Another Aerodynamic question

[Beostar]

EDIT by Tomba: for people who can't see the pic, follow this link:
http://www.amazingcars.freewebsites.com ... e956c1.jpg

If you look at that car you see that it has a filled wheel. a bit like cycling bikes during a time trial.

I was wondering why it was? I've seen it on the ABT audi during the DTM race @ Nurburgring but I can't seem to find out why?

Anyone got any ideas?

[akbar21881]

can't see the pic. but i guess it may be a flat wheelcover. it is used to prevent the air from circulating from outside of the wheel to inside of the wheel and vice versa. this can create turbulence and therefore less aerodynamically efficient.

i've read in autocar about the effect of wheel design on top speed of the car. i can't remember what car it is,but it is one of GM car. in windtunnel,using flat cover for wheel top speed is something like 150.but in production trim with "stylish" sport rim, top speed was reduced by as much as 10 mph. rim spoke can act like blade,pushing air in/out of the wheel and disturb the airflow surround the car.

[Monstrobolaxa]

Well......simple the answer to this question.....air tends to flow from lower pressure areas to higher pressure areas....to simplify things.....from slaower air to faster air.....

When the car is moving the air that circulates around the car circulates faster then in the brake ducts...and wheel bearing area....so the air tends to be sucked out from inside the rim....this is quite good actually for brake cooling......but has a negative side.....the difference between air speeds tends to create turbulence (one of the ways to create turbulance)....which willl have a negative efect on the handling of the car....

What those rim covers do is seal the rim preventing the slower air from "exiting"! this way reducing drag!

[Monstrobolaxa]

Small corection to my previous post....air tends to flow from high pressures to low pressures....and not low to high.........the rest is correct.......slow to fast....

[Steven]

hmm not sure here.. but would that not hinder the cooling of brakes a little?
At least in F1 air is sucked onto the brake discs from between the wheels, and gets away at the outside, with of course all the carbon dust (which is why wheels are dirty so fast in F1).

Or do GT's have watercooled brakes?

[joseff]

I remember back in mid-90s BTCC, cars have those dish covers at the back wheels only. Those were actually there to keep the brake temp high. Don't know if they're still there... is the BTCC still running anyways?

So it was an effort to eliminate the temperature difference between the front & rear brakes. Anyhow I'm *quite* sure GT cars are fast enough to keep the rear brakes toasty... so I'll take the drag reduction explanation for the Porsche.

Also, the '94 (6-cyl) BMW M5 came with 17" wheels and those (evil of all evils!) wheel covers as standard. The owner has the option to keep them on, which makes the tires look like tall whitewalls (eek!) or take them off.

[Monstrobolaxa]

yup....on the Porshe it seems to me that the covers are there for aerodynamic reasons....cause if you look closly at the pic it seems to me that the brake ducts are underneeth the the lights.....(don't think they are radiator ducts....they're just too small...)....

joseff...you mentioned the BTCC using them at the rear to keep the brake temp up.....never heard of that but it's true....(thinking about it)....in the late 80's early 90's they used those covers at the INDY 500.....in this case I believe they had double purpose.....aerodynamic....and mantaining the little heat that the brakes gather during braking at Indy....cause....they don't brake too much at Indy...