The crank length madness: everything you need to know about shorter cranks
Introduction: A new trend in crank lengths
In recent months, a noticeable trend has emerged in the cycling world: the Crank Length Madness. More and more professional cyclists, regardless of their height, are switching to shorter cranks, such as 165 mm. Even taller riders are making this choice. But is this decision rooted in scientific evidence or simply based on the idea that “if Pogi does it, so should we”?
At Bikefit Van Staeyen, we’ve spent the past years studying the effects of shorter cranks on biomechanics, joint stress, and power output. While there are clear advantages, shorter cranks are not the perfect solution for everyone.
A closer look at the numbers: why crank length matters
Let’s start with the basics: crank length is the distance between the center of the bottom bracket and the pedal axle. While it might seem like a small detail, this measurement has a massive impact on your biomechanics, efficiency, and overall performance.
1. Hip Angle and Power Generation
The Data: Shorter cranks increase the hip angle at the top of the pedal stroke. For every 10 mm reduction in crank length, the hip angle opens by approximately 4-6 degrees, depending on saddle height and torso position.
What This Means: A more open hip angle reduces compression forces on the hip joint (acetabulofemoral joint) and relieves strain on the iliopsoas muscle.
Practical Example: Riders with a hip flexion angle of 50 degrees using 175 mm cranks can increase this to 54–56 degrees with 165 mm cranks. This change allows for a smoother and less restricted pedal stroke.
Joint stress: the key to longevity
Knee Flexion and Patellar Load
The Data: A study in the Journal of Biomechanics (2021) showed that reducing crank length decreases knee flexion by up to 15 degrees at the top of the pedal stroke.
175 mm cranks: Knee flexion ~120 degrees.
165 mm cranks: Knee flexion ~105–110 degrees.
Impact: Decreased flexion reduces patellar stress by up to 18%, making shorter cranks ideal for riders with knee pain or overuse injuries.
Lower Back Strain
Shorter cranks ease hip flexion, which in turn reduces lumbar spine compression forces. This can help prevent lower back pain, especially during long rides or climbs.
Thermal Imaging Insight: In rides lasting over an hour, riders using shorter cranks showed 12–15% less heat buildup in the lumbar region, a clear indicator of reduced stress.
The myth of power loss
A common misconception is that shorter cranks lead to power loss due to reduced leverage. Let’s break this down:
1. The leverage debate
Torque and Crank Length: It’s true that longer cranks provide more leverage, but the effect is minimal. For example:
Switching from 175 mm to 165 mm reduces leverage by only 5.7%, which translates to about 1-2% less torque.
Real-World Impact: In a simulated time trial test, riders maintained an average power of:
175 mm cranks: 310 W.
165 mm cranks: 308 W.
2. Cadence Advantage
Shorter cranks allow for higher cadence due to the smaller pedal circle. Field tests showed that riders using 165 mm cranks increased their cadence by 3–7 rpm, compensating for any loss in torque.
Efficiency Data: At higher cadences, oxygen consumption decreased by 2-4%, meaning riders could sustain efforts longer.
EMG and thermal imaging: what the body reveals
Muscle Activation (EMG)
We analyzed muscle activity across crank lengths using EMG sensors on key muscle groups:
Quadriceps: Consistent activation across all crank lengths.
Hamstrings: Slightly lower peak activation with shorter cranks, indicating reduced strain.
Glutes: More balanced activation with shorter cranks, suggesting improved stability.
Thermal Imaging
Using thermal cameras, we measured heat buildup (a marker of strain) in key areas:
Knees: Riders using shorter cranks showed less heat buildup, reducing injury risk.
Hips and Lower Back: Reduced heat, correlating with better hip flexion and spinal alignment.
Climbing vs. sprinting: where shorter cranks shine
Climbing
Shorter cranks allow for a more forward saddle position, aligning the rider’s weight over the pedals for better climbing efficiency.
Simulated Gradient Test: At a 10% gradient, riders with shorter cranks maintained a 3-5 bpm lower heart rate, a sign of improved efficiency.
Sprinting
While longer cranks provide slightly more leverage, shorter cranks allow for faster accelerations due to their smaller pedal arc.
Track Data: Riders using 165 mm cranks reached peak cadences 6-8 rpm higher, crucial for track cycling and criterium sprints.
