rubber many times over for increased traction. When airing your tires you don't want to go too deep and risk breaking a bead, so precision is important. I have a friend who owns his own shop who has a calibrated pressure gauge and it has always been within 1 PSI of his gauge at lower pressures (15-20 PSI) but not as accurate at higher pressures (35-40 PSI). ranged from 2 to 3 psi. The Rhino 150 psi digital tire pressure gauge was accurate to within 1 psi and ranged from 15 to 45 psi.