Originally Posted by
shelbyfv
And yet that's exactly what it is, no more. There are no "structural engineering concerns" with long cage derailleurs. It's fine to prefer one look over another, but you'd think an engineer would prefer a properly designed system over some kludge with a sagging chain.
Anyway, maybe a compact crank would give acceptable range while keeping the look you like.
I disagree. The cage is a column and a column's propensity to buckle varies with the square of its length. So a 50% longer cage is only about 45% as strong as the shorter cage. Originally I thought that longer cage derailleurs would come with laterally stiffer construction but, from what I can tell, that's not the case. Sure, long cage derailleurs don't fail this way and are, in that sense, well designed. That said, It would not surprise me at all to find that long cage derailleurs tend to age less well that short cage derailleurs for this very reason. The two vintage, long cage derailleurs that I own do seem quite "tired" relative to the vintage short cage derailleurs that I have. Maybe they always were softer, who knows.
Additionally, if you read my proposal in detail, you would know that there will be no sagging chain. I intend to specifically use my gearing in a way that precludes that.