Q-factor vs pedal stance width: name the endpoints before comparing millimetres
Crank Q-factor, a one-sided pedal offset and the distance between shoes are different widths. Learn the conventions and why a cleat's lateral move is opposite to the shoe's move.
Published 8 October 2026 · OpenBikeFit
Pedal interface field guide · schematic
Name both sides before adding.
Fictional Q 150 mm + left 53 mm + right 53 mm = 256 mm
Pedal-centre span is not automatically anatomical foot span.
Schematic, not to scale, an approved assembly or a stance target.
On this page
- 01Crank Q-factor starts at the crank arms
- 02A pedal catalogue may use Q-factor differently
- 03Add the two sides only when their references match
- 04Pedal-centre span is not anatomical foot span
- 05A cleat move reverses the shoe move
- 06Preserve limits instead of inventing an axle solution
- 07Record a baseline before opening a trial
Identify before adjusting
Inspect one marked cleat trial
Use the existing free workflow and its own gates. Reading a guide or opening a tool does not approve hardware or create a trial.
Open toolA 53 mm pedal specification and a 150 mm crank specification can both be labelled Q-factor without contradicting each other. They may describe different pairs of endpoints. A third number, the distance between shoes or feet, includes more of the assembly. Comparing those values without naming their references is like comparing frame reach with hood reach: the unit is the same, but the geometry is not.
This guide separates crank attachment width, one-sided pedal offset, pedal-centre span and a named shoe or foot span. It provides a fictional addition example and a recording method, not a target based on hip width or an instruction to install longer axles, washers or extenders. Physical compatibility and rider suitability remain separate from dimensional arithmetic.
Crank Q-factor starts at the crank arms
SRAM defines crank Q-factor as the distance between the pedal attachment points on the crank arms. Preserve that definition when reading a crank specification. It is not the distance between the two pedal centres after pedals are installed, and it is not the length of either crank arm from bottom bracket to pedal axle.
A crank-length change concerns the pedal's circular path around the bottom bracket. A crank-width change concerns lateral separation. One can change while the other stays constant, or a component replacement can change both. Record the model and both quantities rather than assuming a familiar crank length preserves every aspect of the pedal interface.
A pedal catalogue may use Q-factor differently
LOOK's 53/56 mm support page uses Q-factor for the distance from a crank arm to the pedal centre. TIME calls that one-sided dimension pedal center or spindle length and treats crank Q-factor separately. Those labels demonstrate why the drawing or definition must travel with the number. Do not decide that a smaller printed value is a narrower whole-bike stance until you know the endpoints.
Record the mounting face at the crank and the specified pedal-centre reference on each side. The physical assembly may not match an informal measurement to the end of the spindle or the edge of the platform. A catalogue dimension should be identified as declared, and an installed measurement as measured; neither should be silently renamed to make two records appear comparable.
Add the two sides only when their references match
For a fictional symmetric assembly, let crank attachment width Q be 150 mm and each mounting-face-to-pedal-centre offset be 53 mm. Pedal-centre span is 150 + 53 + 53 = 256 mm. If both offsets become 56 mm under the same definitions, that span is 262 mm, a total change of 6 mm. A one-side change of 3 mm is not automatically a whole-span change of 3 mm.
More generally, use Q plus the left offset plus the right offset; doubling one side assumes symmetry. The example is exact addition under declared endpoints, not a real approved parts combination or a width recommendation. It does not account for shoe placement relative to the pedal centre, and it cannot validate thread engagement, routing, heel clearance or the permissibility of an added spacer.
Pedal-centre span is not anatomical foot span
A shoe can be positioned laterally relative to the cleat retained in the pedal. Its centreline, inside sole edge and a particular anatomical foot point are different references. That means the same pedal-centre span can coexist with different recorded shoe spans. If the goal is an installed shoe measurement, name the point on each shoe and the condition in which it was measured.
Avoid a universal instruction such as match stance to hip width. This guide has no validated body-to-width formula and does not infer a preferred position from how a knee appears in one video plane. Left and right records can differ without that observation proving a diagnosis or requiring symmetry. Keep the observation and the interpretation separate.
A cleat move reverses the shoe move
Imagine the pedal and its retained cleat fixed in space. If the cleat is moved toward the inside of the shoe before re-fastening, the engaged shoe sits farther outward relative to that same cleat. Conversely, moving the cleat toward the outside of the shoe brings the shoe inward. This is relative-position geometry, not a command to move a particular rider's foot.
OpenBikeFit's lateral recording convention measures from the inside edge of the shoe sole to the cleat reference mark. A larger coordinate is closer to the shoe's outside edge. Read the direction label as a cleat movement under that sole reference, not as an automatic wider-foot instruction. Name the chosen side because a page viewed from the sole can otherwise make inward and outward ambiguous.
Preserve limits instead of inventing an axle solution
Available shoe slots, correct support against the sole, fastener engagement, pedal design and clearance constrain a real change. A numerical difference between two catalogue widths does not authorize an axle transplant, stacked washers or an extender. Use the current instructions and accepted parts for the exact models; if those are missing, the assembly remains unresolved.
A cleared coordinate in an application is not a mechanic's inspection. Do not deliberately ride with uncertain retention, insecure hardware or unpredictable release to test whether a width feels better. The useful next step can be a question to the manufacturer or mechanic, supported by the named dimensions and photographs rather than a guessed replacement part.
Record a baseline before opening a trial
Write the crank identifier, its defined attachment width, the two pedal models and offsets, the two shoe references and the cleat marks. Mark which figures are catalogue declarations and which were physically measured. If one endpoint cannot be identified, leave its value unknown. You can document this on paper without a saved bike or a new camera session.
The existing cleat assistant concerns one explicitly chosen side and axis, with its own limited amount, original-position confirmation and re-check gates. It does not calculate a body-based stance or approve pedal-spacing hardware. The crank calculator concerns crank length and its coupled model, not a hidden width mode. Choose a tool by the quantity you can name instead of transferring a number into the nearest input.
Practical questions
Frequently asked questions
Why do crank and pedal Q-factor numbers look so different?
They can use different endpoints. Crank Q-factor can mean distance between crank pedal-attachment points, while a pedal maker can use it for one crank-to-pedal-centre offset. Read the definition or drawing.
Does adding 3 mm on each pedal change total span by 3 mm?
Under the same symmetric references it changes the pedal-centre span by 6 mm. That is dimensional addition, not approval to add washers or use an unverified axle or extender.
Does moving a cleat inward move the shoe inward?
With the retained cleat and pedal fixed, moving the cleat inward relative to the shoe places the engaged shoe farther outward. Always state which object, side and view the direction describes.
Can a hip-width measurement give my correct pedal stance?
This guide provides no body-to-stance prescription. Define and record the installed endpoints, retain component limits, and keep individual suitability separate from catalogue arithmetic.