[kamesama980]

as a former tire shop employee (one of the few that went to school rather than doing it for lack of finding other work) the bulge you see has little or nothing to do with inflation, it's physical damage as one of the earlier posters mentioned having to do with the belts. replace the tire ASAP and don't underinflate it to bandaid the problem, it won't last much longer at any pressure. in this case it's largely due to the age of the tire but can also be caused by road surface issues (aka running sh** over) or suspension problems (worn struts/shocks, ball joints, bushings, etc)

some congrats on getting that many miles out of the tire but that's like saying your car ticked over 200k miles. while many people manage to run their car into the ground by then, a maintained car can do it well.