Thanks again for the extensive comments... They are all very useful to me.

In terms of stability, I would suggest that the feeling of stability I described was a consequence of the shorter distance between the tyre and the hub on a brompton. It's the same feeling I get riding my scooter as opposed to a proper motorbike. Almost a top-heavy feeling and a tendency to weave more. In engineering terms I think the flywheel effect and to a lesser extent, the gyroscopic effect of larger wheels does make a difference. At the same time, I am very impressed by Bromptons, so don't think of me as a Brompton-Hater

I agree that the statement I made about people 'using large wheels since the dawn of time' was a little backward-looking. I felt that a bit as I was writing it, but left it in anyway to guage the reaction.

I disagree that bicycles are in a state of stunted development. I think any frame-builder or bike designer embarks upon a process of evaluation before beginning work. In many respects this could be considered an evaluation of human-powered transport. I certainly embarked upon - and indeed still consider myself to be in the process of - an evaluation of human-powered transport.

My ideal situation would be a bike that can be carried in a backpack and could accompany anyone on a trip anywhere as the sole method of (land) transport, irrespective of terrian, and be equally at home in a car-boot or overhead rack on a train. You can start at any point in this design and will still arrive at something resembling a regular bicycle. Not because I'm backward-looking or basing my decisions on flawed engineering and prejudice, but simply because it is a well-evolved compromise between all the essential needs.

thanks again for your posts