What is the ideal tire pressure for Suzuki GN250?

This is what the manual suggests

Solo Riding

Front 175 kPa, 1.75 kgf/cm2, 25psi

Rear 200 kPa, 2.00 kgf/cm2, 29psi

Dual Riding

Front 175 kPa, 1.75 kgf/cm2, 25psi

Rear 225 kPa, 2.25 kgf/cm2, 33psi

This is what I do for my GN250 (I weigh 100 KG):

Solo Riding

Front 175 kPa, 1.75 kgf/cm2, 27psi

Rear 200 kPa, 2.00 kgf/cm2, 32psi

More air in your tyres means less contact with the ground, which means more speed, less fuel but reduces your braking ability by about 7%. If you are a good confident rider, and you ride safe, you should be fine using my settings also have your weight in mind.