Wheel well vents
 

I saw a WRX the other day and noticed that there are vents at the rear of the front wheel wells. I've read tips about aero and remember seeing that radius'd (Is that a word??) wheel wells are better. I'm guessing this is because air can be "caught" by the rear of well and cause more drag? This got me wondering if the WRX vents actually work and if other cars with bulging fenders could benefit? The new beetles come to mind first but I'm sure there may be others. Can anyone weigh in? Am I on the right track or more confused than I thought?

Reference pic: http://www.inautonews.com/wp-content...va-2014-18.jpg

The wheel vents are purely cosmetic...there is nothing behind it :(

Yes, i've come to the same conclusion as you. I plan on removing those "vents"...and then fiberglassing a smooth radius transition aft of the front wheel well on my sti

however, not sure if it will give me any benefit

I have seen whee well vents on several cars and also wondered about their effect.

The wheel well is a vacuum place as far as I know (setup used to cool Austin Minis) so a vent at the back does not sound like a good idea unless the front end of the car is designed to pressurise the wheel well.

Thoughts ?

Wrx
 

The USA version is Cd 0.30?
The 1986 Subaru XT was Cd 0.29.
The 1982 Firebird Trans Am extractor vents ADDED drag but were left for aesthetic reasons.
Professor Alberto Morelli's handling of the vents on the CNR 'banana' car would be the global benchmark for vent efficiency.
Tricky stuff!:p

http://i1047.photobucket.com/albums/...27-08_1905.jpg

These vents were real; they vented the engine compartment, not the wheel well, and I don't know how effective they actually are. I'd bet this is the same on most sports cars with this feature, or nonfunctional and cosmetic. The outgoing Mercedes E-class vented the rear wheel wells, exhausting that air through vertical slits on the taillights.

that is such a badass car.... :eek: ......(sorry :o I digress)

So, you drive with your window down and you have your engine venting in front of your door?

Viper
 

I think the Viper has the same Cd as the RAM 1500 pickup,so I don't know how much good the extractor vents did for the car.They're never used in low-drag concept cars,except the 'banana' car.And at Cd 0.201,the 'banana' car is kinda at the high end of low drag.

What about the Viper's rear vents ?

rear vents
 

*They're right at the rear separation line and hopefully emptying into the wake.
*If the pressure at the rear wheels wells is lower than that of the wake's base pressure,then air would actually flow forward into the 'extractor.' You'd have to be vary careful.And something you could only do in a wind tunnel.

My understanding is only front wheel wells can be made to be above car's outside pressure through ducting from the front ....

I also had a Ram SRT-10 at one point (that's where my avatar comes from), and that was listed by Dodge at Cd .45; the 2002 GTS was a claimed .35-.36 or thereabouts if I remember correctly.

Those are the pressure-relief vents from the trunk. Every car has them, usually under plastic panels and venting under the exterior body panel, or in the back of the cab on a truck. I was disappointed they weren't more exotic.

Aw, shoot--it was the C-class, not the E, with the tail light vents.

http://www.motortrader.com.my/news/w...cle_1108/9.jpg

there is very little about the viper(especially the earliest ones) that is designed for operator comfort, it is a very good example of a car that sets its sights on a single goal(raw, nearly uncontrollable power with everything else in the car being secondary) and doesn't stray from the path very much.

i would never want to own one, but i would certainly not turn down the chance to beat on it for a little while.

Thanks for the replies gents. In the back of my mind I knew the vents were cosmetic but got me wondering none the less. So basically cutting up the front flares of someone's beetle is a bad idea, aerodynamically speaking???

Great! I was looking for this image or for the concept in general for the bumper holes thread!

The front wheel well vents are in most of the badass sports cars (Ferrari F40, Enzo, McLaren F1 and P1 and even the Bugatti Veyron, which is made with a low Cd in mind to achieve its high speed record) and they have the engine at the middle, not at the front. In normal sports car they are purely cosmetic, as they are sealed. I know these cars are not ideal when talking about Cd, but maybe we can learn something more about their aerodynamics.

