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Vancouver Auto Chat 2016 VAC Community Head Moderator: Raid3n

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Old 03-23-2017, 10:01 AM   #1
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fluid dynamics experts needed. less drag with spoiler...what?

So I was poking around on subaru.ca checking measurements and trying to figure out if my new car will fit in a parking spot at work and noticed something really odd. (I know somebody will make a comment...yes, before I bought the car I checked to see if it wouldl fit in my current spot but I've scoped out a new spot that is smaller but in a better location that I wanted to see if I could get)

For the WRX Base(completely spoilerless), WRX Sport/Sport-Tech(trunk lip) and STI Base(trunk lip) the CD is 0.34 but on the STI Sport/Sport-Tech the CD is 0.32

To me this is counter intuitive seeing as this spoiler is supposed to be functional at a certain speed. Even if the spoiler isn't making any downforce at lower speeds shouldn't it still create more drag?

Doesn't this mean that a WRX with an STI Spoiler would actually benefit from better fuel efficiency(all things being equal) and having functional downforce at speed?

Is this common or has subaru found a sweet spot in their wind tunnel testing where at that specific airspeed this anomaly occurs?

If you want to see what I was looking at go to the link below and then click on "Measures"

2017 WRX/STI Specs
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Old 03-23-2017, 10:41 AM   #2
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Originally Posted by Indy View Post
For the WRX Base(completely spoilerless), WRX Sport/Sport-Tech(trunk lip) and STI Base(trunk lip) the CD is 0.34 but on the STI Sport/Sport-Tech the CD is 0.32
When I click on measurements, the base STi has a 0.32 CD.
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Old 03-23-2017, 10:54 AM   #3
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When I click on measurements, the base STi has a 0.32 CD.
haha damnit I went to check it like 3 times before I posted. ugh.

so I guess it's something up front that's changing the numbers although I thought everything body wise was the same.



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Old 03-25-2017, 11:06 AM   #4
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Originally Posted by Indy View Post
So I was poking around on subaru.ca checking measurements and trying to figure out if my new car will fit in a parking spot at work and noticed something really odd. (I know somebody will make a comment...yes, before I bought the car I checked to see if it wouldl fit in my current spot but I've scoped out a new spot that is smaller but in a better location that I wanted to see if I could get)

For the WRX Base(completely spoilerless), WRX Sport/Sport-Tech(trunk lip) and STI Base(trunk lip) the CD is 0.34 but on the STI Sport/Sport-Tech the CD is 0.32

To me this is counter intuitive seeing as this spoiler is supposed to be functional at a certain speed. Even if the spoiler isn't making any downforce at lower speeds shouldn't it still create more drag?

Doesn't this mean that a WRX with an STI Spoiler would actually benefit from better fuel efficiency(all things being equal) and having functional downforce at speed?

Is this common or has subaru found a sweet spot in their wind tunnel testing where at that specific airspeed this anomaly occurs?

If you want to see what I was looking at go to the link below and then click on "Measures"

2017 WRX/STI Specs
Drag and downforce aren't directly proportionate. An aerodynamically efficient design is meant to create downforce with as little drag as possible

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Old 03-25-2017, 12:32 PM   #5
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Some spoilers are very well engineered that they will increase the downforce and decrease the drag.

I have seen such spoilers from TRD, Mazdaspeed, Mugen, etc.
If you add spoiler, it changes the airflow of the back of the car.

My amateur guess is that it changes the slipstream so that low pressure air isn't dragging the car backwards anymore.

As you can see, these vehicles create a lot of drag



Solar cars like Nissan Sun Favor, Toyota Rara10, Honda Dream had drag coefficient of 0.10 to 0.11



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Old 03-25-2017, 04:49 PM   #6
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Won't the top trim level have more features = more weight, which should make the car sit a hair lower (since I assume the suspension is the same)?
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Old 03-25-2017, 06:22 PM   #7
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Some spoilers reduce lift and do nothing for downforce. They can also decrease drag. Its very specific to each application.
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