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Crank length? What about it?

Crank length in cycling is an important aspect of bike fit and performance. The crank is the part of a bicycle that connects the pedal to the bottom bracket, and its length can vary significantly. Here's a detailed look at why different crank lengths exist and the research surrounding their impact.

Reasons for Different Crank Lengths

  1. Rider Anatomy: The most obvious reason for different crank lengths is the variation in rider leg length. A longer leg might be more comfortably and effectively accommodated with a longer crank to match the larger range of motion.

  2. Bike Fit and Comfort: Crank length affects the angle of the hip, knee, and ankle at various points in the pedaling cycle. A crank that is too long can lead to excessive bending and stretching, which can be uncomfortable or even injurious. Conversely, a crank that is too short might not allow for efficient power transfer because the legs are not fully extended.

  3. Riding Style and Discipline: Different cycling disciplines may benefit from different crank lengths. For instance, track cyclists often prefer shorter cranks to allow for quicker revolutions and faster accelerations, whereas a mountain biker might prefer longer cranks to leverage more torque when climbing steep terrain.

  4. Performance: Some studies suggest that crank length can influence performance by affecting the mechanical efficiency of pedaling, the power output, and the aerobic demand of cycling. The optimal crank length can help in maximizing the force production during pedaling.

Research on Crank Length

The research on crank length is extensive yet somewhat inconclusive, largely because the optimal crank length can be highly individual. Here are some key points from the research:

  • Power Output: Studies have shown that crank length has a relatively small effect on overall power output. A study by Jim Martin from the University of Utah found that variations in crank length (from 145mm to 195mm) resulted in less than 1% variation in maximum power output.

  • Cadence and Efficiency: Shorter cranks tend to support a higher cadence, which some riders find more efficient, especially over long distances where energy preservation is crucial. However, longer cranks can offer more leverage, which is beneficial in situations requiring high torque, like climbing.

  • Comfort and Injury Prevention: Research indicates that crank length can influence joint angles significantly. A crank that is too long can increase the risk of knee injuries due to the higher angles involved, whereas a crank that is too short might lead to underutilization of the leg muscles.

  • Aerodynamics: In disciplines like time-trialing, shorter cranks can allow the rider to adopt a more aerodynamic position by lowering the hip angle at the top of the pedal stroke.

Despite the wealth of studies, there is no one-size-fits-all answer when it comes to the best crank length. It often comes down to personal preference, comfort, and the specific demands of the cyclist's preferred riding style and discipline. Bike fitting experts typically use a range of methods, including rider feedback and biomechanical assessments, to determine the most appropriate crank length for an individual.

When considering crank length for your cycling setup, shorter cranks offer several benefits that might align with your cycling goals and preferences. Here’s how you can benefit from opting for a shorter crank:

Increased Comfort and Reduced Injury Risk

Shorter cranks can reduce the acute angles your knees and hips have to navigate during the pedal stroke, which may decrease the strain on these joints. This can lead to improved comfort over long rides and a reduced risk of repetitive strain injuries. If you've experienced discomfort or injuries with longer cranks, shorter ones might alleviate these issues by offering a gentler range of motion.

Enhanced Cadence and Efficiency

If you prefer a higher cadence, shorter cranks facilitate quicker pedal turnover. This can be particularly beneficial during long-distance rides or races where maintaining a high cadence could help conserve energy by relying more on aerobic endurance rather than muscular force. A higher cadence with shorter cranks also helps in maintaining speed without excessive muscle fatigue.

Improved Bike Handling

Shorter cranks can improve your bike's handling, especially in tight corners or technical sections where pedal clearance is crucial. This is particularly relevant in mountain biking and cyclocross where striking a pedal on the ground can lead to crashes or loss of control. Shorter cranks reduce the likelihood of pedal strikes when navigating uneven terrain.

Better Suitability for High-Intensity Efforts

For disciplines like criterium racing or track cycling, where quick accelerations and sprints are frequent, shorter cranks can enable you to accelerate faster. The reduced length allows for a more rapid response when you need to suddenly increase your pedaling speed, which can be crucial in competitive scenarios.

Aerodynamic Advantages

Shorter cranks can also contribute to a more compact and aerodynamic riding position. By lowering the height of your knees during the pedal stroke, you can reduce your frontal area and improve your overall aerodynamics. This is especially beneficial in time trials and triathlons where every bit of aerodynamic efficiency counts.

While shorter cranks offer these benefits, it's essential to consider how they fit into your overall riding style and physical needs. Testing different crank lengths or consulting with a bike fitting expert can provide personalized insights into what works best for you.

Longer crank lengths, typically considered more "standard" in the range of about 170mm to 175mm for most adult bikes, are prevalent for several reasons. These standard lengths have become the norm due to a combination of historical precedence, biomechanical theories, and practical advantages for a broad range of riders. Here's why longer crank lengths are commonly used:

Leverage and Torque

One of the primary reasons for using longer cranks is the increased leverage they provide. Leverage is crucial for producing torque, which is the force that turns the pedals. With a longer crank, you can apply force over a longer distance, effectively increasing torque with the same amount of force from your legs. This is particularly advantageous when you need to pedal slowly but powerfully, such as when climbing hills or riding through rough terrain.

Muscle Utilization

Longer cranks allow for a greater range of motion in your leg during each pedal stroke, which can lead to more effective use of your leg muscles, including the quadriceps, hamstrings, and glutes. This extended range of motion can help in engaging the muscles more thoroughly, potentially leading to greater force production, especially in situations where each pedal stroke needs to count, like in steep ascents.