Looking a bit I found this info from BMW.

BMW EfficientDynamics : Aerodynamics

It has many things that are well-known here, but the vents on the side caught my attention

Actually I had the 4 series from BMW in mind when I got interested in this thread.

From the BMW website:

4 Series-
"Aerodynamics.
The entire vehicle design is testament to the BMW EfficientDynamics philosophy. The optimised, aerodynamic front apron and undercarriage feature innovative improvements that reduce air resistance and fuel consumption.
The front apron is a prominent design feature that embodies the BMW EfficientDynamics philosophy. The integrated Air Curtain channels air through two vertical air inlets and along the front wheel arches. The accelerated air flow creates a kind of "curtain" on the outer side of the wheels. Then there is the Air Breather, which channel the air flow at the front wheels. These innovative BMW EfficientDynamics technologies reduce turbulence and air resistance, which in turn significantly reduces fuel consumption.

The flat undercarriage cover, which also shields the engine compartment, is an additional detail that greatly improves the car’s aerodynamics. This new trim elements are not only highly advantageous in terms of aerodynamics: they also improve sound insulation and provide greater protection from rust.

The Air Breather is located behind both front wheel arches and is one of the innovations used to optimise the vehicle's aerodynamics. Together with the Air Curtain in the front apron, the Air Breather greatly reduces turbulence and accurately channels the air flow. This decreases air resistance, thereby reducing the vehicle’s fuel consumption and CO2 emissions."

I think a lot of supercars have functional wheel vents as well, but you probably need a wind tunnel or else you might be making your aero worse.

I'm loving some of the things BMW did with that 4-series. The back has a small kammback it looks like, aero wheels, grill shutters AND the vents that were the reason why I started this thread. If anything, I think BMW proved my idea that cars with some kind of fender bulge might benefit from a small hole cut in the rear of the bulge. Ideally this would be experimented on a car with an already messed up fender from an accident or small animal impact. Something tells me that this won't increase MPG by 500% but I wonder if it's something that might show increases outside of the normal noise if checking MPG...

And could maybe be a more simple, more attractive mod than front wheel skirts that nets almost the same gain...maybe??

Apparently, Subaru are using them too, as well as the frontal deflector(?) to guide the air to the sides.

Thanks to kach22i who posted the image on the "Random Wind Tunnel and Smoke Pictures" thread
http://www.subaru-globalws.com/s001/...984-lg_img.jpg

The far upper right image suggests that the wheel well vents are NOT purely cosmetic. The question remains though, is it beneficial for fuel economy...

i still find it hard to believe the front vents have any aerodynamic benefit.

i popped off my front vents on my Sti... there is only a single 2" diameter hole behind that vent. i doubht that 2" hole is big enough to cause 3 arrows of air to flow out of that vent

I this the new version of the "10lbs of crap in a 5lb bucket"?? lol

I can't imagine that "normal" cars would need much venting of the wheel wells, so the 2" hole might be enough to relieve any high pressure building up in there. Again, I don't think that there would be impressive gains made but it might be something to think about doing.

The idea is to use high pressure from the front to offset depression from underneath.

Wheel well vents, now that I think about it might only work as one way exit only.

Excess pressure might leave through sides of the tires anyway ...

Your car is an older model though. It looks to me like the vents are intended to provide an air curtain over the front wheels (which you wouldn't need if you had smooth wheels...).

I'm thinking of trying this on my Wrangler's plastic fender flares before I fit new wider ones. It seems like given the air gap to the tyre an aweful lot of air could get trapped in there, esp. the 7+ inch wide ones. I could even try a little 'CAD'. The problem is the flares still need to stop rocks and mud from being ejected out the back.

I think the OP is talking about the vents "behind" the front wheels....

Here is what is underneath the vent "behind" the front wheel

Thinking about the vents that are on top of the fenders of Le Mans prototype cars, I did a Google search and ran in to this thread on a Miata forum for reducing wheel well pressures.

