The Rider's Handbook
Selecting a safe gap when turning, overtaking or changing lanes is a critical skill to safe riding. Gap selection is also very important at intersections where the chance of colliding with another vehicle is very high if the gap you select is too small.
A safe gap is one that enables you to turn, overtake, change lanes or cross an intersection without affecting the crash avoidance space of other road users.
A safe gap ensures that other vehicles do not need to change their speed or position. When turning across traffic make sure your vehicle is clear of the intersection by at least three seconds before the approaching vehicles arrive. When joining a traffic stream select a gap that allows you to reach the traffic speed before the approaching vehicles are within three seconds of your motorcycle.
Overtaking other vehicles is very hazardous. You not only need to be able to judge the gap between your motorcycle and an oncoming vehicle, you also need to have enough space between your motorcycle and the vehicle you are overtaking.
When overtaking maintain a buffer zone between your motorcycle and the vehicle you are overtaking. On country roads and highways there are often overtaking lanes at regular intervals that allow you to safely overtake.
Before overtaking, do a head check to make sure that someone isn't trying to overtake you.