Originally Posted by
Doug Fattic
Yes, frames built curing the classic era with limited and somewhat primitive tooling required horizontal dropouts with screw adjusters (or some kind of adjustment) to get the rear wheel to center. Any error in chain stay length gets magnified at the tire end of the wheel at almost a 3 to 1 ratio. Even today's modern and expensive fixtures don't guarantee a center wheel result.
i agree that a "horizontal" dropout allows a bit of error that won't be seen, but one of the definite origins would go to the first Campagnolo shifting mech, the Cambio Corsa and its children. There the teethed dropouts HAD to match left and right, Campagnolo even made a tool to assist.
about 1952-53 the Gran Sport mech was accepted enough to supersede but the. Basic design, now without teeth and with a forged derailleur tab, initially with 4mm adjusters, soon revised to 3 mm set the stage as THE defacto Italian dropout of choice.
then the advantage of integral no tool required adjusters was the standard.
it was so accepted that it became the signifiers of a quality frame, not always the case but helped. Marketing! Lygie, Atala, Italvega, Legnano all exploited it. The fork was short changed, but the rear dropouts were tops.
If Campagnolo had not taken a half hearted view of the "vertical" dropouts things may have moved faster. But builder alignment would still need to be better than with horizontals.