Honda FourTrax Rancher TRX420TM1 2019 Owner's Manual page 181

Tires
Air Pressure
Refer to Safety Precautions on page 101.
Properly inflated tires provide the best combination of handling,
tread life, and riding comfort. Generally, under inflated 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 171