The "Q" factor pertains to the distance between your legs, especially when the subject is regarding bicycling. The part of the bicycle that most affects the Q factor is the bottom bracket's axle length. It was determined that the actual distance does not affect the overall mechanical performance of the cyclist. It could, however, affect those who have sensitive knees (those who have undergone surgery). Others might find discomfort to certain distances in the Q factor.

The Q factor, or quality factor, also pertains to oscillating systems, although it has a different definition in that context. It can be defined in many ways, one of which relates to the response of a driven resonant system as a function of drive frequency. The driven resonant system has some natural frequency fo, and the response curve has some characterstic width called the FWHM. the ratio of fo to the FWHM times 2pi gets a pretty good intuition for the Q factor. The Q factor also turns out to relate to the number of oscillations the damped resonant system can undergo - more quality means less oscillations.