If you're a long time bicycle commuter, you probably have some
appreciation for a bike that performs well, and that is where the
Bike Friday will shine. I have owned a Dahon and two Bike Fridays
(just traded in my New World Tourist for a Crusoe). The Dahon was
one of their top-of-the-line models of a couple years ago: aluminum
frame, great components. Dahon definitely has great folding
technology -- you can fold their small-wheel bikes incredibly fast.
I had opted for an 8-speed, and that was a fine range for Boston.
However, the sizing of Dahons is awkward. Though their Web site
claims that their bikes fit a huge size range, they definitely don't
fit everybody in that range properly. Moreover, the wheelbase is
overly long (to accommodate their folding tech), which affects
handling. I've been cycle commuting for almost 20 years, and I took
two spills on the Dahon when it didn't behave like a "proper bike"
should.

The Bike Fridays are really nice to ride. They've simplified the
folding a bit on their newest models (no need to turn the front
wheel), but it is undeniably slower and more awkward to fold than the
Dahon. That said, I think you could get the process down pretty fast
(in the 1 minute time zone). For ruggedness, I don't think you have
too much to worry about. Small wheels are actually stronger than big
wheels, and you could customize in any way you like when your bike
design is worked out (for example, I have extra-strong rims and
Kevlar tires on my bike). For the frame, there are plenty of
options. I'm sure a New World Tourist frame would be sufficient, and
probably a Crusoe too, unless you're doing crazy bumpy riding
perhaps. My new Crusoe came in under 20 pounds (without pedals and
saddle), and it is a real delight to ride -- very responsive and
speedy.

For carrying on the T, you'll definitely need a bag. The bags (we
have one for our Bike Friday tandem) are pretty easy and fast to
use. Keep in mind that your bundle will not be fun to negotiate
through a packed Green Line trolley, but it will definitely be
possible to take it with you.

Good luck!

Fritz Knabe