Honda 2012 TRX420TM Owner's Manual page 166

Tires
Also, if you hit a pothole or other hard object while riding, stop as soon
as you safely can and carefully inspect the tires for damage.
Tread Wear
FRONT
NEW
(2)
REAR
Replace
NEW
(1) groove depth
(2) wear indicator
To check the condition of a tire tread, measure the groove depth ( ) in
the center of the tire, or check the wear indicator ( ).
For best performance, you should replace a tire before the tread depth at
the center reaches the following limits:
front
rear
158 Servicing Your Honda
Replace
3/16 in
(4 mm)
(1)
3/16 in
(4 mm)
(3) wear indicator
location mark
3/16 in (4 mm)
3/16 in (4 mm)
(3)
1
2