It appears that my favorite bass truss rod is maxxed out.

I've been using extra light Hartke nickels and deicided to try the lightest flats I could find. Unfortunately the neck won't handle those at all. So I'm looking for the lightest tension strings to allow the neck to get proper relief.
The Hartkes almost had it, but the neck still had a bit too much forward bow.
So, is there a net site that might have comparitive string tension in lbs or metric, or should I be just looking for the smallest diameters? TIA