Honda TRX420TM Owner's Manual page 161

Tyres
Air Pressure
Refer to Saf ety Precautions on page 89 .
Properly inflated tyres provide the best combination of handling, tread
life, and riding comfort. Generally, underinflated tyres wear unevenly,
adversely affect handling, and are more likely to fail from being
overheated. Overinflated tyres 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
151