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RE: Question about drafting
my hypothesis would be the decrease in the forward vehicle's gas mileage is much outweighed by the increase in the following vehicle's mileage
No increase in aero drag for the leading vehicle, therefore, no fuel mileage decrease. In fact, the tractor-trailer rig in this scenario would get IMPROVED mileage.
The nasty air BEHIND a given vehicle is the hardest to handle elegantly for low-drag, but it's where most of the gains can be made. This is why the drafted tractor-trailer's mileage would improve (but not by as much as it would if being followed by another T-T rig).
Cleaning up the trailing airstream is aerodynamically desirable but driving a car with a long, pointy tail is not going to happen, is it? So, they do the best they can. Look at the Honda Insight's tail. The rear-fenders pinch-in rather severely for a street car, and that's part of the magic.
Also look at the older Citroen DS series. The DSs were much-admired for their aerodynamic qualities and the Insight is, roughly, a large version of the same concept. Basically, it's like a teardrop with a truncated tail.
Geronimo
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RE: Question about drafting
When young and foolish I practiced drafting behind tractor trailers while on long haul interstate drives. I noticed that the benefits in terms of how much I had to hold down the throttle were quite noticeable as I approached the trailer's rear bumper to about 10 feet (very dangerous!). The airstream is rough and there is tremendous buffetting at that distance but you seem to be riding in the pocket of air turbulence just behind the trailer. My impression was that I had no noticeable effect on the semis and my hypothesis would be the decrease in the forward vehicle's gas mileage is much outweighed by the increase in the following vehicle's mileage. I'm too old to try to get the direct data with my car's OBDII data computer hookup (wife and son would kill me), so does anyone have solid data on that?
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