tech
Understanding Q Factor
Q factor is the overall width of an installed crankset, measured parallel to the bottom bracket shell from the outside of one pedal insertion point to the other. You can think of it like this: the larger the Q factor, the farther apart your feet will be.
Practical Implications
Q factor has long been a measurement of concern for crank manufacturers and cyclists alike. An overly-wide Q factor results in decreased pedal-ground clearance while the rider is turning. An overly-narrow Q factor will cause chainstay clearance issues at some point. Not all Q factors will be compatible with all frames.
Modern Developments
Generally speaking, Q factor is kept as narrow as possible without impacting frame clearance. Several developments have pushed Q factor farther from the centerline of the bicycle, primarily:
- The increased use of triple-chainring cranksets, which require moving the drive-side crank arm further out
- Wider chainstays on mountain and downhill frames for increased tire clearance
- The introduction of outboard bearings on standard threaded frames effectively increasing the width of the bottom bracket shell
- The growing number of "fat bikes" designed with much wider chainstays and a wider-than-standard bottom bracket shell in order to accomodate 4" or wider tires
Choice in Q Factor
Q factor is not usually advertised by crank manufacturers or QBP. However, some crankset models have recently been made available in multiple Q factor variations. For these cranksets, QBP will identify Q factor width in the item description.