If you are only doing 100 mph in the 1/4, I would keep the pressure on the high side (like between 15-20 psi). You won't be spinning unless the track prep is atrocious. To answer your other question, I ran my Hoosier QTP's at 13.5 psi. I have run them as low as 11 psi, but the car did the "slick shake" on the big end of the track pretty bad....not fun. I run Hoosier drag radials now at 19 psi...VERY stable at high speed, and still run the same ET as I did with the QTP's.
