According to the reports by aerodynamic engineers, the drag coefficient (Cd) of automobiles plays a very important role in the gas efficiency of the vehicles. Most modern automobiles have a Cd of .3 while vans, SUVs and trucks have Cd of .7. What this translates to is that according to these engineers,  flat fronted vehicles such as most trucks and SUVs when running at high speed (70 MPH+) consume as much as 60% of its energy in tackling wind resistance. Big rigs normally install a streamlining devices over its cabs to reduce Cd. But their flat rear ends cause a lot of turbulence contributing to higher Cd. There is not much owners can do regarding the shape of their cars citing the Honda Element, the Scion and Humvees as examples. Remember the old Cadillac "Torpedo", its rear shaped like the trailing edge of an airplane? But to sacrfice the trunk space will never fly. Anyone know of a device that breaks up rear turbulence when traveling at high speeds? Racing cars do.

Bubblehead

If you take a close look at a modern F1 car, you'll see they have many small little wings attached to various parts of the car, from the engine cooling inlet all the way to the rear wing itself. Thats the sort of thing that would reduce it. Nothing like that would work though on a road car. They are designed to either be as efficient as possible or as stylish as possible.

Do we really want those massive machines around all those vulnerable children and pedestrians? I only see one advantage, when they do run over someone, their car won't be damaged... 

I don't have an SUV. My wife drives an Acura 3.2TL and I drive a Ford Ranger P/U with a cab. The subject on rear end turbulence which create a drag on the vehicle most notably in high flat rear ended models, if there is a way to reduce that, it sure will make a difference in the gas mileage. That's why you see NASCAR racers tail gating one another to reduce fuel consumption. I'm going on a thousand mile trip next month and with the price of gas nowadays, I'd like to experiment fuel conserving. First of, I'd lower my speed to the posted  limit 65-70 MPH.  Make sure my tire pressure is up and I'll use cruise control whenever possible. with a Lear cab, my rear end is a flat surface resulting in back turbulence during high speed. I'll lift the back window open about 45 degrees which reduce the low pressure bubble substantially, I think. You think it will make a difference? It should on the basis that aircraft and racing automobiles have small trailing edges.

Bubblehead

FYI:

Got this from aerodynamic engineers in their website:

Total Load = A + B x v(to the second power) + C x v(to the third power) where,

A (constant) is the vehicle weight.
B (varies with RPM) is from friction.
C (constant) is the drag coefficient

v (variable) is the velocity

Considering that at the lower speed you will be driving twice as long, if you increase your driving speed from 35MPH to 70MPH, your load factor increases five (5) times. According to the eningeers the most economical speed is between 40 & 60 MPH and the most inefficient is 0MPH (idling).


Bubblehead

my car has a drag coefficent of .379 

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lol, i dont understand "B (varies with RPM) is from friction." how is this represented, Speed? Gets kinda confusing when you dont take into account specicfically all drag factors, or limitations.