Join Date: Dec 2005
Location: Auld Blighty
Bikes: Early Cannondale tandem, '99 S&S Frezoni Audax, '65 Moulton Stowaway, '52 Claud Butler, TSR30, Brompton
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Try holding a small sheet of plywood in one hand. Stick hand outside window while driving at 50 kph. Notice how things are reasonably stable when the plywood is behind your hand. Now rotate your hand until the plywood is in front of your hand. Feel the plywood flip over, trying to remove your hand at the wrist.
The centre of pressure of a rotating wheel in a fork is in front of the steering axis (in any normal steering geometry). The fork is trying to flip through 180 degrees and it is generally quite an effort to keep in a straight line. The more area presented to a cross-wind (including normal steering corrections in windless conditions), the worse the effect.
Last edited by LWaB; 12-01-06 at 08:54 PM.