Honda 2012 TRX420TM Owner's Manual page 164

Tires
Always check air pressure when your tires are ''cold.'' If you check air
pressure when your tires are ''warm'' even if your ATV has only been
ridden for a few miles the readings will be higher. If you let air out of
warm tires to match the recommended cold tire pressures, the tires will
be underinflated. Be sure to check tire pressure at the riding site, since
changes in altitude can affect air pressure.
The recommended ''cold'' tire pressures are:
(TRX420TM/FM)
RECOMMENDED
PRESSURE
(TRX420FPM)
RECOMMENDED
PRESSURE
156 Servicing Your Honda
FRONT
3.6 psi (25.0 kPa) 3.6 psi (25.0 kPa)
FRONT
4.4 psi (30.0 kPa) 3.6 psi (25.0 kPa)
REAR
REAR