QUOTE (R. iMTY @ Dec 2 2008, 07:01 PM)

'slip stream' ?? whats that then

Some drivers have been known to draft behind other vehicles, particularly tailgating larger vehicles, to save fuel. For example, hypermilers using this technique can achieve 75 mpg or more . Some sources say that the most common tailgating does not save gasoline even at freeway speeds because one is likely to accelerate and brake so frequently that any aerodynamic savings are lost through the brakes . On the show Mythbusters, drafting behind an 18-wheeler truck was tested and results showed that traveling 100 feet (30 m) behind the truck increased overall mpg efficiency by 11%. Traveling 10 feet (3.0 m) behind the truck produced a 39% gain in efficiency. Of course, they warn that this type of driving "is insane" because the truck's blindspot is in that area, and if the truck stops quickly there is much less time to react .However, since trucks simply cannot stop quickly because of their mass it is much safer (and more efficient) to draft behind a large truck than it is to draft behind a car or van.
formula one and most racing cars do it no to save fuel but to gain a few extra mph to overtake the car in front on a long straight.