Simply put, Q-Factor on a bicycle is the distance between the outer surfaces of the crank arms. This affects how far apart the pedals are, which in turn affects the biomechanics of pedaling and the handling of the bike. A bike fitter's rule of thumb for a good lateral fit is to have the hip, knee and foot all in line when pedaling, or stated another way, the center of the pedal/cleat is under the center of the hip. Given this, the body performs best with optimal muscle recruitment and the least likelihood of injury.
With the Voytek, we took a completely different approach to designing a fat tire capable bike. We started with a crankset that has Q-factor only 10mm wider than a "normal" mountain bike and roughly 20mm more narrow Q-factor than other fat tire capable bikes. This allowed us to achieve the optimal biomechanical fit on a carbon hardtail rocket ship that has tire clearance for some of the fattest tires available.
A summary of the Voytek and Q-Factor:
- The numbers: Narrow Q-factor crank arms -- the narrowest pedal stance of any production fat bike by a wide margin. Uses the 83mm bottom bracket standard (implemented as PF107) to provide an actual Q-factor as narrow as 183 mm. The result is the pedals are spaced only about 10 mm wider than a normal mountain bike whereas other fat bikes are typically 30-50 mm wider.
- The Biomechanics: Exclusive Otso narrow Q-factor fat tire capable design provides benefits in biomechanics. A narrow Q-factor reduces knee and hip strain while allowing proper/normal cycling muscle recruitment. Simply put, this means more efficient pedaling and painless/seamless transitions between fat biking and mountain biking.
- The Handling: Narrow Q-factor also improve bike handling making the Voytek handle like any other top of the line hardtail. Weight shifting, which is how riders generate much of their steering, causes a torque about the center of the bike based on where the rider’s foot pushes down. With a narrow Q-factor this torque is not only familiar but is also smaller with the foot being closer to the center of the bike. With a wide q-factor, this torque is much larger and creates an unwelcome and abrupt turning transition feel that all wide Q-factor fat bikes have.
- How we did it: Accomplishing this narrow Q-factor has not been done before on a production bike because it requires a custom offset chainring (not easy to do unless you make your own chainrings), a commitment to 1x drivetrains (Voytek is designed exclusively for 1x drivetrains), and some creative engineering with the chainstay design (we can be very creative).
Q Factor 101
Q-factor is a term used to describe a crankset’s width, measured in millimeters at the outside edges of the assembled crankarms.
This value typically ranges between 147 and 223, and is a function of crank spindle length, bottom bracket width/type, and chainstay specifications to ensure proper chain-line relative to tire dimensions and rear hub spacing.
The table below shows a list of typical Q-Factors based on bicycle type and discipline. For reference the Otso Voytek can be built with a 183mm Q-Factor.
Hopefully you can see that tire and wheel size impact these dimensions. Larger tires require wider chainstays; wider chainstays require increased hub spacing, bottom bracket width, and crankset q-factor.
Q-Factor is NOT Pedaling Base
Seeing as how there is no patent term to discribe the distance between a rider’s feet when pedaling, I am going to use the term “Pedaling Base” – a liberal adapation of “Walking Base” in Gait Analysis – to describe this feature.
For the sake of simplicity (and argument) let’s identify this location at the intersection of forefoot and pedal axle. A riders sum-pedaling base equals q-factor plus distance between each forefoot and crank at the pedal spindle.
Biomechanical Implications of Exceeding Appropriate Pedaling Base
Tibiofemoral (knee-joint) Biomechanics
Exceeding a cyclist’s pedaling base typically increases knee adduction moments (torque), and accompanying biomechanical anomalies that can cause acute pain or injury.
In simple terms, the knee is more likely to drive inboard towards the top-tube when an individual is riding outside his/her pedaling base. The impact of this feature on lower limb function can be injurious.
Muscle Recruitment Patterns – Training Effect
Altering a cyclist’s pedaling base impacts lower limb muscle & ligament tension and recruitment patterns established through training.
According to competitive cyclists’ reports, the period for adaptation is between 2 & 6-weeks. This means that 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. Put another way if you train on a typical fat bike for several months and then switch to a road or mountain bike you will lose some of that hard won leg fitness until you adapt to the muscle recruitment pattern of the narrower pedaling base.
Bicycle Handling Characteristics
A lateral shift in pedal force (relative to the frame’s central axis) requires additional counter steering to maintain a “neutral” position when cycling.
In addition, the resultant z-plane pedal-force vector is pushing the tires laterally, which is not ideal for traction in snowy conditions.
The illustration below illustrates how the resultant pedal-force vectors impact handling. Closer stance drives force in a vertical trajectory and wider stance drives a trajectory towards the bike's mid-line at the tires. This essentially causing rolling of the bike underneath rider in snowy conditions. Large tires tend to offset this altered trajectory by grabbing more contact area. Reducing the trajectory allows for similar stability when traction is limited or when running narrower tires.