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Old 10-19-2008, 10:06 PM   #1 (permalink)
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Free: spring-loaded air dam in San Bernardino, CA


This was the first air dam I built for my new Smart Fortwo Pure. I cut it from some PVC sheet I had laying around and mounted it on a spring-loaded hinge so it would flip up against the bottom sheeting if I hit something like a thrown truck cap, but easily snap back into place with a simple pull.

It was kind of an experiment to find out how effective it would be on the Smart. It scraped a lot because I mounted it way loooooow for maximum aerodynamic effect. There was a question about whether or not the drag induced by the dam was greater than the drag it eliminated because the Smart has a pretty clean underbody. I use a 7-mile downgrade and an anemometer to try to verify aero mods. It seemed to go a lot faster so I was getting pretty stoked about it when I left for Phoenix.

I was convinced at the time that I was getting better mileage but I didn't really get enough time to test it. What was absolutely certain was that it was much more stable in crosswinds. Dramatically more stable.

But then disaster struck. I was drafting a truck in heavy traffic (for survival, not mileage) on the San Bernardino freeway before the overpass into Riverside when I hit a thrown truck cap. Unfortunately, this cap was folded over on top of itself and was sticking up pretty high, pretty high like 5 or 6 inches when I rammed it. There was a really loud bang. I pulled into a rest stop near Needles to pull the air dam back out but it was gone.

It's yours if you can find it.

The next dam will be more forgiving. Maybe bristles or something. I've been looking at plastic broom heads with poly bristles that I could cover with cheap, sacrificable pvc sheet or tape. Still thinking about it.

With bristles, I could let some air out of my tires and sweep parking lots for gas money.

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Old 10-19-2008, 10:23 PM   #2 (permalink)
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Hey, welcome to ecomodder, Ptero!
If the airdam produced that much of a noticable difference, I would encourage you to try again!
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Old 10-20-2008, 12:23 PM   #3 (permalink)
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Welcome to Eco-Modder
Sounds like a great Idea; Do it again!
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Old 10-20-2008, 01:24 PM   #4 (permalink)
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What did you use for the spring mechanism?
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Old 10-20-2008, 09:00 PM   #5 (permalink)
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I wanted it to break away rather than cause damage to the Smart, so it was pretty light and only held in place by two belly panel screws. Two six inch 3/8-inch dia springs were attached to openings near the lights to short rods protruding from the top of the air dam to hold it in place under tension. If it encountered an object, it would pivot on short brackets, rotating slightly down and rearwards, and it would fold upwards in the center. The springs would wrap downwards and loose their pull and the dam would remain horizontal until you pulled it back, then it would snap into place. It survived several previous thrown caps before it broke free, and when it did, it just sheared the heads off the mounting screws and straightened out the spring hooks, taking them with it. Like it was never there. I really liked it. But the scraping was pretty irritating. The wheelbase of the Smart is so short that when you hit the brakes, the dam would scrape. The amazing thing was that after a LOT of scraping there was absolutely no loss of plastic at the base of the dam. It was just noise. It made pedestrians drop things.

I've decided you can't do an air dam on a Smart without adjustable air shocks. Oh, and I'm going to drop it a couple inches by modding the springs when I get them.
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Old 10-20-2008, 11:21 PM   #6 (permalink)
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I love the idea of a break-away air dam. Seems like the biggest problem with these is hitting curbs and speedbumps. Something that flips up solves that!

Hmmm. - broom bristles....
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Old 10-21-2008, 09:19 AM   #7 (permalink)
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Quote:
Originally Posted by Ptero View Post
...But the scraping was pretty irritating... It made pedestrians drop things.
That's funny right there! I'm just ornery enough that making pedestrians drop things would be reason enough to install an airdam!

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aerodynamics, air, dam, smart

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