This article explains in an easy-to-understand way what these terms mean - and why they are more important than frame size alone.
What does geometry mean in relation to bicycles?
The geometry describes the shape and dimensions of the bicycle frame. It significantly determines:
Previously, people often only considered the frame size (e.g., 54 cm or M). Today we know that two bicycles of the same size can ride completely differently – and this is precisely where stack and reach come into play.
Stack and Reach explained simply
Stack and reach are two key measurements that allow for an objective comparison of a bicycle's geometry.
Stack – the height
The stack describes the vertical height from the bottom bracket to the top of the head tube.
👉 Simply put: How high is the handlebar in relation to the pedals?
A high stack means:
A low stack means:
Reach – the length
The reach describes the horizontal distance from the bottom bracket to the center of the head tube.
👉 Simply put: How far forward do you have to stretch?
A long reach means:
A short reach means:
Why Stack & Reach are so important
Stack and reach are independent of marketing sizes like S, M or L. They allow a true comparison between different bikes and brands.
👉 Example: A size M racing bike from manufacturer A can feel completely different than a size M bike from manufacturer B - even though both are "the same size".
With Stack & Reach you can:
The ideal geometry depends heavily on the intended use:
🚴 Sporty & fast (e.g. racing bike )
🏕️ All-round / Gravel
Other important geometry values
Besides stack and reach, there are other dimensions that influence handling:
Head tube angle
seat tube angle
Chainstay length
short = agile
long = smooth running
wheelbase
longer = stable
shorter = agile
Stack-to-Reach Ratio: The Hidden Gem
A particularly helpful metric is the ratio of stack to reach.
👉 Formula: Stack ÷ Reach
Typical values:
< 1.45 → very athletic
1.45–1.55 → balanced
1.55 → comfort-oriented
This allows you to see at a glance which direction a bicycle is oriented.
How do you find the right geometry?
The perfect geometry depends on several factors:
Height & stride length
flexibility
Driving style
Area of application
Practical tips:
✔️ Analyze existing bicycle
➡️ Note and compare Stack & Reach
✔️ Take test drives
➡️ Feeling is crucial
✔️ Use small adjustments
➡️ Stem, spacers and saddle position can make a big difference
Conclusion: Geometry determines riding fun
Stack and reach are not abstract numbers – they determine whether a bicycle feels "right". Understanding these values allows you to:
👉 In short: It's not just the frame size that counts – but how the bicycle fits you.
