Originally Posted by Andrew R Stewart

I always like to start a headset adjustment with a tad of slop/rock. It can be hard to tell if a bit over tightened preload is present as there's so much leverage that the bars and front wheel can offer the bearings one can still turn the fork (to steer) even when the adjustment is too tight. Starting with a tad of rock and trial and erroring to no slop but still free fork rotation is the best way and what I train those who work for me to do. By turning the fork (and wheels/bars as a headset adjustment is only valid after all is assembled) 90* and repeating the front brake on and rocking fore and aft can offer more data. Especially with suspension forks or disk brakes as both can induce some slop most noticeable when the wheel is pointing straight ahead. If the headset is a tad loose the bike will rock the same amount regardless of how the fork is turned. Now if the headtube/crown seat isn't faced properly, if too many balls are installed, if the steerer is bent or if the headset is VERY BADLY and unevenly worn the amount of rock/slop will vary with the fork's rotational position. Andy