Environment Transportation Guy Adds Boat Tail to Car, Increases MPG by 15.1% By Jerry James Stone Writer California Polytechnic State University Jerry James Stone is a food blogger, vegetarian chef, activist, and internet personality who started writing for Treehugger in 2004. our editorial process Twitter Twitter Jerry James Stone Updated October 11, 2018 Migrated Image Share Twitter Pinterest Email Transportation Automotive Active Aviation Public Transportation Image courtesy of Wired Darin Cosgrove has increased the fuel efficiency of his car by 15.1% by adding a homemade boat tail made from cardboard, aluminum and duct tape to the vehicle. This isn't the first mod he's made to the '98 Pontiac Firefly (that's Canadian for Geo Metro)--Cosgrove is the founder of the hypermilling site EcoModder.com. This particular addition extended the car's back end by 4.5 feet. In fact, Cosgrove figures with all of the modifications he's made that he's actually cut the car's drag coefficient from 0.34 to 0.23. Image courtesy of WiredYou can see how he calculated that coefficient over at his website. "I've driven with the tail on for about 300 km in total, mostly at highway speeds up to 100 km/h," Cosgrove told Wired. "I didn't notice any change in handling. The only effect on driving is I have to watch out for rubberneckers in other cars. Seriously." The boat tail mod took him about 14 hours to complete. He's been so impressed by the results that he's already planning a more durable version. "That 15 percent is just from the tail: multiple bi-directional averaged runs at exactly 90 km/h (56 mph) on a straight and level road, absent other traffic," Cosgrove said. "The tail was removed and reinstalled during the test so the 'A-B-A' comparisons could be made in identical conditions." It's doubtful you'll see this on a production model anytime soon, if ever. Still...it's another wicked use for duct tape. Image courtesy of EcoModder Image courtesy of Wired Source: ABC ScienceSee alsoMike Turner's Do-It-Yourself 95 MPG AeroCivic (Slideshow)DIY AeroCivic: It's Ugly, But it Gets 95 Miles Per GallonLike this article? Follow me on Twitter or friend me on Facebook.