I found this article about the history of the Brompton:
The thing I find so interesting about it is how many different design aspects I view as distinguishing features of other folders that were rejected by Ritchie for one reason or another:
- Fold-under front wheel (Birdy,Mezzo)
"In Ritchie's first prototype design (P1)...the front wheel of P1 also moved (almost) in its own plane underneath the bicycle to sit alongside its partner; in this case some sideways movement was needed to ensure that the front wheel sat next to the rear one, rather than just bumping against it as it hinged. To achieve this the front wheel needed a complex, skewed hinge to move it the few inches sideways so as to clear the rear wheel and chainwheel."
"The major design difference between P1 and subsequent prototypes was the removal of the complex skewed hinge required to move the front wheel in its own plane underneath the bicycle to sit alongside the rear wheel."
- Larger wheels (Dahon, Bike Friday, etc)
"Prototype P1 used 18 inch wheels, then common on children's bicycles."
- Custom wheels (Carryme, Strida, IF Mode)
"Two more prototypes were built...this time with 16-inch wheels. Wheel size is a key issue for the designer of a folding bike. Smaller wheels are easier to pack small, but the smaller the wheel the bigger the pothole feels! There is also the ‘make or buy’ decision to consider. Mass production of bicycle wheels is a big issue; it is much easier for a manufacturer to buy-in wheels produced by a large manufacturer than to dedicate machinery and labour to the production of wheels just for their own product."
- Automatic fold (Tikit)
"Bowden cables linked the front- and rear-wheel folding mechanisms."
- Folding cranks (none, but I've thought it'd be an improvement)
"The craft route to producing the [folding] pedal involves 64 operations. The company bought a piercing and blanking tool for £3500 in 1991 to reduce these operations. All the earlier prototypes and the first batch had a folding crank."
"It was a clever eccentric mechanism that wore easily."-Ritchie(1999)
- Custom drivetrain (Carryme)
"Gearing was always a problem. To most manufacturers the folding bike is a bottom-of-the-range product. We wanted proper gearing using a bigger-than-average chainwheel, so at various times we became involved in making gears, for example a 13 tooth rear gear. And we had problems with broken teeth. Things are better now. We use the 3 and 5 speed Sturmey Archer hub for gears."-Ritchie(1999)
- Derailleur gearing (Dahon, Bike Friday, etc)
"We have resisted the complication of Derailleur gears. All that extra complication is against the philosophy of the design."-Ritchie(1999)
- Bring saddle closer to chainwheel (Dahon Curl)
"…it was too complicated, I gave up an inch when that idea was dropped."-Ritchie(1999)
- Aluminum (Dahon, Merc, Pacific, etc)
"Aluminium is too soft for a folding bicycle, it just doesn't stand up to the knocks, the everyday wear and tear."-Ritchie(1999)
"There are many design routes to producing a lighter frame or a more easily manufactured frame that are not available to a small batch manufacturer. He had to use soft, mild steel for the main tube as he could not bend stronger alloy steel, and the main tube had an aesthetically ugly kink from the bending process....The process is essentially scaled-up craft production."
"The drive to design for manufacturability continues apace. A tool was designed to curve the main tube, so removing that kink. At the time of writing, 2000, a power press allows the use of a higher specification of steel for the main frame member. The hinges were machined from the solid until expensive forging tools could be bought in 1987. Ritchie is working on removing the skill from the manufacture of hinges."
- Commercial Success (Dahon, Bike Friday, Brompton, etc)
"Ritchie was driven by a search for ‘the ultimate in compactness’ when designing and building P1, which was a platform for various design ideas."
"Ritchie uses the expression ‘good luck rather than design’ to describe unpredicted advantages of his conceptual design solution."
"Ritchie, an old Harrovian who read engineering at Cambridge, is 35 and says he is appalled by the amount of his life he has already given to this bike."
"Bending one top tube is difficult enough, bending fifty is really tiring."-Ritchie(1999)
"Perhaps we could sell another thousand bicycles. It's what the market wants. It's a luxury, but we do not respond."-Ritchie(1999)
"Bicycles designed to be folded into a convenient shape have a long and honorable history going back at least as far as 1885....Common to all these designs (and the Bickerton) is the problem of the protruding chainwheel, so Ritchie's concept looks to be a genuine innovation."
Amazingly good idea, the Brompton, (and built to high standards too) but it's also amazing how much innovation the company missed out on simply because they didn't have the skill or willingness to make it work. Still they've done a lot more than me with my armchair folding bike ideas.