garygid wrote:Yes, the closely-following vehicle (usually too close to do safely on the public highway) essentially streamlines the leading vehicle, by filling in the "suction" area that occurs behind most "solo" vehicles.
With a large truck, the "suction" zone is a lot bigger, but to take maximum advantage of it, one might still need to follow dangerously close.
When following the truck a bit further back, the truck can still provide some wind-braking benefit to the following car, but the truck is less likely to experience any significant benefit.
Interestingly, using the mpg gauges in a Prius and Accord Hybrid and Civic Hybrid (assuming they are reasonably accurate), I've found that the long flatbed trailers provide a better increase to my mileage than the large box trailers, when following at about 1 second behind the truck which is close, but not too close. I was quite surprised by this result, and I have tried repeating this test several times in each of the cars, and it always seems to favor following an empty flatbed trailer.