Stack and reach: a useful way to compare bike frames
Stack and reach describe two coordinates of a frame: how high and how far forward its head tube sits relative to the bottom bracket. They are handy for comparing frame shapes, but they do not describe your complete riding position. Here is how to use them without asking two numbers to answer everything.
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What are stack and reach?
Reach is the horizontal distance from the center of the bottom bracket to the center of the top of the head tube. Stack is the vertical distance between those same reference points. Check each maker’s own definition and table units. Trek’s Slash geometry chart, for example, lists frame reach and frame stack in millimetres and defines each reference point.
Because the measurements share the bottom-bracket reference, they can make frame comparisons clearer than a size name alone. “Medium” is a label within a maker’s range; it is not a universal dimension. But stack and reach still leave out the stem, bars, headset cover, spacers, saddle position, and rider. Two frames with matching coordinates can end up with different hand positions.
For an overall introduction to charts and other measurements, see understanding bike geometry.
Compare two real bikes by size
Take a 2026 Trek Madone SL Gen 8 in size M and a 2026 Trek Domane AL Gen 4 in size 54. Trek’s published charts list the Madone M at 38.4 cm reach and 54.6 cm stack, and the Domane 54 at 37.4 cm reach and 57.5 cm stack. Converted to millimetres, those are 384/546 mm and 374/575 mm respectively.
For these two selected sizes, the Domane frame is 10 mm shorter in reach and 29 mm taller in stack. The original Trek charts use centimetres, so the converted values are multiplied by ten. These are frame coordinates from each bike’s bottom bracket, not a prediction that a rider’s hands will be 10 mm closer or 29 mm higher. The Madone uses Trek’s letter sizes and the Domane uses centimetre labels; this example does not recommend those sizes for the same rider.
Compare these bikes in Quiver to see the published dimensions side by side. For any comparison, confirm the exact year, frame generation, size, and configuration first. Stem, bars, headset cover, spacers, saddle position, and rider proportions all affect the assembled riding position.
What these numbers cannot decide
Stack and reach do not establish that a bike fits, that it will feel stable, or that its parts are compatible. They omit other frame geometry and the components that position your contact points. Trek’s owner fit instructions describe how handlebar and saddle adjustments affect reach to the bars and weight distribution. Fit questions depend on the rider and the assembled bike.
Use stack and reach to narrow a comparison, then inspect the rest of the chart: effective top tube, head angle, seat angle, chainstay, and wheelbase may be relevant to the question. Manufacturer tables may define or configure measurements differently, so read their notes. Quiver’s comparison tool can show available values by size; a missing entry remains missing rather than inferred.
If you already own one candidate, save its exact identity and size in your bike record. That gives you a grounded baseline when you compare another frame or record a change. Search the catalog for the published year and trim, then review which values actually have sources.
Make it about your bike
Find your bike in the catalog, then keep a record of what is on it in Quiver. Start with the details you know and add changes as you go.
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Manufacturer references and technical explanations used for this guide. Exact bike specifications still depend on model, year, size and market.