I had heard rumour of the Titanium model several years ago. It was said to be much more expensive than a conventional Al frame and turned out to be no lighter (the 2011 Titanium model is listed at 11kg despite high end components) - so the original project was shelved. Perhaps they were wondering how to shift a few hundred spare prototype Ti frames. . ?

It is noticeable that the Birdy has put on quite a bit of weight over the years (unlike the Brompton which got lighter). I have reference to the first Birdy Blacks from 1997 weighing in at 8.7kg (~19 lbs). But there were weak points, like the seat clamp, and complaints of creaks, squeaks and fatigue cracks. Does anyone have a list of important changes? I know the front swing arms were changed before the seat clamp and expedition rack mount points were added. Presumably these and other monocoque frame improvements will be captured in the new World one too.

The classic frame shape has remained surprisingly popular, as evidenced by prices those older bikes still fetch on Ebay. The new World frame may just be a way to capitalize on that - and perhaps benefit from higher build volumes - they only offer one colour for each model and few accessories but claim they will be sold world wide. Could be cheaper to make than the mono too – less welding. Perhaps they plan it as a market probe before switching higher spec’d models to the new frame? It will be interesting to learn more once the new bike is properly launched.

However, to my mind the question remains: Why bother changing from the Classic round top tube to a more boxy triangular one? Is it cost, function or a Germanic perception of aesthetics?