I have an FD with 255/45R16 and I need to know what tire preasure I should run for the 1/8th mile drag. how low should I go?

 

if they're street tires go with the manufacturers rating. if they're underpressured you'll put to much stress on the walls, and overinflated will cause you to not hookup.

 

I probably wouldn't go below 20 psi or so on regular street tires. The literature for my BFG g-force drag radials says never go below 12 psi, but I've never run them that low. It hooks up pretty good in the mid-20's.