CliffordK

The answer is that the horizontal dropouts have worked for over a century, either forward facing, or rearward facing.

Initially incorporated on the bikes for 1 and 3 speed hubs, there have been a number of changes including quick releases, and different skewer types. And, of course, the Cambio Corsa and derailleurs.

Most people using horizontal dropouts have had a wheel slip, usually not causing the wheel to lock, and almost never falling out, but causing rubbing.

Of course, many single speed bikes have also incorporated a tensioner/keeper to keep this from happening, but that hasn't been widely adopted by multi-speed users.

So, for the most part, it is not a hazard. And, probably not a design flaw.

However, there are a few things that make vertical dropouts better for many applications.

• Less slipping.
• Tire doesn't bump into seat tube when mounting/removing.
• Quicker/easier wheel removal.
• 

Some companies are still adding horizontal dropouts to their bikes in one form or another. Some are convertible between single speed and multi-speed.

One argument is that cutting a chain to single speed can be a last ditch self-rescue option in case of drivetrain failure.

As noted, many of the new skewers incorporate a plastic bushing that gives just enough flex that they're problematic with the horizontal dropouts. So, be careful with jumping between technologies.

Bill in VA

It happens, usually not to that degree of jamming the frame, but I remember some skewed riding from a tilted wheel.. My current bike has verticle drops, but that was not a decision point for me, even though it makes removal quicker and less messy with chain lube.

I rode a chrome dropout frame for years. If it ever moved, it was because of my not clamping it tight "enough".. The Campy skewers you have are far superior to open levers. Even my skewers that did not have actual teeth or grooves would not move if tightened and I have been a heavier rider and did out of saddle riding.

My call: not a design flaw. Given the 32 years of it not happening, it is probably an operator error and as such is highly unlikely to happen again.

Cyclist0108

It was probably a combination of bad luck, my desire to cram as wide a tire in there (28mm) as possible, not having the skewer tight enough, and having the frame cold-set (so it is ever so slightly sprung now relative to the hub).

At least within the confines of my caliper, the drop-outs are parallel, and they are thick enough to accommodate the White Industries hub.

edscott.

Maybe vertical drop outs have less risk, but in the end are worse. A few weeks ago a friend went down when he rode over a pothole and the rear wheel came off, He got bruised and scratched up pretty bad. His bike has vertical dropouts.

This has convinced me that vertical dropout are in fact a step backwards in design, since the wheel will come off in more dangerous circumstances. I've had the rear wheel with horizontal dropouts come loose when applying torque, but it never comes off, since it just come to a halt against the seat tube. And it always has been because of loose or inadequate quick release..

Another plus of horizontal dropouts is the tiny screw which lets you move the wheel axel back or forth to accomodate to the derailleur geometry and fine tune indexed shifting if that pleases you..

Front wheel dropouts is another matter. Now they have tiny stops that avoid the wheel coming off, but you only appreciate this after you have had the wheel come off. But by then you learn to always lock the quick release facing up. That way gravity will make it face downwards if they become loose.