ultyguy wrote:You ever see a sprint from overhead cam shot? Especially the likes of Greipel and Cav throw their bikes back and forth so much that any 'aero' given by the frame surely gets washed up in all that churn.
A couple of sums...
The change in yaw angle on the frame due to the rocking is something like 10degrees (back of envelope calculation... 120rpm, 20cm amplitude motion gives max sideways velocity). This is likely well below the stall point of a frame - the motion alone is not enough to cause any upset in the drag response of one frame vs another.
The unsteady effects come into play when the time period of the motion of the geometry starts to approach the time period of the flow structures going past the geometry. In other words, 20m/s bike, roughly 1m long - a blob of fluid passes the bike in 0.05s. 120rpm is 0.5s period. So, 0.1 ratio of bike to fluid. This is just on the limit where unsteady effects would begin to play a role - it's fair in this circumstance to treat the bike as being in steady flow.
Sprinting is one occasion where aero can definitely play a role - high absolute drag, big power, slight differences are the margin between winning and loosing.