What is it?
Rake is (or at least should be) always defined as the shortest distance between the pivot axis and the axle axis of a hanger. In the rightmost representations above, it can be seen as the distance between the centers of the green circles and the extended axis lines. Included were some angled representations of both extended axis lines from different points of view (leftmost pictures). As this is a RAW Precision hanger, its rake is 2mm.
What isn't it?
Rake often is, but never should be defined as an angle simply because the "measurement" of such an angle is relative/suggestive and doesn't pertain to any solid geometry in a hanger. When I see a company's rake stat presented as an angle, I can only assume they measured from the end of the pivot. Which really has no significance to the turn/lean aspects of a truck because no matter how long or short a pivot is, a truck will still hold the same pivot axis, and therefore the same geometry, but if they change the length of their pivot, this "rake angle" will change along with it. Many such companies have even admitted that this way of representing rake is incorrect, but then claim it helps potential customers understand how rake affects how a truck will feel. This is done by subtracting the rake angle from the baseplate angle if rake is negative (axle closer to board), or adding the rake angle to baseplate angle if rake is positive (axle closer to road). That part makes me the most frustrated, because there is no way flipping a hanger will affect how a baseplate reacts to lean, especially with RKP trucks, as the bushing seat plane is (or at least should be) always aligned with the pivot axis.
So, I've disproved this rake-measurement-by-angle method with reasoning, next I'll disprove it by analysis of data I collected.
So, I've disproved this rake-measurement-by-angle method with reasoning, next I'll disprove it by analysis of data I collected.
Hard Data
Angle: The controlled angle between the ground plane and the board/baseplate face plane, in degrees. This was the independent variable.
Y: The vertical distance between the end of the blue line where it intersects with the dashed line (span from the centers of each axle) in the pictures above, and the center of gravity of the setup (yellow ball with axes and planes sticking out of it), in millimeters.
Delta Y: The difference between the Y value at 0 degrees and the Y value at the current angle, in millimeters.
X: The horizontal distance between the end of the blue line where it intersects with the dashed line and the center of gravity of the setup, in millimeters.
Turn Radius: Measured radius of the blue arc in the pictures, in millimeters.
Inverse of Turn Radius: This was calculated by dividing 1 by the turn radius. I did this to better quantify "turniness", where with the normal measured turn radius, a higher value means it turns less quickly, now with the inverse, a higher value indicates more/faster turning.
Y: The vertical distance between the end of the blue line where it intersects with the dashed line (span from the centers of each axle) in the pictures above, and the center of gravity of the setup (yellow ball with axes and planes sticking out of it), in millimeters.
Delta Y: The difference between the Y value at 0 degrees and the Y value at the current angle, in millimeters.
X: The horizontal distance between the end of the blue line where it intersects with the dashed line and the center of gravity of the setup, in millimeters.
Turn Radius: Measured radius of the blue arc in the pictures, in millimeters.
Inverse of Turn Radius: This was calculated by dividing 1 by the turn radius. I did this to better quantify "turniness", where with the normal measured turn radius, a higher value means it turns less quickly, now with the inverse, a higher value indicates more/faster turning.
When setting out to try and uncover how rake really works, my first thought was to see how it affects the characteristics of a setup as a whole, because that's actually what is felt when riding, whereas most look only at the truck itself to try and figure rake out. So I thought "what's the most apparent characteristic of a board that is felt when riding?" and discerned it to be a setup's center of gravity (center of mass). Whether this is correct or not, I'm not certain, but I gave it a shot because Autodesk Inventor finds the center of gravity of 3D parts accurately and automatically. As you can tell from the graph, the two lines follow the same relative path, with a small discrepancy between them. This difference is most likely explained by the change in ride height when I flipped the hangers in my model, and not as a characteristic of the rake itself. So my hypothesis was rendered inconclusive.
I made this graph to further disprove the widely accepted notion that rake alters baseplate angle. You can see that the two trend lines are essentially right on top of one another, meaning rake has no effect on the lean-to-turn ratio of a truck. The small difference between the two lines can be accounted for by a small change in truckbase (distance from axle center to axle center) of about 3mm occurring when the hangers were flipped. This graph also completely disproves Sabre's ridiculous chart of the lean-to-turn ratio of a rakeless hanger compared to a raked hanger.
In conclusion
My hypothesis about the center of gravity offset being affected by rake turned out to be wrong, but I have a few more complex ideas that may turn out to be correct. I'll be bringing this issue up with my Statics professor soon, because I have a feeling there is something about rake acting as a moment arm which affects how it feels. So that'll be Part 2 of this delving into how rake works.
If you have a thought-out, lengthy, and relatively scientific idea of how rake works, please don't post it in the comments. Instead, email me ([email protected]) and I'll see if it makes sense to me.
If you have a thought-out, lengthy, and relatively scientific idea of how rake works, please don't post it in the comments. Instead, email me ([email protected]) and I'll see if it makes sense to me.