We answer the question of what Q-factor is to unravel a frequently discussed measure of a bike's geometry
(Image credit: Josh Croxton)
Q-factor is the distance between the outside of one crank arm and the other, measured not diagonally, but laterally, through the midline of the bottom bracket.
Picture your crankset from above. You see the left crank arm at the back of its pedal stroke, parallel to the ground, and the right crank arm at the front of its pedal stroke, also parallel to the ground. The two-dimensional, lateral distance between the outside of the left crank arm and the outside of the right crank arm is the Q-factor.
Some refer to Q-factor as ‘stance width’, which makes more sense when you think about it. But it is important to note that your actual stance width is the measurement of the distance between your feet when on the pedals, and this can be altered without changing your Q-factor.
When you think about your natural stance off the bike, there is a certain width that is most comfortable for you. Whether it is walking, standing, jogging, or sprinting, there is a natural stance width that your feet fall into. Go wider or narrower, and it just feels wrong. Worse, your hips and knees will hurt, you will struggle to balance, and you could even develop an injury if you don’t correct the imbalance.
Stance width in cycling is similar, and there is an ideal, preferred stance width for everyone when cycling. Whereas Q-factor is dependent on your bike and its components.
The limits of Q-factor
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There is a limited range for Q-factor determined by both biomechanics and manufacturers.
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 (150mm), while mountain bikes tend to have a greater Q-factor (170mm). This is due to increased tyre 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. This brings your legs and feet much further apart, and some riders have likened riding a fat bike to straddling a horse – all because of the bike’s massive Q-factor.
Cyclists don’t need to worry too much about increasing their Q-factor on its own, because the main reason for wanting to do this is to increase stance width, which can be done by moving your cleats or getting a longer pedal spindle.
Performance benefits
Much like a bike fit, there are no inch-by-inch guidelines based on your height and weight. Each rider has different biological proportions, different preferences, and a different injury history that could affect their bike fit and thus, there are protocols in place that will set you up with your unique fit. However, 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.
What’s most important is to find a stance width that is comfortable and powerful. If you feel comfortable riding a few hours in the saddle, without any serious aches and pains, there isn’t any biomechanical reason why you’d want to change your stance width or Q-factor.
As stated above, there are industry standards for Q-factor that most people are completely comfortable with. Many riders need small adjustments to achieve the perfect fit, but this can often be accomplished with a slight tweaking of the pedals or cleats, rather than changing components to alter your Q-factor.
The phrase ‘narrow is aero,’ is not always true, and could even set you up for injury if you’re not careful. Decreasing your Q-factor, or bringing your crank arms closer together, may make you more aerodynamic, but it won’t necessarily make you faster. You may lose a significant amount of power, or stop recruiting your glutes in such a narrow position. By pushing it too far, you could create muscular imbalances that lead to chronic injury.
You can also change your pedal or cleat positions individually – left versus right sides – whereas you can only change Q-factor at once. This bilateral adjustment is especially helpful for someone with unique physiology or an injury history that has resulted in one leg being significantly different from the other in length or strength.
How Q-factor affects your pedalling
There is a lot of debate in cycling regarding the extent to which Q-factor alters or affects your pedalling. Many argue that pedals, cleats, and pedal spindle length combined have a greater effect on your pedalling than Q-factor alone. Add in adjustments to the mounts on your shoes, and you could have a completely different pedalling style without ever altering your Q-factor.
Your saddle can significantly affect your pedalling as well. Your hip angle, rotation, and width can change with a new saddle, and will have a large impact on your pedalling style and ideal stance width.
It is truly unknown the extent to which Q-factor affects your pedalling, but right now, we can confidently say that there are many other alterations you can make to your fit and stance width that will have a greater impact on your pedalling than Q-factor alone.
Conclusion
In many cases, it is both tedious and complicated to alter your Q-factor. Whether it’s a new bottom bracket, a new crankset, or a whole new bike, the price is steep. So if your goal is to alter your pedal stroke, or change your stance width, you can accomplish this by changing your pedals, cleat position, or pedal spindle length.
There’s hardly any science to back up the case for narrower Q-factors – 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 – but those studies are few and far between. It’s a theory that, when applied to the real world, has the potential to do a lot more harm than good. Until the studies start flooding in, there isn’t much evidence that Q-factor has a major impact on your pedalling and power output.
Before changing your Q-factor, first try altering your cleats, pedals, pedal spindle, or cleat alignment. You can achieve an extremely wide range of fits by altering these factors, and they can all be adjusted in just a few minutes each.
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Zach is a freelance writer, the head of ZNehr Coaching, and an elite-level rider in road, track, and e-racing. He writes about everything cycling-related, from buyer's guides to product reviews and feature articles to power analyses. After earning a Bachelor’s Degree in Exercise Science at Marian University-Indianapolis, Zach discovered a passion for writing that soon turned into a full-fledged career. In between articles, Zach spends his time working with endurance athletes of all abilities and ages at ZNehr Coaching. After entering the sport at age 17, Zach went on to have a wonderful road racing career that included winning the 2017 Collegiate National Time Trial Championships and a 9th place finish at the 2019 US Pro National Time Trial Championships. Nowadays, Zach spends most of his ride time indoors with NeXT eSport.
