I found the following on
http://calfeedesign.com/tech-papers/...bike-handling/
The paper is written about bicycles but the same theory applies to dirtbikes. Chilly was pretty accurate in his description of the Sherco ...
Fork Rake is also known as Offset, which more accurately describes what it is: the hub?s offset from the steering axis. Fork offset determines trail when considered with head angle (and the diameter of the wheel). Trail is best thought of as the tire patch ?trailing? behind the steering axis. More trail is nice at high speeds (motorcycles usually have 80 mm of trail) but can feel sluggish at slower speeds.
Head Tube Angle
Also known as the steering axis, this angle influences stability in combination with fork offset by controlling ?wheel flop?, or the tendancy for the wheel to turn when leaned.
A steep head angle is more upright and takes less effort to turn the front wheel, especially if there is too much rake or too little trail. A shallow head angle will want to turn too quickly when leaned if there is too little trail or not enough offset. So most shallow angle bikes have plenty of fork offset to compensate. Head tube angles range from 71.5 degrees to 74.5 degrees. The steeper head angle bikes are a little more agile, or require less effort to steer. People are usually very good at adapting to various head angle bikes if they have the proper trail.