Road Cycling - A question about wheel aerodynamics.

So just through reading random articles I've gotten the strong impression that wheel aerodynamics is a far more important aspect of wheel architecture than wheel mass. But I haven't been able to find a good article on what defines an aerodynamic wheel, how their manufactured and who manufactures them etc... Can someone provide me with some links or just give a general response defining good wheel aerodynamics?

A deeper rim is typically the first sign of an aerodynamic wheel. A standard semi-aero rim is anywhere from 28-30mm (Rolf Vectors often are called semi-aero). A truly aero rim is anywhere from 40-90mm deep although 90 is only usually used on rear wheels for handling reasons.Check out www.hedcycling.com they have all sorts of aerodynamic wheels and they are compared in tests. Hed is a well renowned wheel company Lance rode them for many years.
The next tweeking one can do after a deeper rim is spokes. Whether it be a Tri-spoke or Spinergy 4 spoke wheels, these are for serious racing only(I've heard of safety issues with the Spinergys). Or you can get bladed steel/titanium spokes, they are almost flattened.
Be warned that a deeper rim will also leave you succeptable to cross winds and make controlling your bike harder. The most aerodynamic wheel is the disc wheel, it has no spokes its a disc, it is only used in time trials and track racing. Like I said check out www.hedcycling.com and look at their tests and you'll see comparisons between wheel depths and aerodynamics and typicall improvements in time.

zipp speed weaponry has some info on aerodynamics. Zipp is interesting because of the patented shape of their rims that make them aero in crosswind situations too.

Deeper rims, shorter spokes, fewer spokes - those are key ingredients to aero wheels. The rear wheel is less important because the rear drafts off the frame.

I think that all this aero stuff is nice and exspensive but you really wouldn't notice a difference unless you are planning to ride at speed for a good length of time; 20 mph roughly speaking, or if you are riding down a mountain road going from 20-40 mph. I tested my bike with a friend of mine who has the Mavic Cosmic rims and I had a pair of Open Pro's 32 spoke 3x, we both had pretty close to the same type of bike and bike weight and physical weight at that. We started by coasting down a mountain road and he ended up being about 1 minute or so ahead of me and I could not catch when we started to both rachet up the speed. So then I decide to build a semi-aero rim, a velocity aerohead rim with 32 radial lace DT 14/15/14 Revolution. And we perform the same test again on the same road begining with the rolling start. This time were we pretty close to being even and even during the time when we both began cranking for more speed. My rear wheel are 14/17/14 radial laced on the non-drive side , with 14/15/14 on the drive side. I went this route for the for a lower priced aero type rim, and also so that I would experience building my own set of wheels. Oh yeah, the hubs were Ultegras.

this is common knowledge (I think), but I've read many times that a rim must be at least 40mm deep to achieve any aero advantage.

I have read that aero wheels only have an effect at speeds over 20 mph and the effect is not that great. I think it works out to about 15 seconds on an hour time trial at about 25 mph. Now, if you are doing hour time trials at 25 mph, 15 seconds is pretty significant and aerowheels are pretty essential equipment. But otherwise they really are not that important.

Well, this isn't really something I feel I need to purchase. More than anything I just wanted the knowledge, in the future it might be something that interests me because I do a mountain run every weekend that probably includes downhill sections around if not in excess of 40mph. Thanks for all the info though :)

Hed cycles claim that aero advantages from wheels end once you are slower than 14mph, which is most common on hills. Aero wheel advantages start before 40mm I believe it just isn't that significant. A 40 mm rim saves approxiamately 1 minute in a 25 mile ride(this is if you ride it in close to an hour).

I did a lot or research into wheels recently. My basic conclusion was that any aerodynamic advantage provided by deep section rims ( 40mm+ ) is offset for the average rider on a budget by their adverse characteristics in crosswinds, their cost, and their extra rotational weight in the worst possible place. In the end, I went with Tune hubs, bladed spokes in front, a regular x3 rear, and the lightest quality rims I could find - the new DT RR1.1's.

If I thought it was worth it, I'd look at the Zipp rims, but as it stands, it's hard to justify the fact that they're five times the price of a good, regular Aluminium rim. As for descending, hey, I'm a 90kg mountainbiker. No roadie descends better than I do, regardless of how aero their rims may appear to be ;)

...A 40 mm rim saves approxiamately 1 minute in a 25 mile ride(this is if you ride it in close to an hour).
One minute at 25 miles per hour is 0.42 miles. I would say that is significant.

Go 36 spoke, square section, cromed, steel! Wooo yeaa, only 1400g for the complete front wheel AND extra shiny! :)


.... As for descending, hey, I'm a 90kg mountainbiker. No roadie descends better than I do, regardless of how aero their rims may appear to be ;)
The cheapest way to decend faster is to tie any large rock to you or the bike at the top of the hill. Tain't nothin' like the potential energy stored in massive objects at high elevations.