Aero Wheel - How Deep?

chris_gr said:

Is there a lot of advantage going from a 21 spoke, 30mm "mid" deep rim (Campy Scirocco), to an all out race wheel like the Zipp 404? Main use is Tri/TT (typically in the 35-40kph range)?

Studies have shown that not much aero advantage is actually gained until wheels are 40mm in section. IOW, 30 mm deep rims just "look" faster.

And deep section rims are not advantageous in anything but dead calm or direct headwind.

Weisse Luft said:

And deep section rims are not advantageous in anything but dead calm or direct headwind.

Good you mentioned that. I've read that as the "apparent wind" direction goes to 15 deg or higher off-center, aero wheels have more drag, not less.

So, at 25 mph, if you had to fight a 8-10 mph crosswind, you'd actually be worse off with an aero-section rim.

Does anybody have any links to any of these studies? it sounds interesting.

chris_gr said:

Is there a lot of advantage going from a 21 spoke, 30mm "mid" deep rim (Campy Scirocco), to an all out race wheel like the Zipp 404? Main use is Tri/TT (typically in the 35-40kph range)?

I was reading a report the other day where a fella from melbourne and a fella from I think it was England had tested wheels in real life conditions. They both found that campag shamals were the best overall due to their height not being effected too much by wind, a deeper rim would still be faster but theres the control issue. If I can remember right a shamal is about 40mm deep. Bit heavy so would be alright for time tiral or triathlon but might want something lighter on the track or road. Corima, Reynolds, Zipp, X-treme all make light carbon ones but are expensive. Basically make sure its as close to 40mm as possible for windy days, deeper the better for non windy days, and lighter the better for technical courses.

Another factor is stiffness, no use being aero if youve got no power going through. This might be interesting to some of you: http://www.sheldonbrown.com/rinard/wheel/data.htm
a bit old but an intersting point for me was the stiffness of ksyriums that everyone raves on about, apparently not so.

If I can find the study with the shamals in it i'll post it. For chris_gr it all depends on how serious you are a scirocco will be fine for racing but if you want to get every second you can out of you wheels go for carbon tubulars, although shamals are good alrounders on a nice day you'd be better off with zipp or reynolds. Good luck.

sheldonbrown.comdata.htmOpen ↗
a bit old but an intersting point for me was the stiffness of ksyriums that everyone raves on about, apparently not so.
QUOTE]

They are measuring lateral deflection, in other words side loading, which isn't really applicable to actual use or indicative of stiffness in the directions that matter. Rims and wheels are designed to receive and transmit loads at the outside and inside of the rim along with torsional loads from pedaling. Their data doesn't give any data on these points.

chris_gr said:

Is there a lot of advantage going from a 21 spoke, 30mm "mid" deep rim (Campy Scirocco), to an all out race wheel like the Zipp 404? Main use is Tri/TT (typically in the 35-40kph range)?

And yes, there is an advantage. Whether it's "a lot" depends on your definition of "a lot" and the size of your wallet. If you're racing in a situation where a few seconds is the difference between winning or not, then every wind cheat you can find helps.

hwttdz said:

Does anybody have any links to any of these studies? it sounds interesting.

http://www.bsn.com/cycling/WheelAerodynamics.html

The "Vendor Data" table at the bottom of the page shows drag data for various yaw wind conditions. EG, if you look at the Shamal vs Am Classic Low Profile, you note the Shamal drag starts lower, but goes higher as the crosswind angle increases. Hope I'm reading this right.....

dhk said:

http://www.bsn.com/cycling/WheelAerodynamics.html

The "Vendor Data" table at the bottom of the page shows drag data for various yaw wind conditions. EG, if you look at the Shamal vs Am Classic Low Profile, you note the Shamal drag starts lower, but goes higher as the crosswind angle increases. Hope I'm reading this right.....

If that tri/TT is in Hawaii, hmm, maybe not. It's so windy at the Ironman that I heard disk wheels are banned. I dunno if even Z404s would be helpful in those gusts.

If it's light/no wind, then I'm sure it helps. And no doubt... it looks very cool!!

dhk said:

http://www.bsn.com/cycling/WheelAerodynamics.html

The "Vendor Data" table at the bottom of the page shows drag data for various yaw wind conditions. EG, if you look at the Shamal vs Am Classic Low Profile, you note the Shamal drag starts lower, but goes higher as the crosswind angle increases. Hope I'm reading this right.....

Yep you're reading it right. Thats where the handling thing comes in, wind from the side makes deep wheels act like a wind sock. The low pro is good in cross winds because its an absolute midget height wise. You will however notice that the drag readings front on are much higher on these wheels than the shamals. Overall the shamal is the best wheel as it has the best balance, and most importantly a good 0 degree reading for still conditions. It's an allrounder whereas youre american classic's are just good in crosswinds.

thedivekrb said:

sheldonbrown.comdata.htmOpen ↗
a bit old but an intersting point for me was the stiffness of ksyriums that everyone raves on about, apparently not so.
QUOTE]

They are measuring lateral deflection, in other words side loading, which isn't really applicable to actual use or indicative of stiffness in the directions that matter. Rims and wheels are designed to receive and transmit loads at the outside and inside of the rim along with torsional loads from pedaling. Their data doesn't give any data on these points.

Every direction matters. If your bikes laterally moving one way and your wheels going the other way theress no doubt thst you're losing power. For a weird example lossen your cones right off and then see how that affects your performance; it's feels awful. On a larger scale its like going round a downhill corner flat out with 20 psi in your tires. The lateral movement affects performance. To be really picky if your wheel is moving 2 mm under a 10 kg load it will move more under real life conditions, resulting in a portion of the back wheel being directly exposed to the wind and hence creating more drag. Both ways youre going to be slower.