Automotive Aerodynamics - Sport Compact Car Magazine All Pages
Extracted article from the link :

I think the vents at the top of the wheels are not beneficial, they're there as a safety measure to reduce lift in certain accidents. There was Porsche magazine that said this.

In that thread, user lightyear has a nice setup :D His modified fender has the radiused edge that aerohead has mentioned before.

Well, would you look at that. I can't imagine that doing much good at all.

Has anyone tried doing an air pressure check, like was mentioned in the miataturbo forum? I might consider that, once I get some time. My truck's wheel well openings are all radiused, but I'd like more ventilation since I've got a belly panel installed. My first thought was to put a vent aft of the front tires, hoping the passing airstream would draw hot air from the engine bay. But on second thought, that may not work since the tire is blocking the airflow, and I have mud flaps (I don't like rock chips...). Would a vent on the front side of the wheel tub work? I'd think the air would be moving down towards the ground, given tire rotation, and would draw air out of the engine bay...but haven't tried to put the theory into practice.

My reasoning for starting the thread was an idea from an observation just under the assumption that the back half of the wheel well traps air and is a parachute of sorts. Ideally, radiused wheel wells would be used like on these club cars with the back 1/3 of the flare cut off. But since paint protection is a concern for most who drive their cars more than 1x a week and not on a race track, I thought the vents would be a good alternative and possibly (if they work like I'm thinking) be a cleaner, better looking alternative to wheel skirts. Skirts would be ideal but some aren't willing to take the plunge so if you could add a vent and get 75% of the benefit as making a skirt, it could be worth it. I'm guessing that the larger the space between tire and wheel well, the more air is trapped and the more benefit could be had from wheel well treatments of all kinds. Flared fenders like those on STIs and VW beetles would be easiest to do it on, but some creative ducting could be used to adapt to any vehicle much like how BMW did it with the aforementioned vehicle.

In regards to the Jeep comment, large fender flares will catch a lot of air but to cut off the last 1/3 would mean all sorts of debris from the tires getting kicked up and hitting the body and possibly the driver. Cutting an opening and attaching down facing vents or a small-ish screen could prevent body damage while alleviating some parachute affect of the flares.

On engine cooling: those with full belly pans have to exhaust radiator air/heat somewhere. I've seen a few that do it into the front wheel wells. If the pressure in the wheel well is high, then it could prevent some cooling as the max amount of air isn't being allowed over the rad. Venting the wheel well at the rear could possibly help maximize cooling as well if it drops the pressure substantially, Right? Otherwise a fender vent connected the engine bay would be needed (assuming the engine bay is completely sealed off)

Something else to ponder, courtesy of Ferrari. These obviously would not work in combination of a mud flap or stone guard, but here we go:

The area behind the wheel of a 599XX Evo:
http://www.ausmotive.com/images2011/...-EVO-video.jpg

I had the fortune to view one of these 599XX Evos at the 2012 Rolex 24 at Daytona that was on display. Also on display was a 333SP which also has a front fender treatment, similar to the one shown below:

http://www.allsportauto.com/photoaut...3-sp_10_sb.jpg

Going back to a stone guard, note the 333SP has clear plastic or curved plexi to protect the paint from rock/dirt/tire debris; this could be worth considering should one go this route.

Interesting. Does this example works best with a rear engine car, or if like in the case of the Miata, the configuration of the engine doesn't make a difference and the is just the BEST way to get airflow out of the front wheel wells.

I wonder also how having front wheel skirts would affect the entire concept?

The 599 appears to be front engine as evidenced by the exhaust pipe. Wheel skirts would eliminate the need for the "rear of well" treatments because it would eliminate the trapping of air in the area. Vents could be a close sibstitute to the major cut outs of the race cars is my thinking.

parachute effect
 

I'm not certain that the wheel well aft of the tire catches any air at all in the context of a parachute.A parachutes drag is created from the all-separation,enormous turbulent wake above it.
A pool of dead air may just travel along with the quarter panel,as with a rear bumper,with the active flow just ricocheting off the dead air.