Crank lengths for time trial bikes and triathletes: a unique case
When it comes to time trial bikes and triathletes, the case for shorter cranks becomes even more compelling. The aero position adopted in time trials places unique demands on the body, particularly on the hip angle, oxygen delivery, and power output. However, even in this scenario, shorter cranks are not always the perfect solution, they must be customized to the individual athlete based on detailed biomechanical and vascular assessments.
Why shorter cranks make sense for time trials and triathlons
Aerodynamics and Hip Angle
In a time trial position, the rider’s torso is significantly more horizontal, compressing the hip angle. With traditional crank lengths (e.g., 170–175 mm), the hip angle often becomes too acute at the top of the pedal stroke, limiting power output and causing discomfort.
Data Insight: Moving from a 175 mm to a 165 mm crank opens the hip angle by 5–8 degrees, depending on the individual’s flexibility and saddle position.
Impact: This allows for a more sustainable aero position, reducing fatigue and strain on the hip flexors, especially during longer efforts typical of triathlons.
Muscle Engagement and Stability
Shorter cranks lead to more balanced muscle engagement, particularly in the glutes and hamstrings, which are critical for maintaining power in the aero position.
EMG Data: Time trialists using shorter cranks showed a reduction in quadriceps dominance and improved activation of the posterior chain, resulting in better overall efficiency.
The role of hemoglobin and oxygen delivery
At Bikefit Van Staeyen, we take a unique approach by incorporating Near-Infrared Spectroscopy (NIRS) to measure hemoglobin levels and assess tissue oxygenation during the bikefit process. This technology allows us to see how crank length affects blood flow and muscle perfusion in real-time.
NIRS Insights for Time Trialists
Blood Flow in the Aero Position
The aero position naturally compresses the femoral artery and reduces blood flow to the quadriceps and hamstrings.
With shorter cranks, the reduction in hip flexion improves vascular function, ensuring better oxygen delivery to the working muscles.
Data Example: A triathlete using 175 mm cranks experienced a 12% drop in hemoglobin saturation during sustained aero efforts, compared to only a 6% drop with 165 mm cranks.
Balancing Oxygen Supply
NIRS data also revealed that shorter cranks can help distribute oxygen demand more evenly between muscle groups, reducing the likelihood of early fatigue or cramping in the quads during long-distance triathlons.
When shorter cranks aren’t better
Even for time trialists and triathletes, shorter cranks aren’t always the best choice. Factors like leg length, saddle setback, and pedaling style must also be considered.
Too Short, Too Fast: Extremely short cranks can lead to excessive cadence, reducing torque and potentially overloading the cardiovascular system.
Power Compromise: For larger athletes with longer femurs, the leverage loss from shorter cranks may outweigh the aerodynamic and vascular benefits.
Our Process
To ensure optimal results, we combine NIRS analysis, EMG monitoring, and aero testing. This allows us to pinpoint the exact crank length that maximizes power, minimizes oxygen loss, and maintains a sustainable aerodynamic position.
Key takeaways for time trialists and triathletes
Shorter cranks improve hip angle and blood flow, allowing for a more comfortable and sustainable aero position.
Muscle oxygenation and vascular efficiency can be monitored with NIRS to fine-tune crank length for maximum performance.
Not all riders benefit equally from shorter cranks—careful analysis of biomechanics and vascular data is essential.
The Industry Gap: Where Are the Options?
Despite the growing evidence, the cycling industry lags behind in offering shorter cranks. Major brands like Shimano and SRAM still prioritize 170–175 mm lengths, leaving shorter riders (under 1.65 m) to struggle with biomechanically inappropriate setups.
Smaller brands like Rotor and Cane Creek are filling the gap, but availability remains a challenge, particularly for amateurs.
Key takeaways for every cyclist
Shorter cranks reduce joint stress, particularly on knees and hips.
Power loss is negligible, and shorter cranks often improve overall efficiency.
Climbing efficiency improves, while sprinting performance requires careful adaptation.
Always choose crank length based on your biomechanics, not just trends.
Curious if shorter cranks are right for you?
Shorter cranks are not a magical solution. They must be carefully tailored to your unique body, riding style, and goals. Our technologies, including EMG and thermal imaging, help us make objective decisions about your crank length and bike setup. Book a bikefit today and let science guide your ride!
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