The Height Fallacy
Most bike sizing charts use rider height as the primary input. Stand here, you are a large. Stand there, you are a medium. It is a system that works just well enough to persist, and just poorly enough to misfit a significant percentage of riders.
The problem is that height tells you almost nothing about the cockpit. Two riders who are both 183 cm can have inseams that differ by 8 cm, torsos that differ by 10 cm, and arms that differ by 6 cm. Put them on the same large frame and one will feel cramped while the other feels stretched.
Reach Is the Dimension That Matters
Reach is the horizontal distance from the bottom bracket to the top of the head tube. It is the measurement that defines how much room you have between your feet and your hands, which is the single most important factor in how a bike handles while standing on the pedals.
When you are descending, you are not seated. Your weight is distributed between the pedals and the bars. Reach determines whether that distribution is balanced or compromised. Too little reach and you are crowded, fighting to get your weight back. Too much and you are stretched, unable to shift forward for steep climbs.
The S-Volve Approach
Our S-Volve sizing system uses reach as the primary sizing metric, with rider height as a secondary check rather than the primary filter. The process is straightforward:
- Measure your preferred reach based on your riding style and proportions.
- Select the frame that delivers that reach within its geometry range.
- Fine-tune with the Reach Adjust (RA) system, which allows cockpit length adjustment without changing the frame.
This is why the Paratu CP and Iuhu CP are offered with detailed reach data rather than a simple height chart. The geometry table tells you exactly what you are getting, and the RA system lets you dial it in after the fact.
What This Means for You
If you have ever been between sizes on a traditional chart, or felt that a bike that should have fit you did not, reach is likely the reason. A medium frame from one brand can have a shorter reach than a small from another. The label is not the geometry.
The recommendation is simple: ignore the size label. Find your reach, find the frame that matches it, and adjust from there. Your riding will be more balanced, more controlled, and more comfortable for it.
For the full geometry tables and Reach Adjust details, see the Geometry page.