Slackening the head tube angle increases trail (the distance the tire's contact patch trails behind the steering axis). Lengthening this distance increases stability; it becomes more difficult to deflect the wheel.
Alternately, steepening the head angle shortens trail, leading to quicker handling. Too short and the steering becomes what is often described as quirky / twitchy.
Alternately, steepening the head angle shortens trail, leading to quicker handling. Too short and the steering becomes what is often described as quirky / twitchy.
