Harold74

1) Thank you all for your gracious responses.

2) Many responders seem to have not picked up on the fact that I intend to NOT use my entire gear range when on the small ring. So the 33T capacity shouldn't rigidly apply as it normally would as I won't be using the full 38T demand. Rather, I'll be restricting my gear usage to suit the 33T capacity.

3) I plan to size my chain for big-big and, as such, I see the only difficulty as being small-small chain slack. So my derailleur math was basically small ring compared to as small a cog as the short cage DR would allow me to go at the back without the chain going slack (17 teeth). That calculation seems to be correct. Or, at the least, I've seen nothing here so far to indicated that it's incorrect.

4) The front derailleur will remain the Deore triple that came stock on the bike. So long as that's the case, and I'll not have chain slack, that should be fine, right? This is strictly rear derailleur fiddling.

5) I don't expect that anyone will ride this bike other than me. That was just a hypothetical and was me trying to solicit the "doomsday scenario" of what could possibly go wrong.

6) The Miyata was indeed intended to be a touring bike. That's not how I'm using it however. For me it's a cool, super comfy, fitness rider. There will be no touring. Like I said though, I want the granny ring option occasionally for the dog trailer. I have a separate bike that is currently the full time dog trailer hauler but I foresee a future in which I'm forced to divest myself of a bike or two and the Miyata is pressed into that role.

7) I don't want ANY long cage derailleur on the bike, no matter how cheap or how high a quality of a component it is. My reasons are unique to me and this project and are not altogether rational:

a) I'm in love with the frame of this bike and the comfort of the ride. I'm taking the bike in a non-vintage direction, modernizing everything that I can figure out how to upgrade for sport.

b) It may just be my imagination but I feel as though my short cage road setups shift more crisply than the long cage setup on the Miyata. And I LOVE crisp shifting.

c) As it stands, with the original long cage Deore derailleur, small-small is already almost unusable. The chain is loose and, on rough terrain, it bounces on (and scratches) a little bar on the chain stay meant to protect the chain stay in just such situations. Cross chaining isn't currently dangerous for me but, at the same time, it's hardly functional.

d) This more than anything else. I'm a structural engineer and, as a result, I view certain thing in certain, unorthodox ways. I see a long cage derailleur as a fragile, upside down cantilever. When I look down at it, it feels like it's the length of a baby's forearm and flopping around all ungainly like. I'm simply repulsed by it. And it's my bike so, if I say it goes, it goes.