What is Q-Factor on a Bike
Q-Factor or Q-Faktor in German (Image Source: Knetsch and Holtkamp)
What is Q-Factor on a bicycle?
Q-Factor or crank width is the distance between the two pedal cranks and is a measure of stance width, which is similar to your walking step-width.
- QF Range
- 135mm on an aerodynamic Road Bicycle to 235mm for a Fat Tire Bike.
Grant petersen & Quack Factor
Grant Petersen, the founder of Rivendell Bicycle Works, bike author, and originator of the term Q-Factor says in his book, Just Ride: A Radically Practical Guide to Riding Your Bike:
"Q-Factor is the term I made up in 1990 to describe the distance between the outside of the left crank's pedal hole and the outside of the right crank's pedal hole."
and
"Crank makers talk about Q-Factor, but few know that the Q stands for "quack." Ducks waddle with their feet far apart relative to their leg length, and thus have high Q-Factors."
Q-Factor & Frame Clearance
Q-Factor is set by the crankarms, and is generally limited by bottom bracket width and tire clearance. Because of this, Q-Factor will differ between bicycling disciplines rather than between cyclists of different sizes.
Q-Factor size is largely determined by the frame clearance:
Rear tire-width clearance
Larger tires need more clearance and thus have larger Q-Factor (Fat Tire vs Road Bicycle tires)
Number of chainrings on your crankset
Mountain Bikes with multiple chainrings have larger Q-Factor (1X vs 3X drivetrain)
Single-speed bikes have lower QF compared to geared bicycles due to several factors including narrower chainstays
For example, larger tires require wider chainstays, which then further requires more hub space, then a wider bottom bracket, all of which increase the Q-Factor or distance between the pedals.
The image below, from Otso Cycles, shows the difference between bike components and their effect on Q-Factor.
Comparison of road bike and fat tire bike on QF (Image Source: Otso Cycles)
Image Source Journal of Sport and Health Science (2020)
Q-Angle, Q-Factor & Pedal Stance Width
Q-Factor, Q-Angle, and Pedal-Stance Width are NOT the same.
These 3 bicycle terms are not synonyms and should not be used interchangeably:
Q-Factor = horizontal width between pedals
Q-Angle (Quadriceps Angle) = measure of alignment between the femur and tibia
(Q—Factor does affect Q-Angle)
Pedal-Stance-Width = distance between the midpoint of the two feet
Q-Factor & Performance
Bicycles designers try to keep the Q-Factors as narrow as possible, regardless of bike type. Smaller Q-Factors are better for aerodynamics, handling, and are more natural for pedaling.
Awesome! Tell me more:)
Optimal Q-Factor & Walking
Q-Factor (QF) in cycling is similar to step-width in walking. The average walking step-width is between 70 to 120 mm and increases to 130 to 170 mm while climbing stairs. Even bicycles with very narrow QF are wider than the average walking step.
Since walking is human nature, it makes sense that bicycle engineers create bikes that put cyclists in their most natural position, which for Q-Factor means more narrow than wide as this more closely mimics our walking pattern or gait.
“A comparison between the stance phase of the gait cycle and the downstroke of the pedal cycle” (Image & Quote Source: Disley 2014)
Best QF for Bicycling
Before Q-Factor became a term, this same dimension was called “tread” over 100 years prior. However, not much scientific research has been conducted to determine the ideal Q-Factor, since the majority of studies focus their attention on seat height and aerodynamics.
What the available research says:
Narrow is better (up to a point as too narrow is possible)
Muscles work less the further the pedals are moved out (also up to a point….think about squatting at the gym)
Narrow QF improves riding efficiency (better power generation and more aerodynamic)
Hip-width to pedal-width (QF) is probably not that important
Every rider has a unique QF
Do you suffer from knee pain while cycling and have tried everything else?? A closer examination of your Q-Factor might be prudent
If your feet are positioned too narrow or too wide you may experience pain on the side of your knees or in your feet and will be more pronounced for those who ride clipless pedal systems.
Final Thought
The difference in performance between 90mm and 180mm is 5-watts. As Q-factor gets wider, especially for mountain bikes, your pedal efficiency suffers in order to increase downhill performance.
Jesse is the Director of Pedal Chile and lives in La Patagonia. Jesse has a Master of Science in Health and Human Performance and a Bachelor of Science in Kinesiology. Hobbies: Mountain biking, bicycle commuting, reading, snowboarding, researching, and sampling yummy craft beers.
Sources & references for “What is Q Factor On A Bike?”
Burt, Phil. Bike Fit : Optimise Your Bike Position for High Performance and Injury Avoidance. London, Bloomsbury, 2014.
Disley, B. X. (2014). Q Factor in cycling: kinematic and physiological effects [Doctoral dissertation, University of Birmingham]
Disley, Benedict Xavier, and Francois-Xavier Li. “Metabolic and Kinematic Effects of Self-Selected Q Factor during Bike Fit.” Research in Sports Medicine, vol. 22, no. 1, 2 Jan. 2014, pp. 12–22, 10.1080/15438627.2013.852093.
FitzGibbon, Sinead et al. “INTERVENTION AT THE FOOT-SHOE-PEDAL INTERFACE IN COMPETITIVE CYCLISTS.” International journal of sports physical therapy vol. 11,4 (2016): 637-50.
Jensen, RL, Watts, PB. Energy economy: effect of lateral pedal width variations relative to Q-angle in avid cyclists. In Proceedings of the XXVI Congress of the International Society of Biomechanics in Sports (Kwon, Y-H, Shim, J, Shim, JK, and Shin, I-S, editors) 2008;316-319
Knetsch, Tobias, and Max Holtkamp. “ATSB1805 Bike-Fitting I (Leistungssteigerung) [Institut Für Sportwissenschaft].” Wiki.ifs-Tud.de, 18 June 2018, wiki.ifs-tud.de/biomechanik/aktuelle_themen/projekte_ss18/atsb1805.
Otso Cycles. “Q-Factor and the Voytek.” Otso Cycles, otsocycles.com/pages/q-factor-and-the-voytek.
Petersen, Grant, and Retsu Takahashi. Just Ride: A Radically Practical Guide to Riding Your Bike. New York, Workman Pub, 2012.
Thorsen, Tanner Austin, "EFFECTS OF INCREASED Q-FACTOR ON KNEE BIOMECHANICS DURING CYCLING. " Master's Thesis, University of Tennessee, 2018.
Thorsen, Tanner, et al. “Increased Q-Factor Increases Frontal-Plane Knee Joint Loading in Stationary Cycling.” Journal of Sport and Health Science, vol. 9, no. 3, May 2020, pp. 258–264.