Quote:
Originally Posted by serialk11r
Thanks for the insight.
Why would you want to cover the center with a partial cover though? I can't wrap my head around this...Aren't the spokes moving faster at the edge of the rim?
On the same note, I noticed that some cars have the wheels flush to the side of the car, but others (such as my car, and other Toyotas from the same time period) have the fender poking out more at the top of the wheel and receding towards the bottom, would this possibly "isolate" the air being churned by the wheels better?
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The inner face of the rim provides a duct 'wall' which is in the area unobstructed by the rotor and hub.Tranverse flow can move as freely as possible,through the spokes and out.
If you sealed this area and opened the center,you'd be asking the air to make a right-angled turn past a Cd 1.11 flat plate(rotor) within the wheel and flow towards and through an equally 'draggy'
vena contracta.
Here is a Borda tube with the vena contracta (in yellow).You can see how the flow is choked off even though it's an 'open' hole.
It's a torture chamber as far as airflow goes.
If you keep the flow near the rim you have more interior space to provide some radii inside the cover to kill the vena contracta with.Think of an inside-out velocity stack/outside curve of a donut inside the cover.
This internal drag far outweighs any penalty due to the spokes.