Car & Driver Aerodynamics Test

[aerohead]

Originally Posted by Vman455

Looks like Mercedes opened its own aeroacoustic tunnel last year; buried in the press release is a reference to a climate tunnel opening two years before that.

https://www.daimler.com/dccom/0-5-71...0-0-0-0-0.html

Thanks Vman455,this helps a lot.And would explain the photos of ice-covered M-Bs that are out there.
It would be nice if Daimler had published an SAE paper discussing the merits of the spinning wheels.
Ferdinand Porsche would drive 90-mph between Stuttgart and Berlin on the Autobahn in the 60K10,with fully covered wheels.Brake cooling didn't seem to be an issue.
With the climatic tunnel,they could simulate brake loads and evaluate brake cooling performance.
I've driven the Autobahn only once,but on the unlimited speed sections you'll see the large Benz, BMWs,and Porsches blow by at top speed.You wouldn't want brake fade out there in a panic stop situation.The ceramic rotors must be great!

[aerohead]

Originally Posted by oldtamiyaphile

VW quote 0.33 for the T5 Transporter:



I coast down tested my old MB100 and after running the numbers it came out to 0.36, and given the VW's vastly better coasting (basically identical frontal areas), I have no problem believing VW's 0.33 claim. Now given that a brick can be aerodynamic, I see no issue with 0.26 for a GT-R.

The Cds for the vans don't seem out of line a bit.FIAT has had a bus with around Cd 0.28 for a couple of decades.Here's some examples:

[aerohead]

Originally Posted by UltArc

It was clear, now it is not clear lol. Does anyone have resources I could review to expand my knowledge on this? I understand how a wing is going to hit the air and become an issue, but if it's creating less force than the underbody (which has less drag) wouldn't it noticeably increase the rolling resistance? I suppose RR should not be included in Cd lol

We ought to select one vehicle and consider it with different configurations.
I have an SAE paper on Indycar aerodynamics from awhile back which included the wing research.
*The body was around Cd 0.28
*Adding exposed wheels netted around Cd 0.56
*Adding front and rear wings pushed the drag over Cd 1.0
--------------------------------------------------------------------------
*At rest,the car weighed 1,400-lbs
*At race velocity the car weighed 5,500-lbs
-------------------------------------------------------------------------
*You can imagine what the rolling resistance would do,but this downforce allowed the car to carry 235-mph through the curves.
------------------------------------------------------------------------
*The diffuser is a ground proximity device.Depending upon where the diffuser starts on the body,it can be optimized for low drag at shallow angles.
*With steeper angles,the diffuser triggers separation and allows the low base pressure of the wake to migrate under the car's rear,as far forward as the length of the diffuser.The low pressure acting on the underside of the diffuser creates a moment arm( torque) which attempts to pitch the car, rotate it around the rear axle,lifting the nose,creating downforce,which is balanced (hopefully) by the weight bias of the car.
*This 'torque' can be 'tuned' by varying the diffuser angle.
*And I agree that there bis probably a 'sweet-spot' at which you get drag reduction as well as a little downforce.
*If you drive at extra-legal speed and hit a wet spot,this extra downforce might mean the difference between hydroplaning or not.

[gone-ot]

As Arsenio Hall would say with a British-accent: "...it's all about the BOOTIE..." (wink,wink)