My 80's road bike has, I believe, a 38 bar. It's too narrow for me. Probably weighs as much as some people's bikes, so I don't think you want it
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I generally ride a 42, it's a comfortable fit for me. So send me your old one
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I've sometimes wondered if they used to use narrower handlebars to make it easier to balance with one hand while you're operating the downtube shifters. Maybe this is a completely stupid idea though.