Dan Resler wrote:
....If I place a standard legal-size envelope at
> the back of the seat, it will fall off the front after 18-20 miles of
> Interstate driving. And this will happen with just about anything
> relatively light.
>
> But why? ....

Check the angle of the velour fibers.  They are pointed toward the front
of the seat.  Any vibration will move the object in the direction of
these fibers, for as they go up and down they push the envelope ever so
slightly forward each time.
--
Regards,
David Bogle
Brooklyn
'87 Syncro Westfalia