Aerodynamic Tail Makes Geo Metro Even Cooler

[MetroMPG], an environmentally friendly car enthusiast from Ontario, added a tail to his car to increase gas mileage. This 1998 Pontiac Firefly is a sibling of the cheap and popular Geo Metro. He had already done some work to cover a portion of the rear wheel wells to reduce drag. Using cardboard, duct tape, and an aluminum frame he extended the rear of the car by around six feet.

The results are pretty impressive. His extensive testing can be seen in the video after the break and reveals a Miles Per Gallon increase of 15.1% at 90 km/h to get to 64 MPG. The tail is removable but we’re thinking it’s a pain to keep relocating the tail lights from the original body to the removable one.

Now we’re wondering if someone is doing this to our Smurf-blue Metro that we sold to the junk man for $100 back in 2001. It ran great, if you weren’t caught in the cloud of blue smoke coming out the back.

[Thanks Darin]

75 thoughts on “Aerodynamic Tail Makes Geo Metro Even Cooler

  1. omg… What has happened to the hackaday commenting crowd? Normally nice people interested in hacks… motors seem to bring out the freaks…
    Yes car might look odd, but great idea, 15% is great. I reckon someone needs to do a eco-kitcar. Something like the banham spider, light weight, streamlined, easily repairable (composite pieces to replace what you need) and cheap (fits of a common cheap car body)

  2. To suggest the weight lifts the front and creates a huge reduction in fuel use is pretty daft, but easily tested, go put something heavy in your trunk and see if you save on fuel, good luck with that one…
    And make sure you put some extra money aside.

  3. @kevin “Motorcyclists and bicyclists might take issue with your line of thinking”

    Yeah think of all the cardrivers impaled when they hit cyclists with aluminum bicycles… oh wait.

  4. @dstrcto

    “Andy, surface area has nothing to do with gravity”

    Of course it does you hold a big square peice of wood flat – then hold it on its side | see which is the lightest (Y)

    Also im glad you americans are looking into doing something to cut down on fuel useage instead of designing bigger chunky fuel guzzling trucks. The only reason i make my point is yeah the car will be fine long distance but driving in busy crowded areas, your stoping and starting constantly and that extra weight really doesnt help then.

  5. @Andy
    Time for some Newtonian physics!
    Andy, the gravitational pull on an object is relational ONLY to the mass of the body (Ie. The earth), the distance between the two, and the mass of the object (ie. the “Mod”). Surface area has bupkiss to do gravitational pull. If I have a 1x1x2 (length x width x height) foot object that has 1KG of mass, and a 2x1x1 object of the same mass… they both weigh 1KG on Earth!

    “Of course it does you hold a big square peice of wood flat – then hold it on its side | see which is the lightest (Y)”
    Your example is flawed. All you are doing is changing the pressure, but the mass (and thus weight) is the same. A 1KG paving slab weighs the same on its face or on its edge. It just means that it is not evenly distributing its weight across the face of the slab, but instead is distributing it’s weight across a smaller area.

    Now, surface area and aerodynamics.. you might say they’re linked ;)

    Oh, and these cars sold under the Suzuki name (“Swift) were built a bit better, with nicer lights, trim, and a 1.3 DOHC 4 cyl. with front+rear antisway bars… fun pocket rocket!
    The 3cyl is gutless stock though, but with a little work you can get more than 90 BHP without a turbo. With a car that only weighs 1500 pounds, you can have some good fun in a cheap runabout.

  6. I am actually a little surprised at the lack of knowledge here.

    First ANY LIFT up or down means more drag and less MPG’s PERIOD. there is no such thing as trading MPG for LIFT. “ANY” lift will result in lower MPG’s this is basic aero. Lift means energy expended which means “drag” which means lower efficiency.

    so if that tail DID generate any lift positive or negative ANY LIFT AT ALL it would HURT his mileage NOT HELP IT.

    the mass of the tail is irrelevant. he was doing “at speed” tests Newtons laws folks the mass was irrelevant to everything except his wheel bearings and thats so small you could never measure it with home equipment.

    ALSO you folks DO REALIZE we are talking about a geo metro here right? I have NO PROBLEM parking my 92 Clubwagon in normal parking space and I could fit his car INSIDE MY VAN TAIL AND ALL

    sure attach a tail like that to a Crown Vic or a Minivan or something and its going to be HUGE but your “TRUNK” in your current car is likely bigger than that tail is. GEO METRO folks. Tiny car :-) even with tail STILL a tiny car :-)

    the last guy. Andy. I am flabergasted. I truly and not sure how to reply to that.

    you ACTUALLY THINK the orientation of material object has ANY measurable effect on its effective mass?

    also THAT IS WHY HE WANTS TO MAKE IT REMOVABLE. so when in the city etc.. he can well REMOVE IT :-)

  7. also I am VERY happy with the 3cyl in my 94 metro. Plenty of acceleration plenty of passing power. I drive 54 miles one way to work almost every day with 4 people crammed inside my little metro. No problem (except people whining about the cramped quarters which stopped the moment I put my hand out for the $24 in gas it would cost to take the van hehe)

    I am surprised just how much power that tiny little engine has.

  8. @Chris Taylor: I agree w/ you totally.

    This is a great hack.

