A longer bar gives you a bigger differential between your back lines when turning, resulting in a bigger input into the kite. i.e. faster or more responsive turning. And therefore a shorter bar gives less differential and results in a smaller input into your kite. i.e. slightly slower or less responsive steering. It's great for having one bar set up for all sizes of kite. you can just shorten your bar on the small ones or on super windy days.
