Because they don't need gasoline, petrol or electricity. If you use a bicycle instead of a car you have a zero carbon footprint for that journey.
"We have green bicycles."
Yellow monkeys wear blue hats. Therefore, green monkeys wear purple hats and GREEN MONKEYS ARE AWESOME. They are so cute when they ride the little bicycles at the circus...
If the bicycles belong to ONE FRIEND, it's "friend's bicycles." If the bicycles belong to TWO OR MORE FRIENDS, it's "friends' bicycles."
1.8 bicycles.
There is no specific collective noun for bicycles, in which case a noun suitable for the situation is used, for example a rack of bicycles, a row of bicycles, a standof bicycles, etc.
Bicycles weren't invented in Canada.
what did the ancient bicycles look like?
More bicycles
Bicycles Are for the Summer was created in 1984.
Diamondback Bicycles was created in 1978.
Giant Bicycles was created in 1972.
The first bicycles were powered by humans.