The Cessna 120-140 Association Forum

This illustration is from the very comprehensive Neil Wright article on the tailwheel assembly and alignment. While I understand the vertical reference line, it's not clear what the tilted line is referenced against. Any help appreciated.

Try looking at it like this instead....

The top of the forks has a level plane that needs to be tilted backwards a little. This is my bird, this pic shows the slight tilt rear-ward. You want it to have a slight tilt rear-ward or pretty much level. Otherwise you get the 'shopping cart' wobble.
Here's a pic hopefully showing what we're trying to describe...

And here's an extreme view of the 'rear-ward' tilt, when I had the incorrect double-bend mainsprings on my bird. The tail was so much higher, I couldn't make a decent 3-point landing so I became a 'wheelie' guy.

Thanks for the quick reply - very helpful.