Because the technology is changing so quickly so too is the mountain bike fit. As more handlebar options become available one aspect of a mountain bike fit has gotten increasingly important — with some mountain handlebars, getting the proper arm position can be difficult.
Once the reach is settled we come to the most important factor to attaining the proper arm position: the amount of bar sweep.
What is bar sweep? It is the amount the bar bends back towards you. You have probably seen bars that have rise built into them – that’s when the bar bends upward to raise the hand grip position. The bend to increase sweep happens in a different plane to bend the bar back towards the rider so the hand grips are no longer pointing directly out to the sides, they’re pointing slightly back towards the rider.
Most modern bars have some sweep built into them — roughly 3-10 degrees exists on most bars these days. But others bend aggressively to 20, 30, or even 45 degrees of sweep like the Answer 20/20, an H-Bar, or Seven Tiberius (among many others).
Why would you want the bar to bend back toward you like this? Simple. It allows the wrists to sit in a more neutral position, it allows the elbows to drop down to the 7 o’clock/5 o’clock position which gets the lat muscles involved and relaxes our shoulder posture.
This will lead to long periods of very stable and comfortable upper body positioning on your mountain bike.
A safe rule of thumb is that as the sweep increases so should the amount of easy cross-country riding you do. So if you are riding on aggressive terrain you will likely find a bar with more moderate sweep angles (in the 5-15 degree range) more to your liking because although the added sweep is very neutral and “relieving” on easy and moderate terrain, a straighter bar provides more of what I call passive resistance to some of the more extreme inputs that come through the handlebars on aggressive trails. Having the hands and wrists closer to the more traditional mountain bike handlebar position may make you feel more powerful and in-control. The passive resistance we see in a straighter bar comes from a locked (or close-packed) wrist position, a straighter elbow and an elevated shoulder blade and glenohumeral joint — all are relying on a skeletally-locked posture but come with a price of potentially increased risk of joint irritation (in the wrists, elbows, shoulder and neck) and soft tissue strain.
So experiment a little and figure out what works best for you depending on your preferred type of riding and what your body is telling you. You might find that a bar with a few degrees more or less of sweep will work for you.