As to the shape of the Crossfire without any kind of wing or spoiler. Just look at my signature and imagine the wing is gone. Now... look at the only parts of the car that create downforce... the front windshield is about it... then as the air travels over the car it begins to create a low pressure area behind the car as it tumbles down the rear hatch area. This low pressure area creates lift on the rear half of the vehicle. Now the other 'lift' comes from the front of the nose splitting the air. Mostly it's vertical then swooping back at the top of the nose, so not much lift there. It forces the air around the front of the nose or up and over creating some downforce.

The rear of a Crossfire also has diffusers on either side of the exhaust pipe exit area. You can buy an accessory that bolts on that has fins in this area to help straighten the air as it's exiting from under the vehicle. This area creates downforce by using the low pressure area behind the vehicle to suck air out from under it, thereby transferring the low pressure area to under the car where it will pull the car down.

Crossfires (unaltered) will 'settle' in at just over 75 mph and begin to sink ever so slightly and stabilize. Without the wing (Active or fixed) in the rear, this would not happen so easily and will actually begin to get worse the faster you go.

If you're all about style and don't want a wing and NEVER plan on driving more than 65 or 70 in a straight line (big interstate)... then be my guest to remove your spoiler/wing. If you DO plan on driving over 75 on even straight roads... don't be surprised if the car begins to want to 'dance' a bit in the rear when you do so without a spoiler/wing.

I can actually feel it when the car hunkers down and powers though a turn at over 90 mph. Stable and strong on street tires that aren't even beginning to complain.

That's my story and I'm sticking to it... (But the hammock is still in the attic).