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Old 11-13-2008, 10:58 PM   #101 (permalink)
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I haven't driven the car a lot with the skirt on, but so far, I can't see a situation where your road speed (air speed) would be high enough and the steering input great enough to "open" the skirt at a bad time.

Try it next time you're driving - a quarter turn is where my tire contacts the plastic backing on the skirt and starts to push it. A quarter turn is a lot of steering input at, say, 45 mph.

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[Edit: If your 90-day average goes up noticeably after you get the front skirts on, that'll be good enough for me!
My 90 day fuel economy is about to go down significantly. Long road trip coming up, and I'm NOT going to be averaging 30-40 mph for those 1000 miles. Also: winter!

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Old 11-13-2008, 11:27 PM   #102 (permalink)
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Quote:
Originally Posted by Cd View Post
I suspect that this is why that todays cars are on average what seems like 4.5 " - to over 6" taller than cars from just a decade ago.

Have you ever seen a new Fit / Scion / or even a Prius next to an older Civic or Metro ?

I'm going to create a seperate post about this ( trying to get guesses as to why that the cars are becoming so tall and narrow ) It makes them look cartoonish.
( I had read of designers creating things larger for Americans increasing hip sizes, but it strikes me as odd that cars are increasing more in height vs. width )

Back on topic folks : About the wheel skirts, is it possible to create a lip that seals the gap when the wheel is turned, or does the arch of the turn prohibit this ? It seems like this would be a good way to keep air from catching the assembly and tearing it off .... then again you could use heavy duty springs like BassJoos
My guess is that the height is increasing because that is what the humans are doing. Every generation is taller than the last. If you ever look at 50's furniture, it's much much shorter than furniture now. The same with houses and doorways.

The "trendy" cars aren't getting any wider or longer, because here in the US, we are following the Europeans in the need/desire for cars that have a smaller physical footprint.
We want to be able to fit more cars in our driveway, into smaller parking spots, and be able to squeeze into the tiniest gap in rush hour traffic.
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Old 11-14-2008, 01:17 AM   #103 (permalink)
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[QUOTE=Tango Charlie;72058]Dittos on all the congrats. It looks great!



That nice smooth taper aft of the wheel is producing some sideways lift, eh? (trying to speak your language, eh? )
Lift does produce drag. It would be an infinitesimal improvement, but I wonder if you could eliminate the production of lift without increasing drag? This got me thinking about lift produced elsewhere on cars, but maybe that should be discussed elsewhere...

Those trailing edges are lifting because the air on the outside is moving faster than the air on the inside, but there are such pressure variations all over streamlined cars. They cant' be avoided, but they can be harmonized to avoid turbulent drag.
"Lift creates drag" refers to induced drag from leaving the wake moving in one direction, while these forces are averaged out from each side.
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Old 11-14-2008, 03:43 PM   #104 (permalink)
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Quote:
Originally Posted by Ernie View Post
...The tire rubs right on the material...
I think it's probably a good idea to have some sort of sacrificial part that the tire can rub on, rather than the cover itself. If you use these over the long term, they will wear--you cannot avoid it! It's better to have a part that can be relatively easily replaced and won't affect the cosmetics or the important bits that the air is flowing over.

I wonder how hard it is to get sheets of teflon-covered plastic? Or sheets of a nice slippery plastic? Those would make for good sacrificial rub strips.

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Old 11-14-2008, 04:14 PM   #105 (permalink)
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McMaster-Carr has pure teflon sheets as well as teflon coatings. However, a thin steel sheet would rust away before it would wear - see the spoon brakes on primitive bicycles.
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Old 11-14-2008, 04:47 PM   #106 (permalink)
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Originally Posted by some_other_dave View Post
I think it's probably a good idea to have some sort of sacrificial part that the tire can rub on, rather than the cover itself. If you use these over the long term, they will wear--you cannot avoid it! It's better to have a part that can be relatively easily replaced and won't affect the cosmetics or the important bits that the air is flowing over.

I wonder how hard it is to get sheets of teflon-covered plastic? Or sheets of a nice slippery plastic? Those would make for good sacrificial rub strips.

-soD
If you read this thread posts 83 through 87, you will see he did use plastic for rub strips.

http://ecomodder.com/forum/showthrea...html#post71950

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Old 11-15-2008, 01:02 PM   #107 (permalink)
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Just some thoughts.
I have had some experience with tire rub on the inside on a van and a VW type 3 both of which I have owned for 30+ years. (resulted from tire profile change.)

If the rubbing can be made to happen on the tire tread I seriously doubt you will ever hurt the tire as it rubs on the road 100% of the time.

I would try just fabricating with metal for the rub area as it can be very thin and steel strong which will minimize the actual contacts by keeping a maximum amount of clearance between the tire and the skirt. On my VW I installed a 1/16th inch thick teflon rub sheet and in a few years the teflon had a hole in it. Once the tire hit the metal of the car the area has just stayed shiny and there is no indication that it is ever going to wear through.

In both of my cases the rub is trailing edge and only at very slow speeds and at near full lock. But the car certainly doesn't move away with the contact.

It is interesting that the solar racers all seem to use height to get the best cd. Obviously they have more control over the shape of things. I think it is the the solar car from McGill University that has full wheel fairing that just sort of "fly out" on there own in turns. Now, that might be a great way to get to know the local traffic officers. Wave at them in the corners with your front fenders.

Looking good.
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Old 11-16-2008, 12:00 AM   #108 (permalink)
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I would say that you should reduce the coefficient of sliding friction to a minimum in the rub spot. Wear occurs much slower in areas that are smooth, like bearings or precision ground camshafts, for this reason alone. Just get some Teflon, slap it on there or some other very low coefficient of sliding friction material. Rollers like basjoos would be best. At the very least, one could sand and polish the rub points to reduce it.
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Old 11-16-2008, 01:27 AM   #109 (permalink)
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The challenge, unlike bearing surfaces, is the tire is always getting dirty and bringing grit up to the plastic wear surface. I'll be interested to see after some driving how much wear there is. I'll keep you posted.
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Old 11-16-2008, 07:54 PM   #110 (permalink)
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Well, I don't know if it's the front skirt or the Kammback, but today I had a couple of really obvious reactions to the car on the freeway: teenage passengers in two different cars gleefully pointing as they passed. It made me laugh.

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Ecodriving test: Manual vs. automatic transmission MPG showdown



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