Index Categories:
Wheel Aerodynamics – Side forces and controlabilty on spoked vs. tri-spoke wheels
Wheel Selection – Windy day considerations
From:
MALIBU Jul 26, 2006, 5:25 PM
Question:
HED 3 handling in wind? I have been riding a Hed 3 spoke on the front recently (loaner from a friend). I ride a disk on the rear and have been experimenting with different front wheels. I am looking to buy a new front wheel since I just upgraded to 700c.
I have noticed the 3 spoke is a handful to control in windier conditions. I am looking for a front wheel and don't want to have two separate wheels for windy/non windy days. So my question is how do the new deep wheels like the zipp 808, Hed stinger 90 and Blackwell 100 ride in windy conditions as compared to a HED 3 spoke? I am about 140lbs so if they all handle similar to the Hed 3 should I just go with a zipp 404, Stinger 60, or Blackwell 50 on the front instead?
Josh:
Currently there’s a lot of discussion on 3 and 4 spoke handling being due to the way the spokes become shielded behind the fork legs in a side wind, effectively changing the surface area of the wheel depending on rotational position. The wheel is turning at a fairly high rate, so this isn't directly affecting handling, but does set up a harmonic within the system such that certain wind conditions can cause handling issues. However, I think the bigger issue is that these wheels just have a lot of surface area which leads to higher side force values for a given wind condition.
I don't have anything posted yet on the harmonic issue, but we do have info on the surface area/crosswind issues on the tech sction of our website:
Rim Shape:
http://www.zipp.com/RimShape/tabid/103/Default.aspxat the very bottom you will see a graph of side force on the wheel during wind tunnel testing. The 808 has roughly 30-35% less side force than a 3 spoke and the 404 has less than half the side force for the same wind condition.
Rim shape has a big effect here, and the large sidewall curvatures that we use in our rims not only make them more aero but also reduce side force compared to V or U shaped rims as the airflow tends to flow around the rim instead of impinging it.