The only difference is basically that the three main tubes are double butted cro moly on the LTD. versus straight gauge for the S12S with the fork and stays on both being hi tensile. I can say that the standard S12S is a very nice ride, predictable and quite stable. I am using Grand Bois 42mm tires so they do fit with fenders which is not something very common among road bikes of this vintage. They are basically sport touring with 44 cm chain stays and yet the bike handles surprisingly well and while not a racing bike I find it agile and easy to steer. If you get the fit right it just disappears and you simply get out and ride, enjoying the scenery. Even when loaded with a few pounds in the front bag it does not feel heavy when moving along, the steering will get less responsive with enough weight but the bike remains stable. I have had over 10 pounds and it was not bad at all.
It is true as gugie suggested, not likely to find any other vintage non 650b bike that takes so well to being converted. I did have the rear stays cold set to accept a modern 9 speed 135mm hub and that was it. If sticking with say 7 speed the 126mm stock spacing should suffice. Having one modified to accept canti brakes as well as rack mounts would make it all the better. I still might have it done and get a repaint in the same factory color one day just to get away from the clamps on the fork, makes it much tidier. All one really needs are the Dia Compe 750 center pull brakes.
The only real "problem " is finding a good example in one's size, mine is a 56 cm. I check from time to time but they tend to be few and far between, so if anyone has a chance to buy one locally do not wait too long. The models from 1979 - 1982 will have the same geometry with a nice low trail, 1981 - 82 have the braze on cable guides on the top tube. It is possible that earlier S10S from the mid '70's and on are the same but I believe they have an all hi tensile frame. No doubt they ride well, just heavier which might translate to a less agile feel and handling. I really like the thin seat stays on the S12S as well.
I would suggest if mounting fenders to go with stainless steel, a bit heavier but not prone to cracking as the aluminum ones are. I have a pair from Velo Orange on mine and due to simply drilling a small hole and mounting it with an L shaped bracket at the rear brake bridge it eventually broke in two at that point after a few years. Mind you I made the mistake of not using a leather washer to isolate it. I rode the bike on quite a few gravel trails so there was most likely more vibrational stress introduced, the more damaging high frequency kind. Using a bracket that crimps around at both sides around the fender edges would be a better choice there, though less clearance at the tire side wall. Use larger washers as well at the back stays and front chain stay bridge.
Last edited by VintageRide; 02-10-21 at 04:56 PM.