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.
https://www.fuelly.com/attachments/fo...6fc1d26b3f.png
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)

https://farm3.static.flickr.com/2109/...23b2c475_b.jpg

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.)

Persoinally, I would test them both.

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.

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:

https://www.fuelly.com/attachments/fo...8cec04ddd0.png


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"

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.

I've been thinking of using these....
https://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.

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

https://www.fuelly.com/attachments/fo...32349c4d32.jpg

en here's the barcket i gued on with epoxy glue
https://www.fuelly.com/attachments/fo...94bdeeff15.jpg
the barcket is just an L shaped metal bit i glued to the botton of the sidesill.
https://www.fuelly.com/attachments/fo...ee1bcaa591.jpg
now i can build the actual fairing!!!

RoadWarrior -

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

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.

One of my quests has been to find the "perfect plastic dustpan". Just cut off the handle and zip-tie it under the front wheel of the car. But, most dustpans have something wrong with them in terms of their shape. They are too complex for my needs. Just not right in some way, :( .

CarloSW2

Looks like someone beat me to the reverse mud flap idea.
I can't seem to find any locally for my car. Wierd.
I guess I'll have to check the junk yards.

i've currently installed some corugated plastic "revese mudflaps" on my car... i'll take pictures when it's light outside. i'm still looking for a better way to attach them though... curently they have tape at the top, wich i wanted to replace with the mechanical clips from my original mudflaps but this didn't seem to work.

while i was at it i tried to test fit the original mudflaps in reverse but that didn't seem to work.

they where much bigger than the plaps i'd conctructed and wich i feared would be oversized! they're much heavyer and in the end they where designed to fit perfectly in their original location to this made them fir all the worse it a reverse position. the ones that would go behing the front wheels worked best when placed in front of the rear ones because the profile of the car doesn't change much between the wheels but iltimately they'r require a lot of cutting to make them work so i decide to stick with the ones i've made.

i really like the idea of recycling old tings with interesing shapes, but i've had very little luck with them... they never fit just right. imho you're better of with a flat sheet of plastic than with something that almost looks like the thing you need but won't work in the end. than again you might get a lucky find sometimes :).

as for the aerodynamic propperys of these flaps... i think they work rather well, i haven't ran trough a tank with them, but the car seems more stable and prehaps coasts a bit further. so if there's a measurable difference, or at least not a big drop in fe i think they'll become a permanent item

This is what the rear wheel air deflector looks like on my car. It is made of a piece of aluminum angle screwed to the underside of the car with a piece of coroplast screwed onto it. I initially made it 2/3 of the distance to the ground and then trimmed it down to where it didn't rub the ground when I hit bumps.
https://www.fuelly.com/attachments/fo...35799cc1f4.jpg

https://www.gassavers.org/garage_imag...zvfcocoqbu.jpg here's mine: aluminum cans,coke bottle and duck tape.https://shutter11.pictures.aol.com/da...b21uRD00A0.jpg

heres what i'm evaluating
https://www.fuelly.com/attachments/fo...1b69d89cf4.jpg
https://www.fuelly.com/attachments/fo...6213af5210.jpg
it's mainly held in place with the bracket i gluen on and it's secured over w lip tat portrudes into the wheelwell. the top is a problem, for now its taped on to prevent it from vibrating but i'm looking for a more permanent solution.

unfortunately with last nights rain they got a little sandblasted and that took most of the paint of.... now they look suspicious again :)

btw why does a slightly dirty car always looks like you took it offroading in a picture? :D

I'm putting air dams in front of my tires too.

The rear one which I added a while back seems to have helped me reach more often 27MPG on highway, though it is very hard to be definitive about this since there's so many factors that come into play.

My application is a 2002 CR-V SUV, so very high off the ground. Removing air from under the car is not an option for Cx, so I want it to flow as best as it can.

If you look at modern cars, you'll see the air dams for the rear tires are just tiny square brackets, no angling, so I suspect that they measured it as being the best solution.

