

An aero road bike might mean an extra narrow bar, while a big tire gravel bike might mean an extra-wide bar.

Modern bike fitting recognizes it's far more complicated than that, and different types of bikes make it even more complicated. Old-school bike shop wisdom is to measure your shoulders and use that width to match up a handlebar. Once you understand how the measurement is defined, you have to decide what to get. Some companies mix things up and do it differently though. With gravel bars, that doesn't typically make sense due to the flare, so it might be center to center at the hoods. Sometimes it means center to center from the end of the drops. One of the things to check with handlebar width is how the company you are researching measures it. The first set of numbers you'll need to make decisions about are the same as road handlebars.

If you do want a bigger flare, there is also a 30-degree flare option. It doesn't cost much, it's easy to get, and with a 12-degree flare it's enough for stability but not so much that it puts your arms in an awkward position. If you like the idea of a perfectly straightforward option, then Shimano's Pro brand has something for you. Not everyone needs a wacky, expensive and weird handlebar.
