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Old 02-21-2008, 01:51 PM   #1
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rear wheel air deflectors

since i'm getting incouraging results from the fairings i've put before the front wheels i've vinally decidet ist was time to do something about the rear wheels as well. at the time of this post the glue for the brackets to wich i'll attach the fairings is drying (as i didn't want to drill holes in an already rust prone area) but i'm still unsure about the size of the air deflectors

here's a sketch of the front view and of two things i'm considdering.

my dilema is: should i cover as much of the tire width as possible or will the air bleading of the straight fairing "jump" over the gap

does that make sence?

for referece the gti version of my car came with deflectors that had the profile of the last example but where faired with the sids rather than a flat barier (wich i intend to test before i'll considder something more advanced)
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Old 02-21-2008, 05:43 PM   #2
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With all of the added frontal area of that back tire, you would think that an air deflector would help the .Cd, of this car, but it had no effect on the .Cd - in fact when they raced the car at Bonneville, they even took them off.
Surprised me to say the least.

( Also. notice the gaping wheel wells. You would think they would try to divert some air away from that area ... but they were completely ignored.)
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Old 02-21-2008, 05:49 PM   #3
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Persoinally, I would test them both.
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Old 02-21-2008, 07:45 PM   #4
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I think the benefit of rear deflectors is signficantly smaller than front ones because there is already so much turbulence generated by the wheels in front of them and other underbody chaos. A likely more beneficial modification is skirting the entire sill to the same depth as the deflector but as wide as the tire, more effectively reducing the active frontal area of the tire itself.
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Old 02-25-2008, 07:23 AM   #5
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Perhaps my explanation was a bit confusing but what i'm taling about is a flat vertical deflector IN FRONT of the REAR wheels...i know, confusing... some cars have them before all wheels some only on the front ones... so the air hits these things and not the tires....


anyway what i want it to look like from above is this:




unfortunately while checking the bond one of the brackets it came off, the other one feels as if it's welded on so i think the first one used bad glue that had partly dried in the tip of the clue canister.

anyway, i have to reatach it tonight and wait for it to dry befor i can attach a real deflector and start "testing"
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Old 02-25-2008, 05:14 PM   #6
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Since some cars (SAAB? ) have them already it seems like a worthwhile project to follow.

I think the turbulent air will be present but the extra streamlining from the deflectors would still provide some gain.

I am interested to see what the outcome is.

Cheers , Pete.
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Old 02-25-2008, 06:50 PM   #7
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I've been thinking of using these....
http://www.powerflowinc.com/main/products/pro_fit.html
backwards in front of the wheels. Can't see the shape too well on their site, but they are molded shapes. I'd figure the ones that fit behind the front wheels should probably fit in front of the rear wheels if the body contours stay the same.

I'd figure on angling them slightly WRT to the airflow, since you don't really want them pushing more air under the car.
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Old 02-26-2008, 02:27 PM   #8
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Quote:
I'd figure on angling them slightly WRT to the airflow, since you don't really want them pushing more air under the car.
not sure about that... especially at the rear of the car. since you don't want to make your "wake" larger either... perhaps a little more air comming form under the back of the car is better than having it spill to the sides. afterall the air will be moved by the tire anyway so the fairings just there to do this in a slightly more orderly fashion i guess.

i also read somewhere, but unfortulately can't find the article again, that these plates where not angled was to maintain an equal pressure on both sides of the tire or something... otherwise you'd get instability... i don't know exactly how it went, just that an angle wasn't always as benefitial as one would instinctively think.

here's a picture taken front to back, you can see the lower tire portion is not well shielded



en here's the barcket i gued on with epoxy glue

the barcket is just an L shaped metal bit i glued to the botton of the sidesill.

now i can build the actual fairing!!!
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Old 02-26-2008, 05:51 PM   #9
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RoadWarrior -

Quote:
Originally Posted by RoadWarrior View Post
I've been thinking of using these....
http://www.powerflowinc.com/main/products/pro_fit.html
backwards in front of the wheels. Can't see the shape too well on their site, but they are molded shapes. I'd figure the ones that fit behind the front wheels should probably fit in front of the rear wheels if the body contours stay the same.

I'd figure on angling them slightly WRT to the airflow, since you don't really want them pushing more air under the car.
That's pretty cool. I didn't know of a manufacturer that made a *specific* version for your car. I only ever looked at the ones in AutoZone/Pep Boys/Kragen/ etc. and they never seemed to be a good fit. You'd probably still need to do some modification. I would spend time staring at the front and back interior of my wheel-wells to see if they are symmetric.

This is what I have right now on my front wheels :

Attachment 1216

They're just el-cheapo mudflaps. I don't know if they help. They look the same as the ones that other new cars have, so I figured that it would be ok.

CarloSW2
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Old 03-13-2008, 10:16 PM   #10
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Rather than using a flat surface placed roughly perpendicular to air flow, why not use a section of curved plastic, with the convex surface facing the wind?

You could make such curved plastic pieces by cutting a disposable plastic bucket in sections, like cutting a pie. Paint it black or grey.
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