Here’s a diagram to make sure you’re following the terminology.
Pivot axis is defined by the location of the two pivot centers, center of the bushing seat, and the center of the far joint. You probably already have a good grasp on that.
But for the axle offset, I’m meaning just the distance of the axle to the orange line of the pivot axis. So anywhere along that orange line would be zero offset, even though the axle is not directly over the pivot center in the bushings ( like it is in Stooge’s NKPs )
In terms of negative/positive rake, if the axle is on the board side of the pivot axis that’s negative rake, and if its on the roadside its positive rake.
Something like this will probably feel better.
Positive and negative rake does have to do with trail, but trail itself is an effect that happens on the ground plane. Where the pivot axis projects onto the ground and whether the contact patch of the wheel is in front or behind it.
Here’s my video where I talk a little about that.
You’re totally right in that by making the truck the way you are adding trail, which is the same thing as caster. The problem though is that trucks are mirrored front to back, so unless your front/rear trucks are different, while you may have have more stable positive trail on the front, you end up with unstable negative trail in the rear. And that having negative trail on the rear is pretty bad news.
Going back to the diagram. You can change your rake from negative to positive, and still keep that cantilevering suspension action. That cantilever action is also something that parallels design in kingpin trucks. Though, it is slightly different.
A TKP truck has an axle that is offset with lots of positive rake, but with the axle sitting between the pivot centers.
Which would be like this:
More or less.
By moving your axle between the pivot centers you’re allowing more of the load to be taken off of the bushings and more of it to be taken up by the fixed pivot. Makes for a harsher ride the more weight you put on the fixed pivot, but the less pre-load the board side bushing receives which lets it perform better.
RKP trucks have the axle sitting beyond the pivot center, forming a cantilever like in your design. This is done because it easily provides a good geometry with low rake, but the added bushing pre-load can actually be problematic. This one of the issue which queenpin truck are largely designed to combat.
Like the Ronin Truck which uses a preloaded support pin.
I’m not going to say the cantilever is bad, because obviously RKPs all do it as well. But you do want to be aware that one of the big consequences is additional bushing preload, and hampered response from your boardside bushing. At the very least your boardside bushing will probably want to be made a lot harder than your roadside bushing, quite a bit more than ususal.
