Q Factor in Cycling: Pedal Stance Width Explained

The Q factor is how far apart your feet sit on the pedals. It gets little attention, yet it changes how your knee works on every pedal stroke. Here is what it is, what changes it, and what studies have actually measured.

What Is the Q Factor?

The Q factor is the horizontal distance between the outer faces of the two crank arms, the arms that connect the crank axle to the pedals. It sets how far apart your feet are throughout the pedal stroke, a bit like step width when you walk.

It depends mainly on the crankset: the width of the bottom bracket shell (the part of the frame where the crank axle turns), the room needed for the chainrings and the tyres, and the shape of the crank arms. That is why it varies more from one discipline to another than from one rider to another. Source: Disley, doctoral thesis, University of Birmingham, 2014.

Other parts also move your feet outward or inward:

the length of the pedal axles;
pedal spacers (small washers fitted between the pedal and the crank arm);
the side-to-side position of the cleats under your shoes.

Typical Values

Road bike: about 150 mm.
Mountain bike: about 180 mm.
Indoor bikes: from 147 mm to about 210 mm depending on the model.

No mass-produced bike goes below about 135 mm. Sources: Thorsen, Strohacker, Weinhandl and Zhang, Journal of Sport and Health Science, 2020; Wilbert et al., Bioengineering, 2024.

What Studies Show

A narrower stance, slightly better efficiency

In the lab, on an adjustable bike, trained cyclists pedalled with stance widths of 90, 120, 150 and 180 mm. At 90 and 120 mm, their efficiency (the share of the energy spent that becomes power on the pedals) was slightly better: about 1.5 to 2% more power at moderate effort. The muscles measured did not work any differently. Source: Disley and Li, Scandinavian Journal of Medicine and Science in Sports, 2014.

Note: 90 and 120 mm are lab settings. No production bike goes that low.

The stance width riders choose themselves

When trained cyclists are left to choose their own stance width, the average is around 142 mm, a little below the 150 mm road standard, with differences from one rider to another. Source: Disley, doctoral thesis, University of Birmingham, 2014.

A wider stance loads the inside of the knee more

When stance width goes from 150 to 276 mm, the load on the inner side of the knee increases: its peak rises by 47 to 56% depending on intensity. The knee's main effort, the one that pushes the pedal down, does not change. Source: Thorsen, Strohacker, Weinhandl and Zhang, Journal of Sport and Health Science, 2020.

In small steps of about 2 cm, the effect only shows clearly at the widest settings. Source: Wilbert et al., Bioengineering, 2024.

These measurements were taken in people without pain: they show a mechanism, not a treatment.

When to Think About It

The Q factor deserves a look if:

you have pain on the inside of the knee and ride with a wide stance (mountain bike, some indoor bikes);
your heels touch the crank arms;
you feel too wide, or too narrow, on the pedals.

Change one thing at a time (spacers, pedal axle or cleat position), in small steps, and see a professional if the pain persists.

What BikeFit AI Measures, and What It Doesn't

A BikeFit AI analysis is done from the side: it measures the angles of your knee, hip, ankle, torso, shoulder and elbow while you pedal. From the side, stance width can't be seen: BikeFit AI does not measure your Q factor, nor how your knee tracks when seen from the front.

If you change pedals, cleats or spacers, a new analysis lets you check that your side-view angles stay within the ranges for your discipline.

Frequently asked questions

Article by the BikeFit AI team, based on the studies cited.