Honda 2012 TRX420TM Owner's Manual page 163

Tires
Air Pressure
Refer to Saf ety Precautions on page 89 .
Properly inflated tires provide the best combination of handling, tread
life, and riding comfort. Generally, underinflated tires wear unevenly,
adversely affect handling, and are more likely to fail from being
overheated. Overinflated tires make your ATV ride harshly, are more
prone to damage from surface hazards, and wear unevenly.
Make sure the air valve caps are secure. If necessary, install new caps.
Servicing Your Honda 155