Honda TRX500FM6 Owner's Manual page 194

Wheels & Tyres
Also, if you hit a pothole or other hard object while riding, stop as
soon as you safely can and carefully inspect the tyres for damage.
Tread Wear
You must periodically confirm the tread wear depth.
NEW
(2)
(1)
4 mm
(0.16 in)
(1) groove depth
(2) wear indicator
To check the condition of a tyre tread, measure the groove depth (1)
in the centre of the tyre, or check the wear indicator (2).
For best performance, you should replace a tyre before the tread
depth at the centre reaches the following limits:
front
rear
184 Servicing Your Honda
Replace
(3) wear indicator
4 mm (0.16 in)
4 mm (0.16 in)
location mark
(3)