Part 1 – The Fitter
When considering bike fitting tools, the first question to ask is: “Who is using the tool, and for what purpose?” That “who” generally falls into two groups: professional fitters and cycling enthusiasts. Each group uses tools with different goals in mind.
This first post focuses on the tools professional fitters use. In Part 2, we’ll look at what enthusiasts should consider when selecting and using tools to fine-tune their setup.
The Professional Fitter's Toolkit
A professional fitter begins by understanding the client’s cycling history and future goals—both general health and sport-specific. This foundation guides every measurement and adjustment that follows.
Key Body Measurements (Tools Required):
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Height
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Torso length
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Shoulder width
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Arm length
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Leg length (divided into femur and tibia)
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Sit bone width (critical for saddle selection)
Additional Assessment Factors:
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Fitness level
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Physical limitations (injuries, flexibility, etc.)
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Riding style (commuter, road racer, triathlete, etc.)
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Cycling goals (casual riding, endurance events, performance racing)
With this information, the fitter adjusts the position of the rider’s contact points pedals, saddle, and handlebars to optimize comfort, efficiency, and performance.
How the Rider Inputs are Applied to Determine Position (Fit)
1. The Fit Bike
A fit bike is a specialized, adjustable stationary bike used to simulate and fine-tune the rider’s ideal position. Advanced models include integrated measurement systems that provide real-time data on saddle height, reach, and stack—making precise adjustments easier and more accurate.
Below are three fit bikes using somewhat different approaches to adjusting the relationship between the rider’s sit bones, hands, and feet.
2. The Rider's Bike
The final step is transferring the optimized position from the fit bike to the rider’s actual bike. This might happen during the fitting session or later, but the critical point is maintaining the relative position of the three touchpoints.
Precision matters: Serious riders often notice a misalignment of just a few millimeters. Casual cyclists may tolerate greater deviation—but accuracy and repeatability are always better.
Coming Up in Future Posts:
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Part 2: How fit measurements are defined with the traditional X-Y convention.
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Part 3: Comparing the traditional approach with the new Dupli-Fit point-to-point method
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Part 4: Comparison of Dupli-Fit’s direct measurement method with traditional X-Y coordinates
Which Bike Fitting Tool is Right for Me? It Depends on Your Needs
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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B: 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 horizontal (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!