you are using, as much as 25% in some instances.