Mine are ~50cm. Reckon I could shave a couple of cm's off that, but no more. You lose too much leverage and ability to sprint from slow speed or get a fast start from a stop when you go too much thinner than your shoulder width (that's me anyway). That's much more important to me than squeeking through traffic with crazily narrow bars. I think a lot of people go super-thin due to fashion rather than function.