In land speed stuff its not really for downforce it just to keep air out from under the car. A real land speed car wants little downforce as possible. The more downforce the more power it robs to push the car. That is why most speed cars are heavy tanks. My buddy's Bonneville car that goes 320 MPH weighs 5200 lbs and has such little down force it only compresses the shocks 1/2 inch at that speed. I think it has different affects and outcomes in dragracing.