More On Wheel Profiles and Wind--Does Body Weight Matter?

posted Mar 26, 2010, 7:59 AM by Donald Vescio   [ updated Sep 12, 2011, 8:11 AM ]

In my testing and research, I haven’t found rider weight to be a determining factor—Elaine, who might weight all of 105 pounds, runs a disc in back and either a 90mm wheel or Hed3 in front.    Given that she’s using 650c wheels, her front wheels actually have more surface than mine.  It’s all about playing with the center of pressure and working on handling.  Me, I haven’t used a rim shallower than 100mm for the past three years or so, regardless of the wind. 

Your question about composite spoke wheels is excellent!   A deep profile rim has no discontinuities, so regardless the rim is essentially fixed in relationship to lateral forces.   A trispoke or quadspoke wheel (I’ve done some long TTs in the wind with my Mavic IO, which has five spokes!), *has* discontinuities, which means lateral forces can vary considerably, depending on the position of the spokes during the wheel’s rotation (remember, in a deep profile rim, wire spokes have minimal cross sections and generally are evenly distributed).   This makes a trispoke more challenging to handle in gusty winds because most riders have difficulty moderating their steering corrections when hit by a transient wind gust—depending on the position of the spokes, corrections needed might be large or small. 

Hed 3 -- still one of the fastest all-purpose wheels available.

A lot is practice (try riding around a large parking lot, for instance).   If you’re running a disc in back, the 808 should be manageable, even in very high wind conditions; it also will have the advantage of stalling a bit later a higher yaw angles.  If you’re running an 808 front *and* rear, then  you will be more susceptible to transient gusts. This is one reason why companies like Zipp pair an 808(f) with a 1080(r), and Hed a Jet 6(f)  with  Jet 9(r).  

The biggest benefit of a well-designed composite spoke wheel like the Hed3 is that drag can decrease as yaw increases—they won’t stall above a specific yaw angle like deep profile rims will (when a wheel stalls, it loses its aerodynamic advantages).  The Hed3 is a decent performer at low yaw angles; it’s the best performer at high yaw angles.  At very low yaw angles, frontal profile is more important than cross section—the fastest front wheel that I’ve ever used at 0 to 2 degrees of yaw (which is reasonable angles for a very fast ride) is an old Campy Shamal, which has a relatively shallow profile.

Campy Shamal--still one of the fastest low-yaw
wheels out there.  This wheel is circa vintage
1997 or so.