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Old 09-19-2017, 12:35 PM   #1 (permalink)
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Aerodynamics behind tires (to add a fairing or leave open?)





Was reading an article on A Brilliant View Into Aerodynamics - Speedhunters.

It struck me as odd and possibly contradictory that the images actually seem to recommend having an open area right behind the tire (virtually no fairing), as opposed to a fairing directly behind it gradually sloping inwards. Even though, obviously, those designs still push/keep air away from the front and sides of the tires.

Any ideas how/why this works or why, in comparison, having a fairing directly behind the wheels may prove better aerodynamically?

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Old 09-19-2017, 01:11 PM   #2 (permalink)
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I suppose it could depend on what you are trying to achieve. If you are trying to direct airflow for speed and stability then that may require different parameters that trying to achieve efficiency.
The additions to the roof of this UK Stock Car (I know, different definition here)



would do very little on your street car, regarding fuel consumption.
It is a case of "horses for courses".
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Old 09-19-2017, 01:16 PM   #3 (permalink)
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Sure, but that stock car roof/spoiler seems obviously poised to achieve downforce/stability at the expense of efficiency, just like any other kind of spoiler. Even the airflow image above of the open wheel well seems to show air from the wheel well being directed straight backward and not up to induce downforce, for example.

How would leaving the back of wheel wells open do that or be applied for any reason other than efficiency?
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Old 09-19-2017, 01:33 PM   #4 (permalink)
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All that I do is suggest you look at the original Honda Insight, although they changed this for later years:
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Old 09-19-2017, 03:28 PM   #5 (permalink)
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The opening article hits on one of the topics we have mulled over before.

Quote:
I guess you want to know more on the aerodynamics side though? For that, I would say that I learned the most about pitch sensitivity, which is the way the aero changes when the car brakes and accelerates. Every car suffers from that
The car on the track is constantly braking and acclerating, often in turns and at various inclines/declines. Much more aggresive than a car on the street or hwy.

What works great cruising at 70 mph to and from work isn't what the track demands and vice versa.

That said, I suspect with so many track variables and rule restrictions, they are bound and gagged from doing what we might do.

One can often tell when a true aerodynamic designer/engineer is employeed by a race team, the cars start looking girly.

I think many race cars suffer from a knicklehead viewpoint, avoiding the more artistic solutions avaliable. The ones brave enough to cast away preconceptions and fear make the disruptive game changers. Then they are copied or get banned by rules to level the playing field.

This is the history of racing.
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Old 09-19-2017, 06:37 PM   #6 (permalink)
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Quote:
I think many race cars suffer from a knicklehead viewpoint
It will always be knucklehead for me.




I'd like to see this treatment on a VW Beetle with the front axle pushed out 8 inches so the footwell comes to a point.
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Old 09-20-2017, 05:53 PM   #7 (permalink)
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Quote:
Originally Posted by mikesheiman View Post
Was reading an article on A Brilliant View Into Aerodynamics - Speedhunters.

It struck me as odd and possibly contradictory that the images actually seem to recommend having an open area right behind the tire (virtually no fairing), as opposed to a fairing directly behind it gradually sloping inwards. Even though, obviously, those designs still push/keep air away from the front and sides of the tires.

Any ideas how/why this works or why, in comparison, having a fairing directly behind the wheels may prove better aerodynamically?
Interesting article. Thanks for the link. In the examples above, these cars are designed for huge downforce and tire grip which is often contradictory to low drag aerodynamics for better mpg. We hypermilers tend to drive at lower speeds with skinny tires tucked inside the bodywork. To answer your question, this works for this race car designer because it helps generate downforce. Exposed wheels will not help with a low drag design. Look to solar racers and salt flats streamliners to see cars designed for low drag aerodynamics.
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Old 09-20-2017, 06:26 PM   #8 (permalink)
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It lets the smoke out.

Edit:
Quote:
...salt flats streamliners...
Here's what Luigi Colani took to The Salt.



A radical example of spatted wheels. IIRC the shape was based on the Gerridae aka Water Strider.

Last edited by freebeard; 09-20-2017 at 06:39 PM..
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Old 09-20-2017, 06:32 PM   #9 (permalink)
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I believe they are trying to vent air pressure from under the car to create a low pressure area with a rear diffuser to suck the car down to the road.
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Last edited by COcyclist; 09-20-2017 at 06:36 PM.. Reason: double post
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Old 09-21-2017, 03:03 AM   #10 (permalink)
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Quote:
Originally Posted by COcyclist View Post
to suck the car down to the road.
I wouldn't imagine that would be an aid to fuel efficiency.

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