Vietnam war: reinforced bikes to carry artillery?

Recently I've read a couple of book about the
Vietnam war(s) and more than once I've read
that the Vietnamese for transport during their
anti-colonial and independence struggle used
"reinforced bikes" ("förstärkta" in Swedish
which is either "reinforced" or "amplified",
I think).

On such bikes they would carry all but
everything, including big guns, like artillery,
to bombard the French and the Americans.

I wonder what they mean exactly by
"reinforced"? Was that something the guerillas
did provisionally in their cave workshops or
did the reinforcement happen in factories in
China or someplace else?

And how do you reinforce a bike to carry an
anti-aircraft gun? Put on an extra top tube and
give it a 40-spoke rear wheel?

And do you actually ride this bike, or more
likely probably you just walk by its side with
support wheels, pushing it forward until dead
tired when the next guy takes by?

--
underground experts united
http://user.it.uu.se/~embe8573