As I said, I have zero doodle bug experience, nor do I build mini bikes that are so fast this is an issue. :laugh: As far as what could be done to mitigate the zero trail, I listed the options above. Take your pick depending on how much fabrication vs. what look or stance you want, vs. how much trail you want. :shrug:
It isn't just lack of offset on the trees, it is a combination of that, axle placement with relationship to the plane of the neck, axle height from the ground and anything else that moves the center of effort on the front axle, to an undesirable zero or aft of the plane of the neck.
You can read about this on line, but most of the solutions are tailored to the motorcycle world. I started researching it many years ago, after purchasing a book, all hand drawn illustrations and solutions on how to build your own chopper, or something like that. I may still have the book buried somewhere.
The first thing to do is measure your rake and trail. With my limited tools, I'd be more inclined to knock the neck out another degree. Once you jig up the bike, you can play around with string and a protractor to get some idea of where you want to be, and what rake angle it would take to be there.
Use a piece of tape under the front axle, with zero starting exactly centered on the axle, perpendicular, down to the tape. Then measure forward and mark off the inches. Then run string from down the neck to the tape and mark it. It should come out about 2 inches in front of that zero mark for your run of the mill mini bike from my personal testing of smaller frame bikes.
Here is a link to a few years ago, surprisingly similar to this conversation.
Edit: All measurements are taken on the ground. Not at the trees, or anywhere else. You are looking at two plane relationships, neck angle down to the ground, not the down tubes. Then exactly vertical from center of axle down to the ground. Measure the difference. That is trail.
