Thanks for those replies!
Which reminds me of a related question. I have 9,000 miles experience with 16" wheels (ISO 305) but only limited experience with Brompton/Moulton/Tiket sized 16" wheels (ISO 349); and 6,000 miles experience with 20" wheels (both ISO 406 and 451). 20" tires last a lot longer, and get far fewer flat tires. Am I mistaken about that? Anyway, this makes me reluctant to go back to 16" wheels.
Hey Rhm ... good to see you around again.
Brompton, Bike Friday (tikit and standard models), and some Dahons (all 20" models from memory ... the Speed series is steel) have steel frames. Yes Moulton ... although you should realize that the size is ERTO 369 ... or something like that ... for some of their models.
349 is considerably larger than 305. Nonetheless, for tires of the same construction, you will get considerably more miles out of a 20" tire. Although I recall getting a lot of miles out of a 349 Marathon if that is a tire that fits your riding. I don't remember getting more flats with smaller wheels.