Yes, it can be done safely at higher speeds because the draft zone grows
rapidly with increasing speed. I used to enjoy drafting on my bicycle when I
was young and studly (don't laugh!) - at 40 mph the draft extended far
enough from even passenger cars to be felt at a safe following distance. On
a bicycle it feels like a warm and quieter area, because the wind speed
drops considerably. Down hills at 35 mph or more the effect is so strong
that it makes the difference between having to pedal to keep up and having
to touch the brakes to keep from running up on the car ahead.

However, even a slight sidewind will push the draft way off to one side.
Pity.

Last I heard, the speed record for a bicycle drafting a car was something
like 154 mph! Needless to say, that was not at a safe following distance.

Mike

Motorcycle riders use this technique all the time, not to save gas, but
to ride comfortably behind a large truck. I did many times when I owned
a bike.
But if the truck wood hit the break for some reason, for animal etc..
you certainly become pancake. (o:
JS

Is your average MPG from the display or calculated when you
actually fill up the tank?