Aerodynamic long tail improves fuel efficiency 15 percent


December 29, 2009's Darin Cosgrove recently added this 1.37 tailpeice to his Pontiac Firefly to improve its drag coefficient from 0.34 to 0.23 and its fuel efficiency by 15.1 percent at 90 kmh (56mph).'s Darin Cosgrove recently added this 1.37 tailpeice to his Pontiac Firefly to improve its drag coefficient from 0.34 to 0.23 and its fuel efficiency by 15.1 percent at 90 kmh (56mph).

While windtunnels have long been employed in aerospace and all forms of race engineering, we’re likely to see them employed more frequently in future in the quest for improved fuel efficiency from our automobiles.’s Darin Cosgrove recently added this 1.37 tailpiece to his Pontiac Firefly to improve its drag coefficient from 0.34 to 0.23 and its fuel efficiency by 15.1 percent at 90kmh (56mph).

The 15 percent improvement is just from the tail, and was comprehensively proven with multiple bi-directional averaged runs at exactly 90kmh on a straight and level road, with no other traffic. The tail was removed and reinstalled during the test so the ‘A-B-A’ comparisons could be made in identical conditions.

The moral of the story is that it’s just as important to leave the air undisturbed as it is to slice through it effectively and one wonders just what shape our cars (and trucks) will be a few decades from now given the remarkable results of this homemade fuel extender.

Via Wired from


Good job Mr Cosgrove. So many of the cars on the road would have better aerodynamics if they were driving backwards! There oughta be a law against that...


well, compared with a current BMW 0,34 is ridiculous!

so here you can see, what is really bad ..

Facebook User

Cool -- any triathlete / time trialist that uses one of those dorky aero helmets is going to be happy to hear this.

josh kahan

I have seen this done before. The problem is now you have a 15 foot economy car. Try parking this in the city. How do you put the pac and play in the trunk? The soon to be out Chevy Volt has gotten its drag down to .28 without extreme measures like the one above:

I am sure the battle for better drag numbers will continue.... -Dennis

It almost seems like this used to be known at one time. If you look at old stream line cars from the 1920\'s and 1930\'s you will see that they almost always had a long cone shape on the back of them, was this just something we lost and are now re-discovering?


Not being rediscovered at all. The long, tapered tail was discarded as a practical design decades ago. It\'s wasted volume and material. The Kamm tail is far more practical and just as efficient. What Cosgrove did was improve a car with terrible aerodynamics. That\'s not hard.


It\'s not a battle for better drag numbers, It\'s not something we\'ve forgotten. we\'ve always known this. we just ignore it.

At speeds well below the speed of sound a teardrop, round side forward, gives the least drag. So I\'m voting with Foghorn (above) on this one:

So many of the cars on the road would have better aerodynamics if they were driving backwards!

It\'s a battle for better drag numbers while ensuring that the car looks like what we\'re used to.

yeah, it\'s 15 feet long but only because it was designed without the tail in mind. hopefully, since the price of gas is never going back down, and we\'ll start accepting cars that look like reverse hatch-backs (hatch-fronts?).

Mark Daoust

I have seen several times in past 60 years , it is nice that this is brought up from time to time.


They\'ve been working on drag since day dot. Just making it sexy is the hard part ;) Otherwise we\'d all drive artillery shells around Where\'s a force field when you need one? Then we could all drive boxes with invisible tear drops to stealth our way through the air :P

Craig Jennings

Maybe we can add something to the trunk that extends during driving like planes retract their wings for efficiency. It also acts as a bumper extender-cushion-and comes back into the trunk area when not needed.

Nick Gencarelle

How about making a retractable one that acts as a bumper extension as well-like airplane wings that retract for efficiency.

Nick Gencarelle

This would be great for those of us who carry gear like kayaks, paddles, fishing poles etc. For others, it might be better to have a telescoping tail that can be compressed when not on long trips. \" Form follows function\" still works.

Ron Wagner

A telescoping tail would be a mechanical nightmare, adding weight, cost and complexity to a car. The fact is that an extended tail is not necessary. A Toyota Prius already achieves a Cd of 0.25 without such a tail. Mercedes claims one of its recent cars gets to 0.24. Both look like normal cars, drive like normal cars, take up no additional parking or road space. With increased congestion, the last thing we want is for lots of cars to grow longer. We don\'t even know that Cosgrove\'s Cd figure is accurate. It probably isn\'t. I sincerely doubt that he put that inside a wind tunnel and did controlled tests with proper instrumentation. He\'s probably guessing, and almost certainly optimistically.


By the way, the teardrop conjecture is also incorrect. What\'s aerodynamic in a free airstream is not necessarily so when you factor in the ground, with interference drag, ground effect, etc. Look at Buckminster Fuller\'s Dymaxion car from over 75 years ago. Rounded front, long tapered back and it only achieved 0.25. Meanwhile, look at the General Motors EV1 from a few years back. It looked pretty conventional yet managed a Cd of below 0.2. Aerodynamics isn\'t something you can eyeball with much precision.


Presumably, the extra weight of the tail must have reduced the fuel economy. I notice they don\'t say what mpg the car does, before and after. I have read that the average mpg of American cars has only increased by 3 mpg, since the days of the Model T Ford. It is apparently around 24 mpg. On this page there is an ad for cars that do 50 mpg. What is going on?


Congress should mandate easily reachable coefficients of drag. That way all our cars can be \'ugly\' and we can start exporting oil again. Boat tails, enclosed wheel wells, and an aerodynamic underside will allow most ordinary cars to get 100 mpg. Cost is near zero, since it is just sheet metal. See aerohonda dot com. In today\'s automotive market, cars must appeal to \'majority taste\' rather than to an aerodynamic standard. Americans, as a rule, have never preferred aerodynamic automobiles. Tastes will change with time. It is time to stop building \'stupid\' cars and build smarter, aerodynamic cars.


what was the dr.kamm tail all about?how much did it reduce drag? the alfa zagato long tail was redesigned with the bob\'d kamm tail and supposedly reduced drag.i suppose if the cars original design is stupid as a pontiacs usually is you\'d need a great compinsation as this tail seems to be.

Cowfy Kaufman

None of this aerodynamic chatter has referred to the brilliant Citroen ID19 launched at the Paris Auto Show in 1955. Just one look and you\'ll realize that Andre Citroen was light years ahead of the industry. Low CD, full belly pan, inboard brakes, full rear wheel coverage, low polar moment of inertia (engine behind transmission) and, of course, front wheel drive. Check it out!


interesting effort,,,,,,,,, some manufacturers are using rearview cameras instead of wing mirrors because of uneeded drag,,,,,,,,, the automotive world is moving on I\'m glad to say


The comments above were most enjoyable to read. I always thought that the basic Prius design made a bit slimmer would be able to hit at least 60 mpg with either a hybrid system or simply an ICE. Low Cd cars are on their way because auto companies will finally realize that their time has come.

Adrian Akau
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