Four dimensions determine how a handlebar performs: clamp diameter, width, rise and backsweep. Material and finish come after. A change of handlebar is felt immediately, far more than a stem change.
The clamp diameter, to check first
31.8 mm : the standard, compatible with the vast majority of stems.
35 mm : stiffer, found on recent enduro and downhill handlebars.
The two are not interchangeable : the handlebar and the stem must have the exact same diameter.
25.4 mm remains on older MTBs and certain kids' bikes.
The width
700 to 740 mm : cross-country, compact and aerodynamic position.
760 to 780 mm : trail and all-mountain, the most common range today.
780 to 800 mm : enduro and downhill, for leverage and high-speed control.
Too wide, the handlebar opens the chest and fatigues the shoulders; too narrow, it makes the bike twitchy and imprecise.
A handlebar can be cut down by a few millimetres on each side, but never beyond the manufacturer's cut marks.
The rise
0 to 20 mm : cross-country, low and forward-biased position.
25 to 40 mm : trail, the most common compromise.
40 to 50 mm and more : enduro and downhill, to shift body weight rearward.
Rise combines with spacers and stem angle: it is the complete assembly that determines the actual handlebar height, not the handlebar alone.
Backsweep and upsweep
Backsweep, or rearward angle, is the most underestimated adjustment on the cockpit: it determines whether your wrists are aligned or in permanent torsion. Common values range from 7 to 9°, and 8° suits the vast majority of riders. Beyond 12°, you enter the realm of comfort and bikepacking handlebars. Upsweep, the vertical rise angle, ranges between 4 and 6° and is felt much less.
Aluminium or carbon
Aluminium : absorbs impacts, bends rather than snaps, and is inexpensive to replace.
Carbon : noticeably filters vibrations and saves 80 to 150 g. On the other hand, a carbon handlebar that has suffered an impact must be replaced, even without visible damage.
Respect the torque setting to the Newton-metre, on the handlebar as well as the levers. It is the part on the bike where overtightening is the most dangerous.
