When you grab your front brake or hit a bump, the frame
wants to continue moving forward (blue arrow), while
the wheel wants to slow down (red arrow). As a result
of this, the fork flexes backwards. Headsets can't make
the flexing go away, that's in the fork design. All
forks flex, you've all seen it when you hit your front
brake and watch the front wheel. Most of the flexing
appears to be in the fork legs, but the steerer tube
(the part of your fork that is inside the bike frame)
is also flexing. All of the forces that slow the bike
down and bend the fork must act through the headset
bearings.
The pictures in this appendix show the
position of the lower headset bearing in these 2 riding
conditions. The first set of pictures show the bearing
positions when there are no forces pushing on them. The
second
appendix page shows the bearing positions when the
front brake is applied. Notice the gaps that open up as
the fork and base plate move when you grab the brakes.
This picture shows the conventional headset at rest,
no forces are acting on it. The bearing is fixed in
the cup, the cup is fixed in the frame. The only place
where the assembly can shift is between the base plate
and the bearing. This area is called a "dynamic
surface" and is indicated by the 2 red arrows.
The arrows show how the base plate can scuff back and
forth against the bearing. This same action happens
at the other headset bearing (the one next to your stem).
That's why we say that there 2 dynamic surfaces in a
conventional headset system. One on the top bearing,
one on the bottom (only the bottom one is shown in this
image).
This picture shows the "Integrated" headset
at rest, no forces are acting on it. The bearing is
resting against the frame, held in place only by the
headset adjustment. If you remove the fork, the bearing
falls out. Compare this picture with the one of the
conventional headset. Notice how this picture has more
dynamic surfaces (the 4 red arrows). These are a extra
places for the "integrated" headset assembly
to shift around. These arrows show how the parts scuff
back and forth against each other. That's right, the
bearing scuffs against the frame. This same action happens
at the other headset bearing (the one next to your stem).
That's why we say that there are 4 dynamic surfaces
in an integrated headset system. Two on the top, two
on the bottom (only the bottom two are shown in this
image).
