Tire Pressures

I just got back from Test/Tune this weekend. I was trying to dial in my new Caltrac bars. I started at 16 psi went as low as 12psi and back up to 18psi I ran the same 60 foot at all settings. so I will stick in the 18 psi range. I am running MT ET streets with tubes. I was a little disapointed that I couldnt get more out of my 60 foot time but the track was hot and I think I will now need to go with new rear shocks.