clearance for turning radius, the less offset the better to
decrease the fork’s moment of inertia. The lightest-steering
bikes will put as much of the given offset as possible into
the axle clamps.
CAN YOU CHANGE TRAIL BY RAKING THE
FORKS? Yes, but it is rare. Some works triple clamps are
designed to angle the fork tubes differently from the head
angle. Obviously, raking the forks away from the head
angle would increase trail and vice versa, but this is not
the way most manufacturers adjust for trail or offset. And,
it should be noted that changing the angle of the fork in
the triple clamps (by raking them) does not change the
head angle of the bike in any way.
The biggest effect of raking the forks, apart from a
change in trail, wheelbase and weight bias, is the effect on
suspension action. Slacker fork tube angles make the fork
less responsive to chatter bumps, flat landings and slap-downs but more yielding to square-edge and large whoop
impacts. Steeper fork tube head angles cause the fork to
compress more when braking into corners and react better
to flat landings.
WHAT FRAME NUMBERS MAKE A BIKE TURN?
The perfect steering geometry is the correct relationship
between the bike’s head angle, weight bias, overall wheelbase, front center (distance from the axle to the crank
center), fork offset and trail. Thus, changing one number
will affect all the others.
It’s no secret that how the bike is set up can alter the
steering geometry. Something as simple as more race sag
in the rear shock, different tire profiles and even lower
tire pressure can be used to fine-tune the way the front
end handles. Any adjustment that drops the rear of the
bike will slacken the head angle, slow down the steering
and increase the trail measurement. Likewise, trail will be
reduced and the steering will feel quicker if you run more
shock preload or a larger-diameter rear tire.
HOW IMPORTANT IS WHEELBASE? Wheelbase
is the distance between the front and rear axles. A
longer wheelbase turns slower, tracks smoother over rough
terrain and is less affected by rider position. Shorter wheelbases are more responsive to weight shifts, turn quickly
and ride roughly. Motocross wheelbases typically fall into
the 58-inch range.