Frame stack and reach vs handlebar and hood coordinates
Frame geometry ends at the head tube; your controls do not. Learn which endpoint each number describes before comparing frames or passing a measured cockpit target to a tool.
Published 8 October 2026 · OpenBikeFit
Measurement field guide
Frame ≠ bar clamp ≠ hood.
F head tube: 390 / 560 · B clamp: 480 / 605 · H hood: 550 / 620
All X / Y values in mm from the same BB
Fictional points; not an approved build.
On this page
Record before interpreting
Use the free blank worksheet
Keep the physical reference, units and repeated readings together without creating a saved bike.
Open toolA frame size chart and a cockpit measurement can both be correct while describing different endpoints. Comparing them as if they were the same number creates a false mismatch or a false match. Start by naming the point, then decide which comparison the numbers can actually support.
This guide explains the coordinate chain from frame to bar clamp to controls. It does not recommend a frame size, spacer stack or stem. The fictional example is deliberately a set of measured point labels, not an approved build. Use real geometry and exact component information for any later modeling task.
Where frame stack and reach stop
In the conventional frame definition explained by Canyon, stack is the vertical component from the BB centre to the upper head-tube reference, and reach is the horizontal component to that reference. Check the manufacturer's geometry diagram for the exact point used. Neither value includes the full installed path to a handlebar or hood.
A size name such as medium does not define that coordinate. Two frames with the same stated stack can have different reach, head angles or permitted cockpit arrangements. Conversely, different frame coordinates can be associated with similar bar-clamp coordinates through different declared components. Similarity at one endpoint does not settle every downstream endpoint.
Define Bar X and Bar Y separately
For a BB-relative bar-clamp record, Bar X is the horizontal component forward of the BB centre and Bar Y is the vertical component above it. The physical endpoint is the handlebar-clamp centre, not the top of the bar, a lever tip or the end of a tape. The bike must be upright with level axles under the same measurement protocol used for comparison.
The headset, spacers, stem and clamp location form part of the coordinate chain between frame and bar. Model inputs need their own conventions, including the meaning of a stem angle. A catalogue's nominal angle and an actual installed centreline angle are not labels you can substitute without conversion and sufficient geometry. Read the tool's input definitions instead of guessing from a product name.
Follow one fictional coordinate chain
Consider three fictional points in millimetres: upper head-tube reference F is X 390, Y 560; bar-clamp centre B is X 480, Y 605; named hood point H is X 550, Y 620. They share one BB origin and the same axis directions. The diagram is schematic, not a scale drawing or an installation instruction.
From F to B, the coordinate differences are +90 mm X and +45 mm Y. From B to H, they are +70 mm X and +15 mm Y. A statement that frame reach is 390 mm does not therefore mean that the hood is 390 mm forward of the BB. A bar-clamp match at B does not prove that H will match on another cockpit.
These differences describe points, not a parts shopping list. They do not identify the stem, permitted spacer configuration, bar curve or control rotation that produced them. Even a geometric solution needs current component limits and physical verification. Do not reverse-engineer a compatible assembly solely from this illustration.
Why the hood is another endpoint
A hood reference depends on the selected feature on the control body. Record which point, which side and how it was located. Left and right control coordinates should not be merged just because one is easier to reach. Handlebar shape and control placement can change a named hood point while the bar-clamp centre stays the same.
Handlebar reach and drop describe aspects of the bar's shape under its manufacturer's convention. They are not automatically BB-relative hood coordinates. Rotation adds another reason to measure the installed point rather than adding catalogue dimensions without checking orientation. Keep bar and control identities beside the actual readings.
Reach and drop need endpoints too
A horizontal saddle-to-bar difference is not a direct diagonal tape length. A bar-top drop and a bar-centre drop also differ. For any saddle-to-cockpit measurement, name both endpoints and say whether the value is a signed horizontal component, vertical component or direct distance. A number called reach without that description can be impossible to compare later.
If the saddle endpoint or tilt convention changes, a saddle-relative reach/drop can change even when the BB-relative bar-clamp point has not moved. Keep those two coordinate families separate. BB-relative points are useful for component-to-component comparison, while a declared saddle-relative measure answers its own explicitly defined question.
Choose the tool that owns your task
The frame comparator works with a named BB-relative bar-clamp target. It does not treat a head-tube point as a hood target or certify a build because it is closest. The cockpit reach/drop calculator models signed changes from declared components. Before either task, record the installed baseline and understand what the model's output point represents.
If you only need to preserve a setup, use the blank worksheet or a local passport instead of constructing a hypothetical frame. If you need a workshop discussion, keep measured values, model outputs and still-missing checks visibly separate. The public fictional workshop example is a demonstration, not your bicycle or a compatibility certificate.
Compare like with like
A valid dimensional comparison needs matching origins, named endpoints, bike alignment, units and direction conventions. Keep the dates and individual readings. If one sheet ends at the head tube and the other at the hood, stop the subtraction and collect the missing point rather than manufacturing a conversion.
A coordinate match is only a coordinate match. It does not establish rider comfort, handling, safe component assembly or an ideal fit. Current physical measurements and exact manufacturer instructions remain necessary for any later mechanical work. This page helps you choose a meaningful input, not skip those responsibilities.
Practical questions
Frequently asked questions
Does frame reach tell me how far away the hoods are?
No. Frame reach ends at the upper head-tube reference. Stem, spacers, handlebar and control placement affect the path to a separately named hood point.
Can two frames have the same cockpit despite different stack and reach?
A named bar-clamp point can be geometrically similar through different declared components. That alone does not prove the same hood coordinates, compatible assembly or fit.
Should I enter frame stack as Bar Y?
No. Those fields refer to different endpoints. Measure or model the correct point under the tool's stated datum; do not relabel a frame-table value.