Integrated Headsets Explained (continued)
March 2002
The Conventional
Headset:
At
right, you see the plain old, everyday headset. The little
picture underneath is a close-up of the cup and bearing
area. This is what it would look like if you split your
bike right down the middle. The bearing is press fit into
the cup (it won't come out and it doesn't move around
in the cup), then the cup is pressed into the frame. The
whole thing is trapped by the bearing cap and the crown
race on the fork. Only the inner part of the bearings
can move, the outer race is fixed to the frame. As you
ride your bike the forces being applied (hitting rocks
and bumps) are trying to shift the whole assembly around.
Other than when you are turning the bars to steer, there
are only 2 places where the assembly can shift (because
the cups and bearings are all securely pressed together
into the head tube):
1)Between the lower bearing and the base plate and
2) Between the upper bearing and the bearing cap.
These areas are called "dynamic surfaces", they
move all the time (see the appendix
page for the details).
Check out the Bearing Cap Picture
below. The aluminum bearing cap on the left is a new one,
the one on the right is a year old. This is perfectly
normal wear and tear. This wear is right at one of the
dynamic surfaces. Remember, we have headsets out there
that are 25 years old, we have learned a lot about headset
wear.
This wear is because the bearings and fork are always
moving. They move even when the headset bearings are firmly
attached to the head tube, like in a conventional headset.
The part of the fork that goes through the frame is called
the steerer tube. The steerer tube is always flexing around,
whenever you brake, turn, shift your weight or hit something,
the steerer tube is simply not staying straight. And the
bearings themselves have some play in them that can't
be adjusted out.
All of these factors together explain the movement
and corresponding wear on the Bearing Cap Picture.
Incidentally, a new bearing cap from us will cost you
a big $18 and you can replace it in 2 minutes flat using
one 5mm allen key.
