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The title says it all. Are the two rotations of MTB flat bars (question updated in italics) called "upsweep" and "backsweep" because only one quadrant is usable?

Is there never a scenario when you might prefer "frontsweep" as a (temporary or permanent) way to solve a stem-too-short-for-my-liking problem?

Is there never a scenario when you might prefer "downsweep" if the stem angle is too high?

upsweep and backsweep

(Please don't just answer by saying "the angle at the grips will not be right". I'm asking because I'm seeking an expert opinion, and I suspect this is—as with most bike issues—a subtle one.)

Related question for road handlebar
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  • I'll elaborate later with an answer, but front sweep would put your arms (and especially your wrists) in quite an awful position.
    – MaplePanda
    Commented Oct 10, 2022 at 17:41
  • @MaplePanda The two terms don't mean what I wrote; do they? One is a built-in property of the handlebar, and the other is the unique variable (rotation angle once in the stem) to install the handlebar. Can you clarify? Also, the angle of installation is partly a function of the width of the shoulders of the rider. Indeed, the rider would have to have unusually wide (i.e., non-existing) shoulders for frontsweep to be used.
    – Sam7919
    Commented Oct 10, 2022 at 18:32

3 Answers 3

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Okay, let me begin with some terminology clarifications:

  • Sweep is an angular measurement, not a linear one. For example, your bars may have an upsweep of 5°, not 20mm. This is an important distinction because it affects the directions your bar grips point at in 3D space.
  • Backsweep: the angle the grips point backwards at. This is distinct from upsweep since handlebars have a compound bend. It's inaccurate to model them as a simple V. enter image description here
  • Upsweep: the angle the grips point upwards at. Note that this is not the same thing as the bars' rise. enter image description here

Now, you can more or less model the range of motion of your outstretched arms as a semicircle. Imagine the handlebar has no backsweep; it can be modeled as a tangent line at the apex of the semicircular arc. I will add a diagram when I can, but you might be able to visualize how when spread apart by the handlebar's width, your arms will meet the ends of the handlebar line at an angle (they form an isosceles triangle). Adding some backsweep to the bars makes them follow your arms' range of motion better, since the grips will be closer to tangential with the semicircle. Hence, in my comment I noted that front sweep would be unpleasant because it would make your arms meet the bar at an even less perpendicular angle than a straight bar would.

The same argument more or less applies for justifying upsweep. Since humans generally have torsos, their shoulders are raised above the vertical level of the stem. Hence, your arms meet the handlebars at an angle in the z-direction, which upsweep compensates for. Like before, downsweep would make your wrists have to bend excessively to adjust for the angular misalignment between your arms and the bars.

enter image description here

Overall, I'd argue that yes, only one quadrant is usable. The angles are just nonsensical in the other three. Additionally, for high-end, lightweight bars which may have an asymmetric internal construction, it might be bad for them structurally speaking to be loaded in directions they were not intended to be used in.

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  • Although this is heading towards an excellent answer, I'm still unsure. It seems one is intrinsic to the handlebar and the other is not. Say you're at a shop and the seller doesn't even see your bike. From your diagrams it sounds like it would make sense to ask the shopkeeper "what is the backsweep of this handlebar?", but that it only makes sense to talk about "upsweep" after choosing the handlebar's angle in the stem; is that right?
    – Sam7919
    Commented Oct 12, 2022 at 13:14
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    @Sam Incorrect (generally speaking). For bars with distinct up- and back sweep values, they are both intrinsic to the bar. When the bar is oriented such that its rise is perfectly vertical, it will have a distinct up- and back sweep. If the shopkeeper talks about a “0° rise, 5° back bar”, I know that bar will have no upsweep when the rise is nominally oriented.
    – MaplePanda
    Commented Oct 12, 2022 at 15:58
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If you wish, you can rotate most handlebars to opposite the "normal" positions and experience down/forward sweep in real life. You will probably find you do not prefer these configurations, hence naming the dimensions after the most common installations.

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I think you'll find that drop handlebars have exactly the opposite:

  • They have frontsweep, only it's called reach now
  • They have downsweep, only it's called drop now

So the claim that only upsweep and backsweep would be useful is false.

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  • Apologies.. I didn't write that I'm specifically asking about MTB flat bars at this time. Fixed. Did you click on the video link?
    – Sam7919
    Commented Oct 10, 2022 at 16:33

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