I would start with 8 psi ! That's way to low for that big a tire ! I agree that the front end is to high, I had an old DC spoiler on our Duster, It was always stable on the top end ! But when the car was on the edge of a 9 second pass I just couldn't get it there, my pops suggested taking it off ! I didn't really want to, I thought I would upset the car, but did ! Next pass the car went 9.93 with no other changes ? Where running 10.05 10.06 and 10.04 ! The car drove the same as it did with it so I stuck it up in the barn and haven't had it on since !