Triple Tree ("triple clamp" (US) or "yoke" (UK)) attaches the fork tubes to
the frame via steering head bearings, which allow the forks to pivot from side
to side, and therefore steer the motorcycle. Most bikes have upper and lower
triple trees, providing two solid clamping points that keep the fork tubes
parallel whilst also connecting the forks to the frame via the steering head
bearings.
With
the tendency to employ fork legs with single action damping, fork triple trees
need to be reinforced more than when the forks shared both damping roles,
because the rigidity of the triple trees is relied upon to distribute the forces
within the forks without flex.
The
triple tree is closely related to
rake and trail and by changing the triple tree
you can actually adjust the rake and trail.
Triple trees have a dimension called off-set. It is the
distance from the center of the fork tubes to the center of the neck pivot axis.
It is an important factor in trail. The better manufacturers of raked triple
trees reduce the off-set in order to increase trail in the final set-up.
With a rake of 5 degrees added to the frame and 5 degrees
added to the triple tree and a reduction of off-set in the triple tree we have a
bike with a longer wheel-base, a prettier front-end and a trail dimension close
to the original.