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Old 01-27-2009, 11:37 AM   #1 (permalink)
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Wheel arches - shape

I noticed that most modern cars have similarly shaped wheel arches these days. Examples:

http://paultan.org/gallery/d/6134-3/...atria_neo5.jpg

http://lh4.ggpht.com/_QZCEofQMIcw/R5...MAM7-GOLF5.JPG

http://image.trucktrend.com/f/auto-s...ult-kangoo.jpg

In opposition to the old style:

http://upload.wikimedia.org/wikipedi..._Omega_A_L.jpg

The difference?

Nearly all new cars have wheel arches finished with vertical surface which is cut from the rest by a sharp edge. I wonder if it's just some concept of styling or is it somehow related to aerodynamics and fuel economy?

If it had sth to do with FE, I think I could try to adopt it in my Benz...

I hope You will understand sth from the pics. If not, I'll try to draw a scheme and drop it here.

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Old 01-27-2009, 03:22 PM   #2 (permalink)
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good question.

one thing to note is that car have an increasing wide track, this might be to improve handling,and since i have the impression most cars are a bit taller as well their center of gravity might be a bit higher as wel than the average car lets say 10 years ago.

styling wise these bold arches probably give the car a bit more muscular apperance... wich is a nice trick to give a small car or a potentially "boring" family car like the cangoo a bit more muscular appearance.

on the other hand i noticed you'r example of an "old" car is one of my favorites... and probably the one with the lowest drag of them all with and 0.28 Cd... so i'm not sure if these new arches are that much better than the old ones.

something else i've noticed is that on older cars there much more space between the wheen arch and the tire... probably because they had a little more suspention travle.
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Old 01-27-2009, 03:28 PM   #3 (permalink)
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Tightening the tire/wheel arch gap improves aerodynamics as well.

MaxMatt: the first two links you provided didn't work for me, so I don't really know what the examples were meant to show.

As for wheel arch design for best aero - a minimal tire gap, is best, plus adding a radius to the aft edge to permit air exiting the arch to make a clean transition to the vehicle side.

EG see: 60+ Vehicle modifications for better fuel economy - EcoModder.com

Low Cd production vehicles that took pains specifically to shape the wheel arches include GM's EV1, Solectria Sunrise (pictured), Honda Insight (gen 1)...



Toyota mentioned tweaking the wheel arch liner on the new gen 3 Prius, but I'm not sure if it's to address the same thing.
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Old 01-27-2009, 03:52 PM   #4 (permalink)
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After I noticed that straight vertical surface on few cars I started real-life observation and these style of wheel arches is actually on nearly every modern car:

http://www.ford.pl/spg/getImage.asp?...l_LC_13860.jpg

And that's on a pick-up!

And here - an older vehicle - curvy all the way:

http://www.mycompactpickup.com/inclu...ckup/truck.jpg

And an image of my production - it's awful, but I hope it explains something:



After looking at my own picture I think there is sth to do with wide tires better fitting in the new design, but it also reduces the space between the wheel and the fender.
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Old 01-27-2009, 05:48 PM   #5 (permalink)
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I'd vote for that being a styling item, but it lets you continue the curve into a wheel skirt with a simple transition.
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Old 01-27-2009, 08:20 PM   #6 (permalink)
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I can see a benefit for wider tires, but I can't really see an aero benefit... in fact, I see an aero penalty in the form of increased A.
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Old 01-28-2009, 02:12 AM   #7 (permalink)
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i assume they might be the "best looking" low drag approach to tires that sit outside the general bodywork, however i don't think they reduce drag...

the problem is what's the alternative? a wider body or a smaller track width, an overall wider body would give you more weight, canceling out the gains perhaps

imo lowering a cars roofline again would be a nice way to start... as this would lower the center of gravity
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Old 01-28-2009, 06:49 AM   #8 (permalink)
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I read a thread recently: Does lowering the car really help FE? or sth like that and I am quite puzzled. My car has quite smooth underbelly with smooth covers provided by factory. However, a friend after lowering his W124 says it feels more aerodynamic - he doesn't feel that much drag when pushing accelerator. Unfortunatelly no mpg stats from that source...

Here is how my wheel arches look now (not my car though):
http://www.w124performance.com/image...side_front.jpg

You can notice that the metal folds inwards. I thought that by unrolling it to reach vertical surface on the side would decrease the wheel-fender space.

By the way - here is a bodykit mounted on a coupe which helps aerodynamics, but I don't know if it's just about downforce or also reducing drag. Especially the front bumper looks similar to what we can see in Calibra.

http://img218.imageshack.us/img218/9...mmeramgcd3.jpg
http://i14.photobucket.com/albums/a3...24/W124_57.jpg
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Old 01-28-2009, 07:23 AM   #9 (permalink)
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lowering a car might help in two ways by lowering the car you expose less of the tire so you effectively decrease frontal area, although only just a little... you also cover more of the tire... you may have noticed a lot of cars have airdams that are lower in front of the tire than in the middle, the calibra is on of the earliest cars where this design was mentioned but a lot of modern cars more or less have this design some even have small plastic dams in front of the wheels. it's not entirely clear to my what the effect of shielding the front of the tire actually is, but if factory cars have this, i'm sure it does something.

lowering the car also reduces the ammount of air under the car... this might help to stabilise the air and it also creates a little downforce...

recently a lot of carmakers have introduced "eco" versions of their vehicles... i think VW more or less started the trent with their bluemotion lineup.

one of the things mentioned with most of these cars is that they sit a little lower than the standard model.
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Old 01-28-2009, 08:35 PM   #10 (permalink)
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Hi All,

The vertical section of the new fender style allows the fender to be narrower, for a given amount of tire vertical travel. I think it also stiffens the stamping, resulting in less noise. So, they may have noticed the aero effects - reduction in car cross section area, but probably did it to make the car fit narrower areas, and avoid fender drag scrapings, besides stiffening the fender.

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