I used folding bikes exclusively for about a year, and did several tours, numerous "metric centuries" (60+ miles) and an "imperial" century (100 miles) on folders.
In general, I do not recommend most folders for century rides, but it can definitely be done, and it's OK if you meet a few critical requirements:
• You find the folder to be
very comfortable on longer rides.
• The century you're going to do is flat, OR the folder has very wide gearing.
• You're sure your folder is in excellent mechanical shape.
• You don't make any major changes to the bike (or change bikes altogether) shortly before the century.
There are only a few high-end folders/separatables I'd recommend for 100 miles. A well-fitted and properly geared Bike Friday; just about any Moulton; maybe a Pacific Reach. Others can be used but only if you really, really, really aren't bothered by road buzz and don't need a wide gearing range.
I
would point out that I do a lot of distance riding and vastly prefer 700c bikes, but that might not fly 'round here...
