Originally Posted by
maddog34
is the top tube slanted to the rear any amount?
if so, Ignore the Seat tube spec completely.
i measure a phantom "top tube" in a horizontal plane... center of seat post to center of head tube.
....
The term I see often is “Effective Top Tube”. Or “Horizontal Top Tube”. Mostly referring back to the olden dayes when a top tube was parallel to the ground,