Chassis changes for topless wing and spoiler addition.

[dirtrace09]

You can use Bernoulli's principle to your advantage for downforce with a roof (and you don't have to dish it). Take it off and you have eliminated a large portion of that downforce.

[Matt49]

My belief (and it could be wrong) is that the roof creates more turbulence than we might think which keeps clean air from getting to the rear deck and spoiler. Meaning that the net affect of the roof is actually less down force. The fact that a lot of the newer roofs have vortex generators on the back of them would be an indication that someone besides me believes that too.
My belief is also that a spoiler on a late model is not as much of a spoiler in the traditional sense and really is more of a wickerbill (Gurney flap for you old timers) for the larger air foil which is the nose and deck of the car. And the fact that I see people running their "spoiler" at 90 degrees to the deck tells me I'm not alone in that line of thinking.
Fun stuff to think about.

[billetbirdcage]

My belief (and it could be wrong) is that the roof creates more turbulence than we might think which keeps clean air from getting to the rear deck and spoiler. Meaning that the net affect of the roof is actually less down force. The fact that a lot of the newer roofs have vortex generators on the back of them would be an indication that someone besides me believes that too.
My belief is also that a spoiler on a late model is not as much of a spoiler in the traditional sense and really is more of a wickerbill (Gurney flap for you old timers) for the larger air foil which is the nose and deck of the car. And the fact that I see people running their "spoiler" at 90 degrees to the deck tells me I'm not alone in that line of thinking.
Fun stuff to think about.

Wind tunnel data seems to back that up, but like everything it varies and overall height of the cage/roof is gonna come into play, I'd assume you could get the roof high enough that it might not effect the deck as much and still use as a wing but probably be way over the legal limit at that point. That's a guess on my part.

[rick james]

It is a limited late deal. Billet you are correct on the wings and spoiler. Car has a tendency to push when track is tacky when entering too hard. I suspect this is caused by right front over traveling, because driver can back entry up a little and problem goes away. Do you think this problem will be worse? Or will the extra pressure on left rear from wing offset the extra force put on right front? Car is money at feature time.