BikeCAD uses the threadless stem standard for defining stem angle. To measure the angle of a stem, we place the stem on a horizontal surface and measure the angle that the stem rises above the horizontal. Because most treadless stems are reversible, a stem with a 10° rise could be flipped around to serve as a stem with a 10° drop. In BikeCAD, a stem with drop could be attained by assigning a negative value to stem angle. Some examples of stem angles are shown below. Notice that in the example on the right, although the stem is now mounted on a bike with a 73° head angle, the stem angle is still measured as though the stem collar is placed on a horizontal surface.
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