Matt,
I agree that if the car is tracked, you want to address front-end lift. Just because it is not extreme until 190 MPH doesn't mean it isn't happening at lower speeds. If a car has lift, it has lift at all speeds. You won't notice as much of a change at 150 MPH as you would at 190 MPH, but you will still have some downforce instead of lift if you make the changes. This can show up as better balance in cornering, which people frequently don’t attribute to the addition of downforce, because the old lift situation wasn’t drastic and so they didn’t realize how much it was throwing the cornering balance off. This is one of the advantages of the adjustable rear spoiler. It gives you the ability to tune high speed cornering behavior by adjusting the height.
A flat under tray will help with drag, but won’t do a lot for downforce unless the car is equipped with diffuser tunnels (In which case it is mandatory). If you have a tube frame car, an under tray will clean up the airflow (although at a cost of extra weight for the aluminum sheet). If you have a monocoque car, you already have a smooth underbody.
As for cutting an aperture to vent air, it would be too late. The high-pressure air would still be present under the first several feet of the nose and would cause significant lift before it got to the vent. You need to keep the air from ever getting under there to begin with.
Kevin
I agree that if the car is tracked, you want to address front-end lift. Just because it is not extreme until 190 MPH doesn't mean it isn't happening at lower speeds. If a car has lift, it has lift at all speeds. You won't notice as much of a change at 150 MPH as you would at 190 MPH, but you will still have some downforce instead of lift if you make the changes. This can show up as better balance in cornering, which people frequently don’t attribute to the addition of downforce, because the old lift situation wasn’t drastic and so they didn’t realize how much it was throwing the cornering balance off. This is one of the advantages of the adjustable rear spoiler. It gives you the ability to tune high speed cornering behavior by adjusting the height.
A flat under tray will help with drag, but won’t do a lot for downforce unless the car is equipped with diffuser tunnels (In which case it is mandatory). If you have a tube frame car, an under tray will clean up the airflow (although at a cost of extra weight for the aluminum sheet). If you have a monocoque car, you already have a smooth underbody.
As for cutting an aperture to vent air, it would be too late. The high-pressure air would still be present under the first several feet of the nose and would cause significant lift before it got to the vent. You need to keep the air from ever getting under there to begin with.
Kevin