Yamaha YFM225S 1985 Owner's Manual page 37

How to measure tire pressure
Use an appropriate low-pressure tire gauge.
Set tire pressures to the following specifica-
tions:
Reference tire pressure:
19.6 kPa (0.20 kg/cm
2 ,
2.8 psi)
Min, tire pressure:
16.6 kPa (0.17 kg/cm
2 ,
2.4 psi)
Never use a tire pressure below minimum
specification. The tire could separate from
the wheel under severe operating conditions.
NOTE:~~~~~~~~~~~~~
An optional low-pressure tire gauge is
available. Please ask your nearby Yamaha
dealer.
-30-
Tire wear limit
When the tire groove decreases to 3 mm (0.12
in) due to wear, replace the tire.