to those with a 4" or more front drop... wheel/tire question

[miller6t9]

so....I had 235/70/15 on 15x8.5 TTO with -24 offset on my '72 that has CPP 2.5" drop spindles and some sort of not stock but lowered somehow springs....bought 255/50/18 tires for the 18x8 TT 2 -18 offset that i was gonna put on after the body work but tested them out for a few days and rode/fit fine...no issues....changed the front springs to the Hotchkis 2" drop and rode on the 15s for about a year with no issues...now i have the body work and all done on the truck and have a rubbing issue with the 18s...have done way too much searching and reading and whatever, but still unsure....do those of you with a 4 inch drop run a 255 tire? (really not wanting to buy two new tires) Would a change to the zero offset probably solve my problem? what kind of offset do those of you with a similar drop run?...now the rub I'm getting is only on bumps or dips occasionally, is this something you all deal with anyway?