I just did the front ones, yet untested:

The front dams are not like mine, they usually are 1/2 tire in size, and I don't know why. Different constructors place them at different locations, often covering the 1/2 inner side of the tire. My CR-V's design is odd, with the wheel mostly uncovered by the underside fender, which is atypical. Maybe it is to improve the off-road passing ability. Maybe it is a different aerodynamic solution. Time will tell.

My Wheel Airdams

https://membres.lycos.fr/sonyhome/Hon...s/IMG_3860.jpg

Here's the rear ones, with angles...

https://membres.lycos.fr/sonyhome/Hon...s/IMG_3865.jpg

May I kindly ask for updates on this subject?

Do you drive a CR-V too?

You may ask my results!... Not great.

I fooled around with my scangage, but the bottom line is I think the front deflectors as I made them are either useless or even detrimental. The rear ones seemed to help a little when I had put them in.

I don't know why they don't work. Too far from the wheel? Too big?

The thing is I got poor gas mileage this week-end. I think in part it's because I was not driving but still. I was getting 25~26MPG driving, but my friends were in the 19-22 MPG, and I did not drive highway, seemed to be low MPG.

This compares to EPA on www.fueleconomy.gov:
old EPA: 22-26
new EPA: 20-24
drivers: 20-27

i never got the deflectors to stay on propperly to test them well enough. they where in a classic rust spot for the car so i didn't want to drill or anything.

the car did feel more stable with them on, but not like that alone would be enough reason to keep them.

i've since changed cars, but have already installed front wheel fairings wich don't seem to hurt as milage keeps going up. the front of the rear weel arch is roughly similar, so attaching anything will be a pain again... i've tried fabricating some clip on brackets but failed, but i definately want to bring them back.

for the moment i focus on an undertray however.

Lunarhighway:
* Maybe corrugated plastic is not the right material for you. Have you tried harder plastics like ABS or polyvinyls? That's what I'm using. Those flex but are pretty hard. Also can be heat shaped and come in black so no painting required. Once scratched or dulled, they look stock.
* To attach, have you tried to screw them onto the plastic lining in the wheel well (if your car has that)? That can be drilled without causing rust.

My CR-V has a high clearance (8"/20cm), so an air dam would add a lot of frontal surface, which is why I was hoping narrower wheel deflectors would help MPG. Since this is a week-end outing vehicle (highway/big cargo/light offroad), I care most for high-MPG on highway.

I am not sure where to go next:
- Re-measure
- Remove the front wheel air deflectors
- Re-measure
=> Make a design call (maybe narrower deflector like other stock designs)
- Re-measure

I also want to do underbody work:
I bought a long rubber runner I want to attach to smooth the underbody and soundproof. The gas tank sticks out like a brick, and the rear bumper has a big hole.
I am also considering getting air foils like air tabs for the back of the SUV, and maybe for the front on the hood. That would require wind testing :\
... Well those are off topic here.

What are the definitive test results for all of you who've put air deflectors?

on the vectra i used the lids of two spindles of CD-r's just cut the top of and trough the side and unrolled them and than screwed to the plastic liners of the front wheels, the front of the rear wheel arches however is all metal (wich is the spot where a lot of these cars rusted beyond saveing...)

here's the front deflectors on the vec
https://www.fuelly.com/attachments/fo...ce509e4ddf.jpg
along with the test untertray
https://www.fuelly.com/attachments/fo...735168ede4.jpg
gave them a shot of black paint form the back, and since they're transparent that gives the font a shiny black look that can't be sandblasted of as happened on the kadett.

they don't shield much of the tire but they do keep air away from the suspenttion link and the wheel well cavity, wich i think might be more important.

i'm considering enlarging them as they might work better if they where bigger, but i think i'll refine my undertray first. also too small will still save gas (or do nothing at wosed.... to big will waste gas as it adds drag over stock!)

do you have some pictures of what you made? would be nice to see , even if you think they're not right

For those with deflectors and reading this:

Anybody have significant MPG gains measured from their deflectors? If so what do they look like and what do they really shield?