What is the 'two-second rule' for motorcycle following distance?

The two-second rule: as the vehicle ahead passes a fixed reference point (a sign, a tree, a road marking), count 'one-thousand-one, one-thousand-two' — if you reach the same point before finishing 'two', you are following too closely. Two seconds is the minimum under good conditions. In rain, increase to four seconds. In heavy traffic, in poor visibility, behind a truck or other vision-blocker, increase further. The principle: at any speed, two seconds gives you enough reaction time to brake or maneuver if the vehicle ahead does something unexpected. Distance-based following measures (car lengths) are less useful because the safe distance changes with speed.