The problem with down tube length is that it depends on fork-crown-height.
If you had two bikes, one with a small wheel and short travel fork, and long headtube, and one with a big wheel and fork and short headtube, they might have identical fit and angles, yet the downtube would be very different.
May 28, 2019, 7:09 a.m. - Tjaard Breeuwer
The problem with down tube length is that it depends on fork-crown-height. If you had two bikes, one with a small wheel and short travel fork, and long headtube, and one with a big wheel and fork and short headtube, they might have identical fit and angles, yet the downtube would be very different.