Size 110/90-16 tires
From Ninja250Wiki
REGARDLESS OF TIRE MANUFACTURER, YOU MUST RAISE THE FRONT FENDER IF YOU ARE INSTALLING A 110/90-16 FRONT TIRE. You don't want BAD THINGS to happen.
This is especially applicable to Dunlop GT501 tires, as Dunlop doesn't sell size 100/90-16 in the US. Other manufacturers generally have the smaller size available, and you would be better off going with the 100/90-16 in that case (such as Sport Demons).