Someone car to explain this statement about the JGTC undertay to me?

[khappucino]

For 2003, a ruling that has been enforced for a number of years in the Le Mans and FIA regulations makes it way into the JGTC. Between the centerlines of the front and rear wheels of the car, the underbody must be fitted with a flat bottom. As a result, the down force of the car is affected remarkably. "My first impression of the car during the shakedown was... 'My goodness. What's that feeling? There's a bit less down force, I wonder?'" commented Daisuke Ito after driving the No.16 NSX entered by Mugen. "If we set the rear wing-angle to that of last year, there is entirely too little grip. There has been a tremendous reduction in down force."

so... which surface exactly are they talking about? i just got a little confused as it seems that we ususally put diffusers under the car to reduce turbulant airflow, unless they are talking about some esoteric undercarriage shaping to maximize downforce?

 

[Dave Hardy]

They are being forced to reduce the difuser from one that likely starts somewhere around the A Pillars to one that starts at the rear axle centerline.

 

[Ponyboy]

I think they're talking about the underside of the car and its shape. As far as I understand, to achieve maximum downforce (or suction) the underbody is typically not flat all the way from front to back. There's an elevation and then return to flatness in the front and rear section. Crude example...


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Interesting question...

 

[fkong777]

I think the JGTC rule that the underbody must be FLAT.. cannot have venturi tunnels under the car to create more down force.