Road bars come in a variety of widths, from 36cm wide up to 44cm, a good guide for bar width is your shoulder width, a bar should not be narrower than your shoulders as this can close up your chest, but they should not be so wide that you are creating a large frontal area. Road handlebars come in two clamp sizes, 31.8mm which is oversized and 26/25.8mm which is standard, it is essential that you get the correct clamp size for your stem as a poor fit will slip round. Road bars also come in different shapes and depths, with various bends for ergonomic reasons, some will also feature grooves in the material for your brake and gear cables to slot into, this helps to keep the bar round once tape is applied.