EXAC TL Y WHERE IS THE CEN TER OF GRAVI TY?
The center of gravity is, roughly, the point where the
combined mass of the rider and motorcycle are balanced
in all directions. Saddle height, the position of the engine
within the frame, and ground clearance establish the
center of gravity (CG) when the rider is on the bike.
Ground clearance: The amount of ground clearance is
largely determined by the amount of suspension travel. To
prevent your feet from being swept off the footpegs when
the suspension bottoms out, ground clearance will always
be an inch or two more than the suspension travel.
Seat height: Motorcycle engineers choose a seat
height that positions a rider of average height
and weight at a balance point near the center
of gravity where small body movements will
have a strong effect on braking, steering and
acceleration. If the CG is too low, the rider
won’t be able to transfer weight properly
over the front or rear of the bike. If the
center of gravity is too high, too much
weight will transfer from front to back
during accelerating and braking, causing
the bike to bounce all over the place
through the bumps.
Engine position: Computer programs are
now responsible for engine position. They must
factor in not only the weight of the engine, but
the gyroscopic effects of its internal motion.
Once the computer selects the optimum
position, factory test riders confirm it during
Changing suspension sag, handlebar height, footpeg
location and the thickness of the seat are options for a rider
looking at raising or lowering a bike’s center of gravity.
WHAT IS WEIGHT BIAS? “Weight bias” is how the
percentage of total vehicle mass is divvied up between
the front and rear wheels. It’s kept as close to 50/50 as
possible—with and without the rider on board. With shared
bias, it takes less input from the rider to make the front
stick in corners or the rear tire hook up out of corners.
The rider controls the front/rear weight bias by moving
forward or back over the seat.
HOW DOES GROUND CLEARANCE RELATE TO
THE OTHER NUMBERS? Motocross geometry must be
built around ground clearance. If you have 12 inches of
suspension travel, you need at least 13 inches of ground
clearance and a bit more peg height. Bikes with
less travel and lower ground clearances will have
a lower center of gravity. A lower center of gravity shifts less weight
from front to rear when
accelerating and braking, and, because of
this, the bike can
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