Stay In, Drop Out

If you have been following this blog then you will be aware that I am very much a novice cyclist and have only come to this pastime, I would be ashamed to use the word " sport " in reference to my endeavours, since I retired.  One of the effects of this is that my ability to know instinctively when to change gear is poor. Whilst this  failing reduces my average pace in virtually all cycling situations, the most noticeable effect occurs when trying to change gear when the chainset is under severe load. This tends to occur when climbing and I suddenly need to change down gear as the gradient becomes too steep, or when I try to accelerate hard on a climb in order to attack the other riders.
I own two Mercians, one of them being a 1961 vintage Audax, which has a Horizontal Drop Out on the wheels

The power that I transfer to the pedals, and hence the chainset, under these conditions is such that the rear wheel twists in its supports causing the tyre to rub against a chain stay. I once road 35km in the Derbyshire Peak District under these conditions and struggled to keep up with the rest of the peleton to such an extent that I considered abandoning the ride. It was only when a more experienced cyclist pointed out that I had been doing  severe resistance training up the peaks and corrected the problem was I able to continue.

My new Mercian Vincitore Special ( 2012 ) has a different design for holding the rear wheel in place.

This is engineered with Vertical Drop Outs and I suspect is a much improved design feature as there is nowhere for the axle to slide. In any event, I have yet to experience any inadvertent resistance training.
But it could be that the chrome plated stays on the vintage Mercian are the problem and that horizontal drop outs do have advantages over the vertical type.