Part 2 – Fit Measurements Using X-Y Coordinates
In Part 1, we looked at how professional fitters assess a rider's needs and make adjustments. Now, in Part 2, we’ll look at how the rider’s three contact points are commonly measured and defined.
Defining Fit Points with X-Y Coordinates
Using a fixed reference point—usually the bottom bracket (the pedal axis)—fitters measure the relative location of the three key contact points: saddle, handlebars, and pedals – See Figure 1.
Point A: Bottom Bracket (Crankset Axis of Rotation)
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This is the zero point from which all other positions are measured.
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Why not start at the pedal? The bottom bracket is easier to locate precisely and is universally used to describe frame geometry.
Point B: Saddle
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There's no universal standard, but common reference points include:
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B1: Midpoint of saddle length
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B2: Saddle tip
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B3: Point where saddle width is 80 mm (matches sit bone width for many riders)
Point C: Handlebars
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Traditionally, the centerline of round handlebars was used as the reference.
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More aggressive riders may use C2: the shifter grip hollow.
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Modern handlebars made from composites often have unique shapes and are sometimes integrated with the stem (aka “cockpit”). These designs improve aerodynamics and stiffness, but limit adjustability and complicate finding consistent reference points.
The relative position of each is defined by the horizonal (X) and vertical (Y) distance from the Bottom Bracket, generally measured in millimeters.
In Part 3, we’ll look at how Dupli-Fit rethinks this traditional model—offering a new method for defining and transferring rider position. Stay tuned!