Handlebars are the steering mechanism on a bicycle. Handlebars connect via the stem to the fork, allowing the rider to steer and balance the bicycle by turning the front wheel.
Components such as brake levers and shifters are often attached to the handlebars and many riders attach additional accessories such as lights or cycle-computers to their handlebars as well.
Handlebars are available in a wide variety of shapes and configurations. Choosing, replacing or adjusting the handlebars allow a rider to make significant changes to the way a bike fits, handles and looks.
There are a wide variety of handlebar designs, each offering a unique balance of riding posture, hand position, maneuverability, comfort and style.
Flat handlebars are just that: a simple essentially straight bar. Both flat and riser handlebars are common on mountain and hybrid bikes and create a fairly upright riding position compared to most road bike handlebars.
The "grips" on a flat handlebar are aligned parallel to the ground and perpendicular to the main axis of the bike. Flat bars are generally wider than most road or drop handlebars, although some riders create custom "chop" bars that are extremely narrow, sometimes no wider than grips themselves.
With a flat bar, ignoring the brake levers, shifters or accessories, riders can place their hands essentially anywhere along the length of the handlebars, although the levers are usually positioned to be with easy reach from the ends of the bar.
"Bar end" attachments, which are short extensions bolted onto the ends of a bar to provide additional riding positions and hand placements, are sometimes used with flat and riser bars. Although once quite common the popularity of bar ends has waned significantly from the mid-to-late 1990s peak with the rising popularity or bullhorn and comfort bars which offer similar hand positions without additional attachments.
Riser handlebars are a variation of flat bars that have a slight (or in some cases, large) bend that displaces the center part of the bar relative to the grips. This creates a more upright riding position.
Like flat handlebars, riser bars align the grips more-or-less parallel to the ground and perpendicular to the main axis of the bike. As with flat bars, with a riser handlebar riders can place their hands anywhere along the bar although the levers are usually positioned at the ends.
BMX-style handlebars have a much larger rise than most riser bars but still position the grips largely parallel to the ground and perpendicular to the main axis of the bike. BMX bars tend to use a cross-brace to provide additional rigidity and strength, resulting in the iconic trapezoidal shape often seen on BMX bikes.
Upright handlebars (sometimes known as "north road", "comfort" or "cruiser" bars) feature both a significant rise and grips that sweep back toward the rider until they are nearly parallel to the main axis of the bike. While far from aerodynamic, upright handlebars provide an upright riding position, wide stance and relaxed steering that many riders appreciate.
Upright handlebars were common on classic European three-speed roadsters and have enjoyed a resurgence on modern cruiser, comfort, utility and "city" bike designs.
Drop (road) handlebars, frequently seen on performance oriented road bikes, have backward-"C" shaped ends that slope first down and away from the rider and then back toward the rear of the bike (ending parallel to the both the ground and the main axis of the bike).
Drop bars are popular on road and touring bikes due to their aerodynamic riding position and to the variety of hand positions they offer. With drop handlebars riders can position their hands "on the tops" at the center of the bar for an upright posture or "in the drops" at the bottom of the curve for a more aerodynamic riding and to shift more weight toward the front of the bicycle. Many bikes with drop handlebars use brake and shifting levers mounted along the outside of the bend, offering a third hand position "on the hoods" for a more stretched out posture. Typically road handlebars are wrapped with tape or cork to provide a comfortable grip anywhere along the bar.
Some riders are intimidated by riding in the drops, in part due to the low and forward riding position it creates and since the brake levers aren't always within easy reach from this hand position, but drop bars are actually quite easy and comfortable to use once you are used to them. Many riders find that the parallel position of the grip offered by upright, drop, bullhorn and other handlebar types is more natural and comfortable than the perpendicular orientation of flat and riser bars.
Drop handlebars tend to be narrower than the flat bars used on mountain or hybrid bikes. As a rule of thumb, drop handlebars should be about the same width as the rider's shoulders.
Drop handlebars vary somewhat in the exact shape used in the curve of the "C". Traditional drop bars use an essentially continuous radius curve, resulting in a semi-circular bend before flattening out at the bottom of the drops. Others, known as "ergo" (for "ergodynamic") or "anatomic" bars include a flat section along parts of the curve.
(If you imagine the profile of a drop handlebar as the face of a clock, a traditional drop bar will having a continuous curve from the 12 to the 6 while an ergo bar will flatten out the part of the curve from the 3 to the 6 to be a straight line approximately one hand's width long at a roughly 60° angle.)
Ergo handlebars are meant to provide a comfortable hand position along the inside of the curve. Whether they achieve this goal is question of fit and depends greatly on the specific rider, the specific bar, and how that bar is adjusted relative to other components on the bike. Some riders swear by ergo bars, others find the continuous curve used on traditional drop bars more comfortable and versatile.
Many road handlebars have one or more grooves designed to help route brake or shifter cables beneath the cork or tape wrapping. While not strictly necessary, these grooves can help hide and smooth over cables routed beneath the tape.