Harley Davidson Front End and Forks

Rake is the angle of the fork away from vertical toward the rider.  Trail is the distance on the ground between a vertical line dropped straight down from the center of the wheel and a projection of the fork extended until it touches the ground.  As the rake increases, the trail increases.  One of characteristics of Harley Davidson fronts ends is the more rake, the more stable the handling. Harley Davidson forks are designed to balance rake and trail.

There are many factors affecting the safe operation of a motorcycle.  Steering problems involve the design and geometry of the front end.  "Rake" and "Trail" are the terms associated with determining a bikes rideability.  The correct amount of trail for any given amount of front end rake is essential.  It determines the stability and control of any motorcycle.  For Harley Davidson Front Ends on chopper the the trend has been to extend the length thereby increasing the trail.

The rake is the angle of your steering neck compared to a line perpendicular to the frame.  Most choppers have a rake between 34 and 45 degrees.  The trail is the distance between a line drawn through the steering neck and a line drawn vertically through the front hub at the axle.  I have read various articles on the Internet that indicate trail should be between 2-4 inches and other sites that prescribe 4-6 inches of trail.

Bikes with a high amount of rake, like say 38 degrees and up, will give even a relatively light machine a heavier feel at the handlebars due to weight of the chassis trying to self-straighten the fork as it hangs in the steering neck.  A higher degree of rake, with proper trail will give better straight-line performance, but it will feel heavier and a bit sluggish during tighter turning.

Lower rake numbers, take for instance the 26 degree frames used on Harley's big touring bikes, make the heavier machines feel deceivingly lighter than they really are.  The big bikes are much more maneuverable than, say, a raked out softail, but these bikes do not track as well at very high speeds and that's why you'll find maximum recommended speed limits for them actually listed in the Harley owner's manual.

Another thing you may notice about some Harleys upon closer inspection, is that they use raked triple trees right from the factory.   In fact, the springer models have a specific rake angle for the 21-inch wheel, and one-degree less rake built into the trees for the Heritage Springers with the larger 16-inch wheel.  During their exhaustive testing procedures Harley found the fatter-tired bike needed to be de-raked one degree to stabilize the handling.

Either way you look at it, selecting your desired rake and trail is going to be a compromise in one direction or another.  You'll either have quick handling and a little less high-speed stability, or you'll have excellent directional control at salt flat speeds with a machine that feels a little heavier as turning radii decrease.

The problems with trail arise when the rake is set at extreme angles, such as 45 degrees or more.  This is a cool look, but it creates a very long trail (pic 2).  This is usually overcome by adding some offset in the triple trees.  The offset increases the rake, but greatly reduces trail.

Adding rake to the trees can be very dangerous as it reduces the trail and can quickly lead to a negative trail situation.

In cases where a frame might have too much trail due to excessive rake, the steering can be uncontrollably heavy and needs to be held at all times at low speeds to keep the front end from "flopping" over on it's own.  Although your bitchin' new frame might be the coolest thing you've ever seen, unless set up properly, it can be very dangerous to ride.  Cases like these can usually be cured very easily with the use of fixed-rake, or adjustable-rake triple trees.

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