Q Factor (Bicycles)
Encyclopedia
The Q Factor of a bicycle
is the distance between the pedal
attachment points on the crank arms
, when measured parallel to the bottom bracket
axle. It may also be referred to as the "tread" of the crankset. The term was coined by Grant Petersen
during his time at Bridgestone Bicycles.
Q Factor is a function of both the bottom bracket width (axle length) and the crank arms. Bottom brackets axles vary in length from 102mm to 127mm. Mountain bike cranks are typically about 20mm wider than road cranks.
A larger Q Factor (wider tread) will mean less cornering clearance for the same bottom bracket height and crank arm length. A smaller Q Factor (narrower tread) is desirable on faired recumbent bicycle
s because then the fairing can also be narrower, hence smaller and lighter. Sheldon Brown
claims that a narrower tread is ergonomically superior because it more closely matches the nearly-inline track of human footsteps.
Though it seems intuitive that a narrower tread is superior, it must be remembered that a walking person must put their foot more to the centerline of the body to balance. This is not the case when pedaling a bicycle, where the "steps" are so very close together and balance a non-issue.
Recent scientific research has emerged from The University of Birmingham
in the United Kingdom that shows narrower Q Factors are more efficient, likely due to improved application of force during the pedal stroke
Bicycle
A bicycle, also known as a bike, pushbike or cycle, is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist, or bicyclist....
is the distance between the pedal
Bicycle pedal
A bicycle pedal is the part of a bicycle that the rider pushes with their foot to propel the bicycle. It provides the connection between the cyclist's foot or shoe and the crank allowing the leg to turn the bottom bracket spindle and propel the bicycle's wheels...
attachment points on the crank arms
Crankset
The crankset or chainset , is the component of a bicycle drivetrain that converts the reciprocating motion of the rider's legs into rotational motion used to drive the chain, which in turn drives the rear wheel...
, when measured parallel to the bottom bracket
Bottom bracket
The bottom bracket on a bicycle connects the crankset to the bicycle and allows the crankset to rotate freely. It contains a spindle that the crankset attaches to, and the bearings that allow the spindle and cranks to rotate. The chainrings and pedals attach to the cranks...
axle. It may also be referred to as the "tread" of the crankset. The term was coined by Grant Petersen
Grant Petersen
Grant Petersen is a bicycle designer and the founder of Rivendell Bicycle Works. He was U.S. marketing director for Bridgestone Cycle , Inc...
during his time at Bridgestone Bicycles.
Q Factor is a function of both the bottom bracket width (axle length) and the crank arms. Bottom brackets axles vary in length from 102mm to 127mm. Mountain bike cranks are typically about 20mm wider than road cranks.
A larger Q Factor (wider tread) will mean less cornering clearance for the same bottom bracket height and crank arm length. A smaller Q Factor (narrower tread) is desirable on faired recumbent bicycle
Recumbent bicycle
A recumbent bicycle is a bicycle that places the rider in a laid-back reclining position. Most recumbent riders choose this type of design for ergonomic reasons; the rider's weight is distributed comfortably over a larger area, supported by back and buttocks...
s because then the fairing can also be narrower, hence smaller and lighter. Sheldon Brown
Sheldon Brown (bicycle mechanic)
Sheldon Brown was an American bicycle mechanic and technical authority on bicycles. He contributed to numerous print and online sources related to bicycling, bicycle mechanics and maintenance, including his own website — and received numerous awards for his contributions.-Biography:Brown...
claims that a narrower tread is ergonomically superior because it more closely matches the nearly-inline track of human footsteps.
Though it seems intuitive that a narrower tread is superior, it must be remembered that a walking person must put their foot more to the centerline of the body to balance. This is not the case when pedaling a bicycle, where the "steps" are so very close together and balance a non-issue.
Recent scientific research has emerged from The University of Birmingham
University of Birmingham
The University of Birmingham is a British Redbrick university located in the city of Birmingham, England. It received its royal charter in 1900 as a successor to Birmingham Medical School and Mason Science College . Birmingham was the first Redbrick university to gain a charter and thus...
in the United Kingdom that shows narrower Q Factors are more efficient, likely due to improved application of force during the pedal stroke