yea, step 1 .. have only bought the bike in the last year.. so it's the new spider crank,
as the other previously , the chainring is swaged on to the crank.
I like Surly's stainless steel rings on single speed drivetrains .
not even much weight penalty in a 130-39t size
[I see measuring weight was the first highlight.]
and they can be flipped over to wear twice as long..
flat S-A hub cogs you can do that too .
Yes, this is only useful for 2013 and later B'tons.
But some folks with other folders that has a spider
crank might find this info useful. Thanks for the
info on Surly chain rings; will check them out if
they have the right BCD. And don't worry, if you
have a 2012 and earlier Brompton - I still got you