We are often asked to manufacture raked triple trees. Our decisionNOT TO RAKE TRIPLE TREES revolvesaround the stability and handling of the bike, and the safety of you,the rider. Raked triple trees are scientificallyunsound, as explained below.
As trail is REDUCED, instability results, producing a naturaltendency towards deflection or speed wobble.
As trail is INCREASED, so does the ability of a motorcycle toresist wobble and follow a straight line. There is alimit, however – too much trail can result in a motorcycle only beingable to travel in a straight line!
TRAIL is geometrically determined by continuing a centerlinethrough the frame head to the ground, and drop-ping a vertical line from the center of the axle. The differencebetween the 2 points (corrected to the centerlineof the motorcycle) is measured in inches.
THREE DIFFERENT FORK CONFIGURATIONS SHOWING HOWTRAIL IS AFFECTED
A) Typical Stock Configuration
A 30° rake is established in theframe head. The fork is alsoat 30°, with no rake changeevident in the triple trees. Thetrail is lets say 3.5″
B) Raked Triple Tree
The Frame Head remainsunaltered at 30°. The triple treesare machined to produce 35° inthe fork. The trail vanishes tozero degree, producing grossinstability.
C) How it Should Be Done
>The components are the sameexcept that the Frame Head isreconfigured to 35°. The alteredgeometry increases the trail tolet’s say 4.25 inches and producesmore straight-line stability.
So what’s the solution? We recommend altering the frame head inorder to achieve the desired non-standardrake. Never consider the “easy way out” by choosing raked tripletrees. We would caution the rider to seek professional help inselecting a precision jig and only using sound, careful weldingprocedures.
Glossary
RAKE: The angle of the fork tubes, expressedin degrees off vertical. Also: CASTER
TRAIL: An imaginary distance arrived atgeometrically, expressed in inches.
FRAME HEAD: A tubular section of the framethat houses the assembled fork stem andbearings. It is a normally immovable part whichestablishes the rake of the fork.
TRIPLE TREE: Machined, forged or castplates which contain the fork tubes and fork assembly.Usually no rake angle is established here.
