What is Q-Factor and why is it important in cycling?

What is Q-Factor?

Q-Factor, or the horizontal distance between the outside of one crank arm to the outside of the opposite crank arm, is a critical yet often overlooked aspect of bike fit. The term Q-Factor was coined by Grant Petersen in 1990, with the "Q" standing for "quack" - referencing the wide stance of a duck.

Important Distinction: It is not the Q-factor that we need to fit, but rather our stance width which affects how wide our feet and hips are on the pedals . While Q factor pertains to the width between the pedals, "stance" refers to the width between the feet while pedaling.

Why Q-Factor Matters: The Biomechanics

1. Joint Alignment & The Kinetic Chain

A correct Q-Factor helps align your hips, knees, and ankles, reducing the risk of injury and increasing pedaling efficiency. The aim is to achieve good hip, knee and foot alignment by aligning the foot to the knee.

The Real-World Problem: When Paul Swift (founder of BikeFit) raced track, coaches constantly yelled "bring your knees in!" At the top of the pedal stroke, the knee moved outward naturally to get closer to his ideal position for comfort. The knee then followed the foot faithfully down to discomfort town forcing it inward at the 6 o'clock position, placing significant torque on the knee when forced into an unnatural position - resulting in pain and potential injury (not to mention power loss).

2. Natural Stance Width vs. Fixed Position

Dr. Katrina Vogel reminds us that "you self-select your stance (width) when you walk, run stand or jump." Therefore, in sports when you are "locked-in," achieving the correct stance width is paramount to power delivery, efficiency, and injury prevention.

Q-Factor 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 Q-Factor are wider than the average walking step.

3. Efficiency & Power Output

Research at the University of Birmingham in the UK around 10 years ago by Dr Xavier Disley showed pedaling to be more efficient at narrower Q-factors than at wider ones. Link to full research findings here

A 2013 study with 24 subjects found significant increases in gross mechanical efficiency and 1.5-two per cent increases in power output as a result of using a Q-factor of 90mm versus 150mm. An abstract of this study can be found here.

4. Muscle Recruitment Patterns

If you switch from a bike with a narrow pedal base (like a typical road or mountain bike) to a bike with a very wide pedal base (like a typical fat bike) it will take 2 to 6 weeks to train your muscles to achieve optimal performance.

Common Q-Factor Issues & Symptoms

Too Narrow:

Too narrow a Q-Factor can lead to excessive supination, causing pressure along the outsides of the feet. Some riders will mistake this for their shoes being too narrow. Pain on the inside of (usually both) the knees, can often be due to insufficient stance width. This is often accompanied with knees that track outwards (away from the centerline of the bike) over the top of the pedal stroke.

Also, if the feet are too close together, it might result in hot spots or “saddle sores” and asymmetrical pressure on the saddle since your femurs are being forced to move more inward than their natural stance. This imbalance can cause discomfort and potential injuries over time.

Too Wide:

Pain on the outside of (usually both) the knees, can often be due to excessive stance width and you are simply pedaling “too wide” and not straight down.

Pedaling also outward while applying (downward) pressure to the pedals is less efficient and you lose/waste some power.

Typical Q-Factor Ranges by Discipline

Due to bottom bracket size, minimum chainline guidelines and chainstay length, there is an acceptable range for Q-factor, which is typically between 150mm and 170mm. Road bikes tend to have a narrower Q-factor (145-150mm), while mountain bikes tend to have a greater Q-factor (168-175mm). This is due to increased tire width, which forces the cranks out further from the midline of the bike to maintain clearance. At the extreme end, many fat bikes have a Q-factor of 200mm or more.

• SRAM’s current AXS Road cranksets have a Q-Factor of 145mm, with the WIDE (Gravel) version being 150mm

• SRAM’s Eagle AXS Transmission (MTB) cranks are stock 174mm in Q-Factor.

• Shimano Road cranksets have a Q-Factor of 148mm

• Campagnolo has a Q-Factor of 145.5mm for their road cranksets

• Fat Bikes have very wide Q-Factors due to tire clearance needs and often exceed 200-230mm

The "One Size Fits Most" Problem

It's difficult to believe that the majority of every asymmetrical human male and female size 4'8″ to 7'2″ would be accommodated by a 252mm (about 10 inches) stance width (252mm was obtained by using an average 53mm pedal spindle width on each side and a 146mm q factor). Cycling is like the "one size fits most" of clothing. We are not sure of who fits the "most" category but in our experience, "most" is more like “some”. And for example, a 46cm sized-bike has the very same crankset and Q-factor than the very same bike/model in size 61cm.

Individual Variation

Your optimum Q-factor is highly dependent on your anatomy, in particular the width of your pelvis. Taller people's natural stance width is typically wider than shorter people's, so they may need to adjust their Q-factor to reflect this.

Taller or broader individuals may require a wider stance to accommodate their body structure, while smaller, leaner cyclists might feel more comfortable with a narrower stance. Moreover, people with tight hips or restrictions due to sedentary lifestyles often benefit from a wider stance.

How We Can adjust Stance Width in Bike Fitting

Since Q-factor is fixed by the crankset, here are ways to adjust stance width:

1. Cleat Position

Moving the cleat towards the outside of the foot reduces the stance width, while moving it towards the inside increases the stance. Shimano SPD-SL road cleats let 6mm of lateral mobility per cleat Rothe-enterprises.

2. Pedal Spindle Washers

Adding spacer washers to the pedal spindles will increase your Q-factor by .75mm to three mm, depending on the width of the actual washer. Be careful though; this lowers the crankarm's pedal thread count, which can cause stripping—a possibly expensive error. Adding more than 2-3mm in washers to normal pedals is NOT recommended.

3. Pedal Axle Length

Some pedal systems offer pedals with varying axle lengths (Speedplay and Shimano). Choosing the right axle length helps in achieving the desired stance width.

4. Different Pedal Systems

Different pedal systems have varying Q-factors (the distance from crank face to pedal center), typically ranging 12-18mm.

5. Crankset Change (Last Resort)

Changing the entire crankset is expensive but may be necessary for riders with extreme anatomical needs.

Assessment During Bike Fitting

Signs indicating a stance width issue include: inverted foot presentation on the pedals (tipped up to inside), a report of increased pressure to the outside of the feet, a report of medial knee pain – may indicate a need for a narrower stance width, a report of lateral knee pain – may indicate a need for a wider stance width. Generally, we like to see multiple signs and symptoms which provide a weight of evidence to make a change to the stance width, rather than rely on a single factor.

Key Takeaway

Part of any bike fit is often to determine your natural stance width off the bike and adjust your fit on the bike to reflect this. The challenge is that stance width is an aspect of bike fitting that is under-represented in the research and is deserving of considerably more investigation, making it both an art and a science that requires careful assessment of multiple factors including anatomy, flexibility, injury history, and riding style of the rider. We fit your bike to your body and not your body to your bike!

Contact us to schedule your personal bike fit with us today!