This folding sociable tandem bike was parked near one of the lakes in Beijing. The bike seems to have been modified so that it no longer has a drive train. Perhaps its now used as some kind of tricycle wheelchair. It looked to me like it could have had two bottom brackets for a twin set of pedals and chains, two seat posts and linked handlebars. I can't imagine it would be easy to reach the steering wheel from sitting in the padded seat/cargo rack, so it must have had a different set of handlebars when it was new.

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Just around the corner there were three- and four-seater tandem bikes for rent. Does your bike have lumbar support like this?