I have seen lots of pics of different kinds so I wanted do do a poll on them.

A
Tire
|/ ---outside
Front of Car

B
Tire
\/ ---outside
Front of Car


Which of the two shapes better to have in front of the tire? I was thinking A because it doesn't create higher pressure between the wheels.

I was further unsure if I should ramp it down or just have it be a wedge.

Than my last thought was behind it make a 'boat tail', /\, behind it angled up to return the air to the body.

I'm having a little trouble deciphering the ASCII characters. Perhaps you could indulge us with a picture or sketch?

hope this helps to make sense.

If I understand your pictures correctly, it appears as if you have two styles of diffuser/spoiler thingees. Seen from above, one splits closer to the center of the car, while the other splits at the centerpoint of the tire.
Did I get that right ?

If so, my guess would be that drag reduction would depend on the suspension pieces around the tire. 'B' would tend to send more air to the sides of the car, while 'A' would split it equally .

If the underside of the car is smooth and the suspension pieces don't hang down much, it still might be beneficial to send the air around the sides of the car.
I'll let the experts answer. What do you say guys ?

Try using tell-tales to detect the current air flow around the tires, and put the center of the fairings paralell to that.

Here is a really good 2 part series on this from autospeed.com:

Modifying Under-Car Airflow Part 1

Modifying Under-Car Airflow Part 2

snydertalon -

I voted "A", but that was a gut-intuition thing.

CarloSW2

my hillbilly know how says A.

splitting into undercarriage where there is an engine exploding under control needs some room before anything gets to it. in front of the tires is a good place to start a wake, and not pretend the engine isn't exploding under control, explosively expanding all the time, explosively powerfully unknowable...bomb like explosively explosive.:confused:

just some thoughts:

keep in mind that directing air to the inside will direct it inside the inner wheelwell. a good deal of dans seem to be aimed at keeping air out of the well so with that in mind directing everything outside could be a good option.

also note that the part of the wheel that touches the ground isn't moving relative to the ground or the air
(the car is moving trough the air the air just it's there)!
so it could be beneficial to direct some air the the lower tire surface, as the forward speed of the tire surface will decrease relative to the axle.
it's quite logic but it can be confusing,
think of a tanktrack for example, where the tanktrack is layed out in front of the tank on the ground.
the tank moves over it, and than picks up the track, transports it at twise the speed of the tank back to the front and so on. a tank track is basically a very flat tire. so the frontal motion relative to the air decreases. the air is pushed asside though, but rather by rolling over it than by pushing it asside....

this means that rather than directing all the air left and right, directing some down could be a good idea wich would explain why a lot of wheel dams are flat rather than wedge shaped.