Getting the chain stays to be the exact same length (so a rear wheel is exactly in plane with the centerline of the front triangle) is one of the greatest if not the greatest challenge in building a custom frame. I encourage my framebuilding class students to choose horizontal dropouts for this very reason. In the old days before precisely machined frame fixturing, the adjustable screws could compensate for any discrepancies. Seat stay length is not quite as difficult because the chainstays are already brazed on providing some rigidity for checking the seat stay length. A difference of a millimeter in stay length is exaggerated by the physics of a wheel. In other words a mm of difference in a stay length will result in something like 3 mm of the wheel rim being out of plane.
I know from experience of reconditioning classic frames that most of them will not center a rear wheel perfectly. Most likely they are off at either or both of the chain stays or seat stays. Stick a perfectly trued and dished wheel into your frame and find out for yourself.
Doug Fattic, Niles, Michigan USA
From: John Betmanis wrote:<johnb@oxford.net>
A couple of reasons I can think of:
1. It's a carry-over from the way road bikes were always made, before derailleur gears were common. Tradition.
2. "Vertical" dropouts require very precise frame building with no means to alignin the wheel if the frame comes out a little "off".
At 08:01 AM 26/08/2009 -0400, Stronglight49@aol.com wrote:
>Stupid questions:
>
>1.) Noticed something in the photos of the Della Santa frameset
>which brought to mind something which I never understood.
>Is there a reason for using horizontal dropouts on a modern
>road bike frame built for use of a rear derailleur?
>
>Call me lazy, but I really hate fidgeting with the rear wheels on
>my old bikes - especially those (now most) which have mudguards
>fitted.
>
>I have my own theories about the need for long dropouts -
>something which was never required (or wanted) on classic
>Touring bikes, even during the 1940s.
>
>So, next question:
>
>2.) What was the TRUE reason for use of long (or even shorter)
>horizontal dropouts throughout the On Topic period?
>
>Feeling rather naive, but it seems that design of most ANY derailleurs
>produced during the past 25 years or more have finally made horizontal
>dropouts... as obsolete as buttons on trouser flys.
>
>BOB HANSON, ALBUQUERQUE, NEW MEXICO, USA