    I’d really like to try something similar for my pickup. Regular careless driving nets me ~24mpg, while I can achieve 28 mpg easily by slowing down and driving conservatively, and occasionally >30mpg being really careful w/ the throttle.

    I’d bet I could find >%25 better mileage by building a boat-tail to bridge from the cab to a dropped tailgate, tied into a smooth under-body panel. It is so noisy driving on the freeway, I’m sure there are huge improvements to be found. The original aerocivic modder guy said that the sound of the wind was nearly silent in his car when he was on the freeway from lack of turbulence.

    Sheet metal and dzus clips > duct tape and bailing wire.

  9. Sadly I think hackaday now needs a moderation system.

    As to the hack: Well done! Geo metros / Suzuki Swifts are awesome, i wish you could still buy them in the US. Oh well, when the hummers and excursions have guzzled up enough of the oil supply they will come back.

    Until then i’ll keep riding my 70cc honda motorcycle.

  10. @Chris Taylor

    Your argument about lift creating drag makes sense, but I feel you are too hastily brushing aside the traction of the wheel. Surely traction involves losses to friction. I’m probably arguing for arguments sake here, but it just seems like both of you could be correct.
    Perhaps it is possible that the mod creates some lift, and with it some drag. But this lift would decrease the normal force on the tires, thus redusing the frictional losses here.

  11. how many hacks on hackaday are ‘stylish’? How many are built to be functional? To test a theory? To prove something is doable?

    Why are people so obsessed with the cars looks?

    Also, about the comments on euro cars… Have you seen the cars most men and women drive in europe?

    anyway, great mod, great idea, good post and please someone banhammer offensive homophobes and general losers above. Shocked mainly at how awful their grasp of physics and basic aerodynamics are… A banable offense in commenting if ever there was one (JOKE!!!)

  12. what about an inflatable body wich u might deflate for parking, when u do highway travels you just press a button and have that 15% or maybe 20% mileage improvement. Maybe if you put many low cost improvements together would be possible to extend even further fuel economy, thinner wheels, stronger spark, wider air intake and out-take and so on.
    The analysis is very worthy on this hack, congrats

  13. @le’chef: Downforce also creates drag, but not because of tire friction; it increases drag because it’s the same force as lift, just in the opposite direction. Any time you create lift you’re creating drag. In aircraft this is called “induced drag.” In simple terms, the energy to create the lift force has to come from somewhere.

    Decreasing weight on the tires could in theory increase fuel economy by reducing sidewall flex, but I doubt this mod is creating enough lift to even cancel out its own weight.

  14. @Orv

    What in the hell are you talking about? Drag is the resistance in opposition of thrust. The engine used to move an object through any medium(air for aircrafts, water for submersiable crafts, both for floating vessels) must take into account the energy to displace( push around the vehicle) the medium itself. The more streamlined the vehicle, the easier it is to push through and less energy is needed for displacement. This energy can then be used for thrust.

    Induced drag is an intended effect used by aifcrafts to slow them down( air breaks). The wings normally open up flaps to reduced the lifting effect of the wings so that the plane can slowly land without crashing into anything on the runway( else we would need longer runways).

    In conclusion,lift works in opposition of gravity. Downforce works in opposition of lift( good for race cars, dangerous for aircrafts). Drag is in opposition of thrust( in the opposing direction of travel). Lastly, thrust is the application of locomotive force to any object to make it move in any direction( engines generate, drives translate, and I’m always late regardless. lol)

  15. In the old days (VW beetle) they though easing up on the flow like this was aerodynamic, but now they know it is best to cut off abruptly (hence the name, spoiler).

  16. @shiekh,
    No, that is not correct.
    Spoilers are for cars that have such a stupidly high power to weight ratio, that the back weeks need pinning to the floor, lest they will spin out. Since they don’t want to carry unnecessary weight for stopping/starting.
    Spoilers pin the wheels down with the downward force, that force takes away from the efficiency of the car (a trade off they are happy to make, but is not needed for any normal car!)
    Any ‘normal’ car you see on the roads with a spoiler is wasting fuel (guessing they don’t care if they think it looks cool) as they are rarely going to reach the speed to make use of the down force.
    Spoilers are only really good for cornering fast! like f1 cars do… Cornering slow with a spoiler is pretty pointless. Using a spoiler at a steady speed (on a motorway for example) is pointless. Guess only good point would be if you need to take evasive action on speed.
    But never confuse a spoiler with a tool for aerodynamic efficiency.

  17. I wonder if he could put some Fiber Optic cable from the original Tail lights leading to the new Tails’ tail light, so no modification is needed when he attaches or removes the tail.

  18. @crow

    “But never confuse a spoiler with a tool for aerodynamic efficiency.”

    Never say never. ;) Depends on the spoiler and what it’s attached to. In the right context, a spoiler will indeed achieve greater aerodynamic efficiency (reduction in turbulence, etc.).

  19. Indeed nateL – I do stand corrected there. The thing that gets me is people don’t notice that by it’s very name the idea of a spoiler is to spoil and redirect the airflow.

    Yes – that redirection can be used for aerodynamic gains, but generally it’s to hold the wheels to the tarmac without additional weight.

    Nothing like replying to a comment to a post from 2009! ;)

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