I too have had the nerve racking pleasure of playing in the draft of
large trucks.  While crossing North Dakota I encountered a head wind so
strong I could barely make 50mph.  My call for a draft vehicle was
answered by a tour bus headed to Texas.  After the driver slowed down to
let me catch up, he made a beautiful hole in the wind for me.  I asked
how closely I could follow him, he said" as close as you want to, I
wouldn't feel it if you hit me".  I found 10-15 feet to be my limit at
75mph.  That's not the scary part.  After we stopped for gas, another
truck fell in behind me and changed the airflow.  They sucked me across
North Dakota at 85mph +.  I was a nervous wreck when my driving shift
was up, But we were a H--L of a long way across the state in a heaart
beeat.  I still remember pumping my brakes at 85 mph to slow down.  At
times I was only using 1/3 of the gas pedal.  It was very interesting
and fool hearted. Oh to be young.  

Kenneth Winter
TN 
87 gl Vanagon 
> SUBJECT:
> 
> >On Sun, 8 Jun 1997 00:54:12 -0500 Norman Leong said:
> >>There was some some discussion in another forum as to whether or not the lead
> >>vehicle derived some benefit from a following vehicle in a draft, a "push" if
> >
> >according to the Nascar drivers, the lead vehicle DOES derive some benefit,
> >but not as much as the following vehicles. i'm not sure our buses are big
> >enough (or fast enough) to do any 18-wheelers any good. and besides, most
> >of them do NOT like being behind 4-wheelers for very long. imho. :)
> >
> >joel
> 
> DISCUSSION:
> 
> When two vehicles travel linearly in close proximity, a small pressure
> system is formed in the "slot" between them, creating a sort of "Venturi
> Effect." The air being forced more quickly to move between the vehicles
> creates a  mini-high pressure system, and a low pressure in front of the
> vehicles, resulting in a forward vector PULL, effectively causing both
> vehicles' forward vectors to combine, resulting in further forward thrust
> (i.e. acceleration).
> 
> But this "slot" is distinctly related to vehicle sizes, placement, and
> shapes (read: air flow patterns). There is a point where you are out of the
> slot, and simply being buffeted in "trash" air (highly disturbed whorls).
> 
> Having once been the recipient of a rear tire blowing on an 18 wheeler as
> it blew by me, I opt to avoid the questionable advantage any "slot-riding"
> might afford!
> 
> Another 2 cents!
> 
> Louise