Your front suspension geometry is defined by the following
six variables which are defined as:
OFFSET: Centerline of the top steering neck to the
centerline of the top of the fork tubes.
RAKE: The angle in degrees of the steering neck from
the vertical cord.
FORK LENGTH: The distance between the top of the fork
tubes to the centerline of the axle.
DIAMETER: The diameter of the front tire.
TRAIL: The distance defined by the vertical line from
axle to ground and the intersection of centerline of
the steering neck and ground.
RAKED TRIPLE TREES: In order to bring trail figures
back into line, triple trees with raked steering stems
can be used. Usually adjustable in 3, 5, 7 degrees of
rake.
HOW TO MEASURE CORRECT TRAIL
Raise the bike to an upright position, using a tape
measure, hold the tape straight down from the front
axle to the floor. Put a mark on the floor at that point.
Then place the tape parallel to the steering neck, following
the angle of the steering neck all the way up to the
floor. Put a mark here also. Now measure the distance
between the two marks and you have your trail measurement.
It should read between 2 and 4 inches. Note: If your
bike is equipped with a rear suspension, have someone
sit on the seat when you make the measurements to simulate
your actual riding condition.
TOO LITTLE OR NEGATIVE TRAIL
With too little or negative trail (steering axle mark
behind the front axle mark), the bike will handle with
unbelievable ease at low speeds, but will be completely
out of balance at high speed. It will easily develop
a fatal high-speed wobble. EXTREMELY DANGEROUS!
NORMAL TRAIL
Normal trail is somewhere between 2 and 4 inches. The
bike will handle easily at both high and low speeds.
Flowing smoothly through curves without swaying or wobbling.
If you use a very fat rear tire, you should keep the
trail as close to 4 inches as possible.
TOO MUCH TRAIL
If the trail is more than 4 inches the bike will handle
sluggishly at high speeds. It will seem almost too steady.
You will have trouble balancing the bike at lower speeds
or on winding roads. It will feel generally sluggish
and clumsy.
RAKE
& TRAIL CALCULATOR
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