Cruising down the highway, most of an engine’s work is spent pushing air out of the way. Common sense tells us that depends on 1) how much air is in the way: the frontal area A, scaled down by 2) how slippery the car’s shape is, Cd. That’s why Cd is called the drag coefficient – it’s Cd times A, the drag area, that counts. Production cars cover the full range from sublime (2000 Honda Insight, with a CdA of 5.1 square feet) to ridiculous (2003 Hummer H2, 26.5 sq. ft.)
The first-generation Honda Insight has the lowest drag area of any mass-produced car to date: 5.1 sq. ft., the product of its superb 0.25 Cd and its svelte frontal area of 20.4 sq. ft. Too bad they quit making them. (What’s with the windmills, anyway? It runs on gasoline.)
Honda’s 1990 CRX Si achieved an excellent 5.71 sq. ft. drag area, with 0.29 Cd. Too bad they don’t make these any more either.
In spite of a little more style and a little less work in the wind tunnel, sports cars in general have low drag since their frontal area is small. This 1990 Mazda RX-7 scores a low 5.95 in spite of its 0.33 Cd.
Even the muscular sports cars do very well, like this ’92 Corvette. Today’s 430 hp Corvette delivers 26 mpg highway (EPA). Low drag area makes that possible.
With frontal area enough for a comfortable four-adult cabin, the 2nd-generation Prius scores low drag with an excellent 0.26 Cd. Today’s 3rd-gen Prius Cd is a tick better at 0.25, but it’s a little bigger too. Note how the Corvette and the Prius have nearly identical drag areas. A Prius is bigger than a Corvette but it has a better Cd.
OK, enough with the hybrids and sports cars, how about a normal family sedan? Chevy did well with the 2nd-gen Lumina, Cd 0.34 and drag area 6.96.
Ford’s classic big American rear-drive V-8 sedan develops 8.7 square feet of drag area, with a 0.33 Cd taking the edge off all that space.
With a chunky Cd of 0.42 and beefy size, the archetypal SUV must deal with 11.7 square feet of drag area.
The H2 was seemingly an exercise in how monstrous a four-passenger conveyance could get. A drag coefficient of 0.57 compounds its hugeness, presenting a drag area of 26.5 square feet. Five Honda Insights push less air aside than one Hummer H2. Here’s hoping we never see its like again.