should be measured from. For example, a CRF450’s head
angle is listed as 26. 52 degrees, because Honda measures
it from the front of the fork. But, in the bicycle world, this
would be called a 63.48-degree head angle (as measured
from the back side of the fork).
The confusion comes when people don’t understand that
the head angle is derived from a 90-degree base number.
A 26.52-degree head angle is the same as a 63.48-degree
head angle ( 90 – 26. 52 = 63. 48). It is simply two ways of
describing the same angle.
WHAT ARE TYPICAL HEAD ANGLES? Motocross
bikes have head angles in the range of 27. 5 to 26.0 ( 62. 5
to 64 degrees). A 27.5-degree head angle is not as steep
as a 26-degree head angle. Steeper head angles turn more
instantly and in a smaller arc. The slacker the head angle,
the more the front wheel will resist turning, the larger
the turning arc will be, and the easier it will be to hold a
Motocross bikes of the ’70s typically had 30-degree
(60-degree) head angles. They were called “slack” head
angles. Slack is the converse of steep.
HOW IS TRAIL MEASURED IN MOTOCROSS? It’s
a simple measurement. Extend an imaginary line down
the center of the steering axis to the ground. Then, drop
a perpendicular line through the center of the front axle
to the ground. The distance between where the two lines
intersect the ground is the trail measurement. As a rule of
thumb, it should be between 3 and 5 inches.
WHAT EFFECT DOES TRAIL HAVE ON A BIKE?
A longer trail measurement means greater caster effect,
heavier and slower steering and a more stable feel in a
straight line. Reducing trail causes the bike to steer lighter
and quicker and the front end to feel more nervous in a
All geometry measurements are taken from a bike that is
standing on level ground. At the factory, trail is calculated
on an engineering program, taking into consideration what
the engineers feel will be the correct static sag setting.
Some chassis engineers also refer to trail as “wheel caster.”
WHAT IS FORK OFFSET AND WHY DO PEOPLE
CHANGE IT? Fork offset is the measurement of how far
the fork legs sit ahead of the steering axis. To obtain the
correct number, measure the distance from the center of
the fork leg rearward to the center of the steering stem.
Offset is used primarily to determine the correct amount
of trail for a given head angle. Motocross front ends
typically use between 18mm and 25mm of offset.
More fork offset reduces trail for a quicker steering feel
and less stability. Trail is increased with less fork offset.
Fork offset is a term that is used more by aftermarket
triple-clamp-makers because they offer clamps with various
offsets that are used to create handling characteristics that
are different from stock.
WHAT’S THE HIDDEN SECRET OF FORK
OFFSET? A little-considered fact is the role fork offset
plays in the steering process apart from establishing
trail. The weight of the wheel and most of the fork is
offset above the steering axis, while the wheel contacts
the ground behind the steering axis. This creates an
interesting relationship. As you lean the bike into a turn,
the weight of the bike leaning off to the side automatically
forces the wheel to turn into the lean. The more the wheel
is offset, the more the fork will steer into a turn when the
bike is leaned.
IS IT BETTER TO ADJUST OFFSET AT THE
FORK OR AT THE AXLE? Fork offset can be changed at
the triple clamp (by moving the fork legs closer or farther
away from the steering stem) or at the axle lug (by casting
the lugs so that the front axle is a specific distance away
from the center of the fork legs). In 2004 Honda wanted to
change the offset on its bikes, but rather than change the
triple clamps, Honda had Showa pull the front axle back
2mm to give the CRFs more trail.
IS IT BETTER TO CHANGE OFFSET AT THE
CLAMPS OR AT THE AXLE LUG? As a rule, changing
trail at the axle is better than at the clamps. Why? The
more offset at the triple clamps, the more the rider will
feel the weight of the fork tubes when steering. Although
there needs to be some offset at the clamps to give fork