Sizing a rider on a smaller frame means that the headtube will be shorter so the saddle to handlebar drop is greater. At 6 ft tall a 56 might fit but more than likely it’s small. At 6’1” my perfect size is 59/60, and a 62cm isn’t too big. 58 is the smallest I will ride.
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Vintage, modern, e-road. It is a big cycling universe.