Handlebars are predominantly set to your comfort level but keeping some things in mind. The goal is to get your handlebars to be at the same height as your seat. That will require core strength so that you can maintain your torso in a hinged position of about 45 degrees with your chest lifted. If you have a bad back, make sure the handlebars are high enough so that you’re not straining your back and slowly work your way down. It’s important to be conscious of your back when riding. Once you find a comfortable position, take note of the number on the handlebar post so it’s easy to adjust your bike next time and tighten the knob.