I will also chime in that 30psi is ridiculously high for 4" tires.

My Surly Krampus wears 3" wide tires, I'm a fatso at 250lb, and I consider 10 psi front / 15 psi rear to be pumping them up extra high. 8/12 is probably ideal.

Get the fattest person you can find and have them bounce up a standard sidewalk curb. Lower the pressure gradually and repeat. When they finally touch the rim, add a few psi back and use that.