I'm trying to cold set an early 80s Schwinn Super Sport from 120mm to 126mm rear spacing. This is the second frame frame I've cold set. The first was a mid-80s Conti which was easy peasy. Spread the spacing to about 144mm with threaded rod and nuts and it relaxed back just about where I intended at 126. I tried the same technique on the Super Sport, so far with no luck. I used the same threaded rod/nuts/washers to open the spacing to 144mm and let it sit for a couple days. Here's what my setup looked like. It's not real obvious from the angle of the shot, but the threaded rod has a couple fender washers inboard of each dropout and nuts inside of them. I just crank them out until I reach the desired distance, tap in the board and clamp it to the rod (to keep it from going anywhere), make sure the clamps on the stays are nice and snug, then go do something else for a day or two.



I'm skeptical the clamps ahead of the two bridges had any real effect, but they made me feel better. The board tapped in between the chain stays was to encourage some of the bending to happen a bit further forward. Also probably unnecessary.

After two days, I undid everything and measured. It relaxed back to 121mm. Hmmm... I went a bit further, to 146mm, and let it sit another day. Still 121mm after that. Finally, yesterday, I widened the nuts to take the spacing to 152mm. Checking this morning, I found it relaxed back to 121mm again. I have clearly so far not exceeded the elastic limit of the stays.

The sticker on the seat tube says it's Tange Champion No 2, which I think is pretty generic 4130 steel, not hardened, correct? I'm guessing the chain stays (and seat stays?) are just really stout. How am I going to get this rear triangle spread to 126mm without breaking the brazed joints at the brake bridge or chain stay bridge? Are my clamps improving the chances that when the stays finally move that those joints remain intact, or am I just fooling myself?