Originally Posted by
Road Fan
The correct measurement will be small - 35 mm for low trail to 60 mm to emulate the vast majority of erstwhile racing bikes. It's easy to get it wrong.
I assume the OP bike is vintage? East German? If so i would not imagine Trek have any real data. Id assume the geo is 1960s, so id guess that 50 mm rake (not trail!) is a reasonable build target.
On a flat, level floor, with round wheels, the contact point has to be directly below the hub/axle. Think about it. No need to even have the bike attached.
Dancingbear linked to the Wikipedia article about
Bicycle Geometry
Trail and Rake are measured with respect to an imaginary line drawn down from the center of head tube.