In cycling, Q Factor is the distance between the outer sides of the two crank arms, measured laterally.
Despite being an important element in bike fit that can have a significant effect on pedaling efficiency, comfort, injury prevention, and even handling, Q Factor is surprisingly poorly understood by most cyclists.
Having spent years working in bike shops and later as a professional bike fitter, I could probably count on one hand the number of times a cyclist asked me about Q Factor when discussing a new bike or crankset.
Having now worked as an ambassador for major component manufacturers such as Shimano and provided feedback on their prototype designs, I want to share my experience to help cyclists get clued up on Q Factor for themselves.
In this guide, I’ll be covering:
What Is Q Factor for Bikes?
Q Factor in bikes refers to the distance between the pedal attachment points on the crank arms. It essentially measures the width of the bike’s pedal stance, determining the rider’s stance width.
The term has a less scientific origin than you might think. Coined by bike designer Grant Petersen while at Bridgestone, the “Q” stands for “quack”, a light-hearted reference to the wide-stance waddle of a duck.
A narrower Q Factor brings the pedals closer together, while a wider Q Factor spaces them farther apart. This dimension significantly impacts a cyclist’s biomechanics, affecting hip, knee, and ankle alignment during pedaling.
The Q Factor will be different depending on the type of bike you are riding. For example, exercise bikes generally have a much wider Q factor than mountain or road bikes.
The Q Factor is determined by the width of the frame’s bottom bracket shell (rather than simply the bottom bracket width), how far the bottom bracket protrudes from the frame (if at all), and the length and angle of the crank arms.
Typical Q Factor Values for Different Bike Styles
| Type of Bike | Typical Q Factor |
|---|---|
| Track Bike | 140 mm |
| Road Bike | 150 mm |
| Gravel Bike | 150 mm |
| Mountain Bike | 170 mm |
| Fat Bike | 200 mm |
| Exercise Bike | 170 mm to 210 mm |
An example of people taking Q Factor to the extreme is Graeme Obree, who made a custom bike with a Q Factor of 40 mm for his Hour Record attempt. It even used washing machine bearings inside and was unlike any system we have in modern times.
How To Measure Q Factor for Bikes
Q Factor can be measured pretty easily, but it needs to be done in a particular way. The proper way to measure the Q Factor is from the outside of the crank at the pedal spindle vertically across the bottom bracket.
So imagine looking at a crank from the top, drawing a horizontal line alongside each pedal hole, and then measuring it in between through the bottom bracket. This will be your Q Factor.
As mentioned above, you will likely find it to be anywhere between 140 mm and 210 mm.
How Does Q Factor Affect Your Bike?
The width of the Q Factor can change how the bike rides. Here’s what to expect as someone who has experimented extensively with both wide and narrow Q Factors.
Effects of a Short Q Factor Bike
A short (narrow) Q factor on a bike brings the pedal attachment points closer together. This can have several effects on the bike and rider:
- Improved Pedal Stroke Efficiency: According to studies conducted by the University of Birmingham, a narrower stance can promote a more natural alignment of the rider’s legs, potentially reducing lateral knee movement and improving pedaling efficiency.
- Enhanced Aerodynamics: With the legs closer together, riders may have a reduced frontal area, leading to improved aerodynamics. This is why Obree pushed his Q Factor to such an extreme with his Hour Record bike.
- Increased Cornering Clearance: A shorter Q factor can provide better clearance during tight turns or maneuvers, reducing the risk of pedal strikes on the ground.
- Potential for Improved Comfort: Some riders find that a narrower Q factor feels more natural and comfortable, particularly those with narrower hips or a preference for a more compact riding position.
- Potential Mechanical Issues: When taken to the extreme, a very short Q Factor could introduce problems with the chainline by bringing the chainrings closer to the center of the bottom bracket shell. It could also cause your cycling shoes to rub on the chainstays.
Effects of a Long Q Factor Bike
- Increased Stability: A wider stance can provide greater stability, especially at higher speeds or when riding over rough terrain. This can be particularly beneficial for off-road or mountain biking where stability is crucial, which is why MTB Q Factors tend to be around 20 mm longer than road bikes.
- Reduced Risk of Knee Strain: For riders with wider hips or those who naturally have a wider stance, a longer Q factor can help prevent excessive knee strain by allowing for a more natural alignment of the legs during pedaling. Lance Armstrong, for example, suffered from tendonitis when experimenting with the 50 mm Q Factor used by rival Jan Ullrich’s iconic Walser time trial bike.
- Potential for Improved Power Output: Some riders may find that a longer Q factor allows for a more powerful pedal stroke, as it provides a wider base of support for the legs, potentially enabling better force transmission through the pedals.
Biometrics
When it comes to biometrics on Q Factors, many studies have shown some riders to gain performance from using either a wider or a narrower Q Factor. Many riders find narrower to be better, from my experience, but the difference has only been around 1% to 2%.
It comes down to the rider more than anything. Just as a single saddle doesn’t work for all riders, the same goes for Q Factor. The difference isn’t huge, though, unless you are a top-level elite going for a record.
If you have issues with knees or hips, you could fall into a rare category of someone who just doesn’t get along with standard Q Factors. For an expert opinion, it’s best to see a bike fitter about the correct Q Factor bike for you.
Can I Adjust The Q Factor on my Bike?
This can be done in many ways, but adjusting the cleat on your shoes is the easiest. Moving the cleat inwards toward the pedal pushes the shoe out further.
If that doesn’t give you enough adjustment, you can also experiment with longer pedal spindle lengths from companies such as Shimano and Speedplay.
Note that although you’ll be making your stance wider, neither of these options will technically be changing the Q Factor.
That could be achieved by adding spacers
Is Q Factor Important?
As a bike fitter and experienced cyclist, I get asked many questions about crank length, saddle height, and even handlebar angle. Q Factor very rarely comes up, and it’s really set for us by manufacturers more than anything else.
It’s clear in races like the Tour de France that pro riders are on industry standards too. Only the elite is looking for every marginal gain on events such as the hour record we see Q Factor get looked into.
As a general cyclist, I think it’s not something you should overthink unless you get hip or knee pain regularly and are already set up at the correct saddle height, crank length, and cleat position is the widest.
Then, you might want to consider contacting an expert bike fitter.
