IT’S ALL ABOUT GRAVITY
In a sense, motocross bikes make their own gravity,
because you must lean them to turn. When a motorcycle is
leaned over at speed, the G-forces are directed down the
wheels. So whether a motorcycle is rolling in a straight line
or banked at 80 degrees around a berm, it is pinned to the
ground by whatever G-force it can muster.
To help you understand the concept of G-forces, think
of a turning motorcycle as a ball spinning on the end of
a string. Now, imagine a vertical line from the top of the
rider’s helmet down through the center of the bike to the
ground. The rider balances his lean angle and the speed
of his motorcycle with the radius of the turn to create a
G-force along this centerline. As long as the racer carves an
elliptical arc, he can stay pinned to the surface, as we have
all seen at the circus when performers ride at 90-degree
angles on the Wall of Death; however, if anything causes
the G-forces to move right or left of the center line, the
motorcycle will either fall into the corner or try to high-side out of it.
Agreat motocross racer once said that when he puts one foot out, he is signaling that he is slightly out of control, but both feet out means that he is absolutely out of control. He makes a good
point. Every racer hangs a leg out, but it never happens when his confidence
is at its peak. Who hasn’t flailed his way out of a monster rut with the throttle pinned and both legs trailing behind like course markers in the wind?
Who doesn’t instinctively extend a leg when he enters a treacherous corner?
The question at hand in this edition of “Moto Physics 101” is whether or
not a motocross bike needs outriggers.
A savvy rider can fix a wavering G-force line with
minimal steering or throttle input. If you are railing a berm
and your motorcycle starts to fall over to the inside of the
turn, you can change the steering input or give the bike a
handful of gas. If you are high-siding, you can
steer towards the direction of the crash or
chop the throttle.
G-force is our friend when we keep it
on the center line, and our enemy
when it gets out of whack.