Understanding the Increasing Complexity of Choosing the Right Bike and the Growing Importance of Bike-Sizing Today.

Frame sizing can vary between brands due to two main factors:

Morphological Proportions: Cyclists with different body proportions, such as long legs and a short trunk or vice versa, may find a better fit with frames of varying sizes. This is why a cyclist of 1.80 meters could potentially ride a frame ranging from 54 to 58 (S-XL).
Measurement Methods: The numerical or alphabetical value assigned to a frame size is measured differently by manufacturers. With the introduction of sloping frames where the top tube is no longer horizontal, measuring frames changed. Unfortunately, the misconception persisted that frame sizes are universally measured the same way.

To address this, a more accurate approach involves considering “stack” and “reach” measurements, as introduced by Dan Empfield in 2003. These measurements provide a standardized and precise understanding of a bike’s dimensions, aiding cyclists in choosing the right size based on their individual preferences and body proportions.

The utility of the stack and reach values lies in their ability to provide valuable information for both customers and bike fitters:

For Customers: The Stack/Reach ratio offers an indication of the type of bike. Lower values (below 1.4) are often associated with “race” oriented bikes, providing a more aggressive and aerodynamic riding position. On the other hand, higher values (above 1.5) are associated with “endurance” oriented frames, offering a more relaxed and comfortable riding position.
For Bike Fitters: Stack and reach values are essential. These measurements help bike fitters prescribe a bike that suits the individual cyclist, considering their preferences, type of cycling, weight, and morphology. It aids in selecting the appropriate components for optimal performance and comfort.

The landscape of bike geometries has evolved significantly, with manufacturers offering a wide range from race-oriented to endurance-oriented frames. The extensive variety means that, except for extreme cases like very tall or very small cyclists, custom frames are generally not necessary. However, for cyclists seeking a highly tailored experience, custom frame builders can still provide exceptional craftsmanship, optimizing the properties of the materials used for a unique and optimized ride.

Ordering a bike without knowing your exact coordinates can be risky, especially with the increasing integration of cables in the cockpit. For road bikes with monobloc handlebars, it is advisable to know the handlebar coordinates HX and HY (handlebar reach and stack) to the center of the bottom bracket. This information becomes crucial for ensuring a proper fit and comfort, particularly with the evolving designs and features in modern bike components.

For triathlon and time trial bikes, relying solely on the indicated frame size provides limited information about the riding position it accommodates. Some may suggest choosing a size smaller than your road bike, but this is a risky generalization. Without a preliminary bike sizing, there’s a potential of purchasing a bike that doesn’t support your ideal riding position.

Prior to investing in such a bike, it’s crucial to determine the coordinates of the arm pads: Pad X (Arm pad reach) and Pad Y (Arm pad stack). The purpose of bike sizing is to ascertain these coordinates and utilize them to compile a list of suitable bikes – it’s essentially a ‘bike prescription.’ The relatively small cost associated with this approach pales in comparison to the safety and accuracy it ensures in making the right choice.