The stem is one of those invisible parts on your bike that can have a huge impact. Handlebar stems come in all shapes and sizes, and for good reason. The length of your stem, together with the angle at which it is positioned, largely determines your posture. If you want to adopt a more sporty position on the bike, you should opt for a longer stem, which allows you to sit slightly more bent over on the bike. If you really want to sit aggressively, lower the angle of the stem as well. Are you going for a more comfortable position? Then choose a stem with a higher angle and a shorter version. Or you can choose one with an adjustable angle so you have more options.