Tire Wind Deflector Question

[Otto]

Originally Posted by skyl4rk

Thats new to me. Why does the air flow in an angle, if the car is going straight? Pressure from the front end of the car moving to the outside?

Bow wave off the nose flows laterally around the front of the car, and if unfaired, the front wheels act as a flow fence impeding the bow wave, creating drag.

The oblique angle is greater than I would have thought, until studying a photo in the Hucho book, showing a smoke stream around the front of a Calibra (I think). In that pic, the smoke stream angled about 60 degrees outboard from centerline. Maybe somebody with Hucho who can post pics can find and post it here for us.

For your car, tuft testing would be cheap and easy. Perhaps the tufts could be mounted on inverted Ts 2-4" under the nose, so visualize flow several inches below the body, as the air moves rear toward and around the front wheels. Then, set the incidence of the deflectors accordingly.

[fusion210]

I came across a newer BMW 325i in a parking lot, thought of this thread and snapped a couple pictures.

They look to be designed like this.


http://i42.tinypic.com/2lih6jr.jpg
http://i40.tinypic.com/8ydpus.jpg


Maybe they also block air from the front suspension?

[aerohead]

The GM Sunraycer scored Cd 0.088 in the windtunnel and Cd 0.12 in full-scale race trim.The car originally had fairings fore and aft of the tire/wheels.That car was prone to lift,and when the nose took off,the area of the wheel fairings acted to turn the car sideways,which would dis-qualify it for competition when exposed to gusts from triple-trailer trucks in Australia.------------ Later,HONDA,with their Dream-2 Solar car,included the wheel fairings and the Drag coefficient fell to Cd 0.10.So the fairings can make a measurable difference.If your going to spend time messing around with this sort of thing I would encourage you to look at the Dream-2 and use it as your model,or Ford's Probe-IV concept car.-------- The flat panel as you see employed on contemporary cars has a drag coefficient of Cd 1.11 in free-air,and unless carefully sized in a windtunnel,as others have mentioned,you could easily oversize them,shooting yourself in the foot in the process.

[cfg83]

alohaspirit -

Thanks for this thread. I think my "reverse mudflap" configuration has been in error all this time. Based on all this info I think I need to adjust my "straight down" horizontal mudflaps to look more like the OEM ones on production cars :



What you don't see in this front view is that they are straight down. I think I also need to either angle them a bit and/or create a sloped frontal edge to help the air transition better.

CarloSW2

[Geo Metropolis]

Originally Posted by skyl4rk

Behind the tire, make a long trailing edge that comes to a point. In front of the tire, either do nothing, or put a small rounded deflector that approximates the curve of a naca foil.

Between the front and rear tires, you can put in a catamaran which is a box between the wheels.

What you've described here is basically what Aerocivic has done here: he has deflectors in front of the tires, long parallel channels (like double sideskirts) running the distance between front and back tires along the outer and inner edge of the tires, and a mini boat tail shape after the rear tire.

This whole thread has been really informative for me as I consider what's best for my metro which already has a full bellypan.

I'm willing to build catamarans but I think doing the airfoil shape before and after front AND rear wheels like suggested in Post 11 (I imagine I should only angle the foil for the front wheels as air is traveling more head on by the rear wheels?) would might prove effective and would allow for better clearance of driveways and the like.

What do you guys think?