anyone know the top tube length C-C on a 52cm '85 ironman? what sizes were they available from between 49-53cm? by 2cm increments?
Not 100% sure.
But, ST increments were in
even sizes, as far as I know. Centurion measured funny, but basically, from the c-bb to the t-top tube, on the Ironman frames. They actually called it "to the lowest part of the scallop on the side of seat lug." Visually, this is about the same as the top of the top tube.
I've heard it told of 61cm Ironman frames, and a certain lady who raced for them had a 49cm Ironman frame, but there is no way of knowing if the 61cm "factory" frames were mismeasured, or the 49cm frame was even an Ironman frame. She wasn't racing for them when her frame's color scheme came out.
Now, the frames were pretty square at 54cm and 56cm. As they went up from 56 in 2cm increments, the TT seemed to go up about 1cm each time. As they went down from 54 in 2cm increments, the TT seemed to go down about 1cm each time, but I've never measured any of the smaller ones.
My experience is that my 56's were square, and my 54's had to be close to that, because I probably could have gotten by on a 54ST/55TT, but they were just way too short, so I'm assuming they were 54TT, as well.