IS THE ENDO
Going over the handlebars can happen in an instant, or, even worse, it can take three seconds. The worst endos take
place in slow motion when the rider teeters on
the front wheel like an inverted unicycle rider.
Time expands as you coast down the track on
your 230-pound teeter-totter, staring at your front
fender, holding your breath in silent anticipation
of the yard sale that you will soon be hosting on
the front straightaway.
By Richard J. Cunningham
What is an endo? An endo is a forward roll
where the rear of the bike comes up and over the
front wheel. The opposite of an endo is a loop-out.
Sooner or later, every racer will endo. It is inevitable. And when your number comes up, you will
be deposited on the earth by your trusty steed
like all those who have preceded you.
In this chapter of MXA’s extension course in
moto physics, we will tell you how and why motocrossers go over the bars.
CENTER OF GRAVITY
“Center of gravity” is defined in
Funk and Wagnalls as “the point
in which a body near the earth’s
surface, acted upon by gravity or
other parallel forces, is balanced in all
positions.” Your motorcycle, along
with everything tangible on this
planet, has a center of gravity. In engineering terms, it’s simply called the
“CG,” but most of us call it the “
balance point.” Motocross chassis designers go to great lengths to place the
engine, wheels and suspension components in exactly the right location
to get a motocross bike’s CG perfect.
The higher the CG is located on a
motorcycle, the more likely a bike is
to endo. Paradoxically, you will be
horrified to discover that the CG of a
modern motocross bike is purposefully
high—way high. For a machine that is
required to skim across the earth, fly
through the air and swivel about its
CG, a high center of gravity is a plus.
One of the tools of any motorcycle
racer is weight transfer. It makes a
228-pound machine feel light or heavy
depending on what the situation calls
for. When a motorcycle accelerates
forward, the bike rotates around its
CG, causing the front tire to get light
and weighting the rear tire. Because
of this weight transfer, there is a heap
of traction on the back tire when a
racer needs it most—roosting out of
a corner. The downside of this is that
when a bike decelerates, the motorcycle’s mass rotates towards the front
wheel, and it is possible for the rear
wheel to lift. This dance of fore-and-aft
weight transfer is the root of all endos.
Knowing exactly how to endo on
purpose might be the best way to
avoid repeating the incident by accident. It isn’t as easy to loft your rear
wheel as it is the front (as anyone who
has practiced nose wheelies can attest
to). The good news is that on level
ground, a motorcycle won’t flip end
over end on its own. You have to help
it. To accomplish a controlled endo,
you’ll need to transfer your weight
and the mass of the motorcycle up
and forward. This requires an unnatural act on the rider’s part (leaning over
the bars and grabbing a fistful of front
brake) or a natural feature (such as a
bump or a deep rut).
Here are the actions that allow a
bike to endo.
(1) The weight shift: Smacking a
sharp-faced bump at speed will cause