Interesting, only 1 billion bicycles? I would have expected more than that. In most of the places I lived (Europe, Asia) there seems to be more than one beater bike per person lying around somewhere (and some nice bikes, too, but much fewer).
I'm actually surprised it's 1 billion, when you remove children, elderly, people simply out of shape for a bike, people unable to afford a bike no matter how cheap, people with disabilities incompatible with bikes, that billion is like 75%+ coverage of TAM.
Is that 1 billion adult bikes in particular? Because in the US, anywhere outside of big cities or college towns, children are ALMOST the only people who ride bikes regularly.
Many (most?) children have bikes, and lots of elderly people have some bikes somewhere in a shed back from when they used to be able to ride.
Almost everyone can afford a beater bike. That's why they are so common in the third world.
I'm not sure how out of shape you need to be not to be able to ride a bike? In any case, I wasn't wondering about how many people actively ride bikes. I was wondering how many bikes there are.