How do you control the position of the back flying lines on the bar? Usually, a 45 cm bar is used with kites surfaces from 5 to 9 m2, 50 cm bars are used for 10 to 12 m2 kites, 55 cm bars are more suited for 12-15 m2 kites and 60 cm bars are used for kites above 15 m2. This depends on the kite brand and how fast you want the kite to turn too.