Definition
Q-factor (also called stance width) is the horizontal distance between the outer faces of your pedals when both cranks are parallel to the ground. Measured in millimetres, Q-factor is set by the crankset, pedal spindle offset, and sometimes the bottom bracket or spacers. It’s a basic geometry number that feeds directly into how your hips, knees and ankles align under load.
Why It Matters
Q-factor influences comfort, injury risk, and marginal power delivery. A too-narrow or too-wide stance can change knee tracking, shift how your hips sit over the pedals, and force compensations that cost watts or cause pain over long efforts. It also plays into shoe clearance and chainline decisions on multi-chainring setups.
Quick links to parts that change Q-factor.
Cranksets & Chainrings — primary source of Q-factor differences between road and MTB cranks
Pedals — spindle offsets and axle width influence stance width
Bottom Brackets — spacers and shell width can alter effective Q-factor
Road Bike Pedals — lower stack and narrower spindles reduce overall Q
Cycling Shoes — sole width and cleat placement affect perceived stance
How It Works
Think of Q-factor as the sum of three horizontal components: crank arm width (where the pedal threads into the arm), pedal spindle offset, and any additional shift from bottom bracket and spacers. Visually, if you drew vertical lines down from each pedal spindle to the ground, Q-factor is the outside-to-outside distance.
A simple diagram you can imagine: two parallel crank arms, pedal spindles at the outer ends, and a measured gap between the spindle outer faces. Change any of those parts and the gap changes.
Crank design: road cranksets concentrate material closer to the chainrings, giving narrower Qs. MTB cranks push the chainring and arm outboard for chain clearance, increasing Q.
Pedals: platform pedals and some pedal spindles have offsets of a few millimetres. An MTB pedal with a wider axle and platform can effectively increase stance width.
Bottom bracket & spacers: threadless versus press-fit shells, or using spacers, will shift the chainline and can require cranks with different arm offsets, subtly altering Q.
Practical note: perceived Q is affected by shoe sole width and cleat placement. Two riders on identical cranks can feel different stance widths if one uses stiffer, wider soled MTB shoes vs a narrow road shoe.
> Pro tip: If you’re chasing a narrower pedal stance, start with road-style cranks and low-offset road pedals before swapping shoes or changing cleat positions.
Key Specs/Thresholds
Typical road Q-factor: ~145–155 mm. Many modern road cranksets cluster around 145–150 mm.
Gravel/adventure: ~150–165 mm depending on chainline and frame clearance.
Mountain bike Q-factor: ~160–175 mm; older MTB cranks can be even wider.
Track/TT cranks: often on the narrower end of road range (around 145–150 mm) for aerodynamics and single-ring chainlines.
Pedal spindle offsets: vary by brand; expect ±2–6 mm differences between models. Platform pedal axle width adds to perceived stance.
Cleat fore/aft adjustment: moving cleats laterally or fore/aft can change perceived knee tracking without changing measured Q.
Common Misconceptions
Q-factor is the same as chainline. Chainline is the lateral position of the chain relative to the frame; it correlates with Q, but they’re not identical.
Narrower Q always means faster. Not necessarily — if narrowing forces hip rotation or knee valgus, you lose efficiency and risk injury.
Shoes don’t affect Q. They do: sole width and cleat placement change where your foot sits relative to the pedal spindle.
You must match pro Q-factors. Pros have specific setups for power and clearance; copy their numbers only if your hip anatomy and riding style match.
When to Choose/Use
If you have recurring lateral knee pain or IT band issues, check Q-factor: if your knees track inward or outward under load, consult a fitter before swapping equipment.
If you ride mixed disciplines (road to gravel to MTB) and notice discomfort, keep discipline-specific cranksets/pedals rather than forcing one setup across all bikes.
If you want marginal gains on the road (smoother pedalling, small power gains), moving from a wide gravel crank to a road crank can narrow Q by ~5–15 mm and may help.
If frame clearance or a wide tyre/wheel combo limits chainring placement, accept a slightly wider Q as a trade-off for tyre clearance.
Sources
Park Tool (2021) — practical measurement and crank basics.
BikeFit (2019) — fitting principles linking Q-factor to knee tracking.
Shimano Tech Docs (2020) — crank and pedal spec sheets showing spindle offsets.
Journal of Biomechanics / PubMed (2014) — peer-reviewed studies on stance width and knee biomechanics.
Related Categories
Key Takeaways
Q-factor is the outside-to-outside width between pedals, measured in mm.
It affects knee alignment, comfort, and marginal power — not just aesthetics.
Crankset, pedal spindle, and bottom bracket combine to set Q-factor.
If you have persistent knee issues or discipline changes, consult a fitter before swapping parts.
FAQs
Will changing cranks fix my knee pain?
Possibly. Q-factor can cause lateral knee issues if it forces poor tracking. A bike fitter should evaluate cleat position, saddle height, and hip rotation first. If stance-width mismatch is the likely culprit, swapping to a crank with a different Q can be part of the solution.
How do I measure Q-factor on my bike?
Put both cranks horizontal and measure the outside-to-outside distance across the pedal spindles or platform faces with calipers or a tape. Record the number in millimetres. For consistency, measure from the outermost faces of the pedal axles.
Related Blogs
How to Dial Cleat Position | Competitive Cyclist
Cleat to Pedal Cross-Compatibility Explained | Competitive Cyclist
Chainline on a Bike and How It Affects Wear & Shifting | Competitive Cyclist
Crankset and Chainring Compatibility Explained | Competitive Cyclist