Compatibility with Most Riders

The "standard" crank lengths have been established based on the average leg lengths and biomechanics of the general cycling population. These lengths tend to fit a wide range of riders adequately, ensuring that most people can ride comfortably without the need for specialized adjustments. This general compatibility simplifies the manufacturing and fitting processes for bikes, making it easier for bike shops to stock and sell bikes without requiring extensive customization.

Historical and Practical Considerations

The cycling industry has standardized certain components, including crank lengths, based on what has traditionally been popular and practical. Longer crank lengths have been in use for many years, and much of the existing research and design in cycling ergonomics has been built around these measurements. As a result, many training techniques, performance strategies, and ergonomic assessments are tailored to these standard sizes.

Power Output at Lower Cadences

For certain types of cycling, such as time-trialing or loaded touring, the ability to maintain a strong, steady power output at a lower cadence can be beneficial. Longer cranks can be advantageous in these situations because they allow for more forceful pedal strokes, which can be maintained without requiring excessive speed in the pedaling motion.

Despite the advantages of longer cranks, it's important to note that they are not universally ideal for all riders or all cycling situations. Just as with shorter cranks, the best crank length for you depends on your body dimensions, riding style, and personal preferences. Consulting with a bike fitting expert can help you determine the most appropriate crank length for your needs.

The science surrounding optimal crank length in cycling continues to evolve, and recent studies have begun to challenge some of the traditional assumptions. Here’s an overview of the current understanding, what professional cyclists tend to use, and the general recommendations from bike fitters and coaches:

Recent Scientific Insights

Recent research suggests that the impact of crank length on power, efficiency, and comfort may not be as significant as previously thought. Some studies have found that changes in crank length (within a reasonable range) do not significantly affect overall cycling efficiency or power output. The consensus is increasingly that personal comfort and biomechanical efficiency are more critical than adhering to any specific crank length.

For instance, a notable study by Jim Martin found that variations in crank length (ranging from 145mm to 195mm) resulted in less than 1% difference in power output, suggesting that cyclists may not need to be as concerned with finding an "optimal" crank length, and should instead focus on what feels best for their riding style and body.

What Professional Cyclists Use

Professional cyclists often use crank lengths that are tailored to their specific needs, based on their body measurements, the discipline they compete in, and personal preferences. In road cycling, common crank lengths range from 170mm to 175mm. However, in track cycling, where quick acceleration and high cadence are crucial, shorter cranks (sometimes as short as 165mm) are often used to allow for faster spinning and better acceleration. In time trials and triathlons, athletes might opt for slightly shorter cranks to maintain a more aerodynamic position and higher cadence.

Recommendations from Bike Fitters and Coaches

Most bike fitters and coaches recommend crank lengths based primarily on the rider's leg length and overall biomechanics, but they also consider the rider’s comfort, the type of cycling they do, and their performance goals. A good bike fit will typically involve dynamic testing, where the rider's performance and comfort are assessed in real riding conditions.

Bike fitters often use formulas as a starting point, which might suggest crank lengths based on inseam measurements, but these are increasingly seen as guidelines rather than strict rules. The trend is moving towards a more holistic approach, considering factors like rider comfort, joint health, and performance metrics.

In conclusion, while there is no one-size-fits-all answer, the approach to selecting crank length is becoming more personalized. The focus is shifting from traditional norms to what actually works best for the individual cyclist in their specific context. Whether shorter or longer cranks are "better" is less about universal truths and more about individual optimization.

Switching crank sizes is an option many cyclists consider, either to improve comfort, enhance performance, or address specific issues such as joint pain or inefficiencies in their pedal stroke. The science of switching crank sizes supports the idea that it can be beneficial but with some caveats regarding adaptation and fit.

Adaptation to New Crank Lengths

The human body is quite adaptable, and most cyclists can adjust to a new crank length with some time. Studies indicate that changes in muscle activation patterns occur when altering crank length, but these adjustments typically stabilize after a period of acclimatization. The time it takes to adapt can vary based on the extent of the change and the individual cyclist's condition and experience.

Impact on Biomechanics

Changing crank lengths can significantly affect your bike's biomechanics. A longer crank increases the range of motion required at the hip, knee, and ankle joints. This can be beneficial for leverage and power on steep climbs but may increase the strain on these joints, potentially leading to discomfort or injury if not properly adjusted. Conversely, a shorter crank reduces the range of motion, which can help decrease joint stress and increase cadence, beneficial for high-speed cycling and reducing fatigue over long distances.

Performance Considerations

Research shows that while crank length can influence performance aspects such as power output and efficiency, these effects are relatively small within a reasonable range of lengths (e.g., 165mm to 175mm). The choice between longer and shorter cranks should consider the type of riding, the cyclist’s physical attributes, and personal preferences. For instance, a shorter crank might be preferred for activities requiring high cadence and quick accelerations, whereas a longer crank might be better for maximizing torque and power in climbing.


  1. Consult a Professional: Before changing crank lengths, it's wise to consult with a bike fitting professional. They can assess your current setup and recommend changes based on your biomechanics, riding style, and any discomfort or performance issues you're experiencing.

  2. Gradual Transition: If you decide to change your crank length, it's advisable to transition gradually if possible. This might involve increasing or decreasing in small increments to allow your body to adapt without risking injury.

  3. Monitor and Adjust: Pay close attention to how your body responds to the new crank length. Look for signs of improved comfort or performance, but also be vigilant about any new pain or discomfort, which could indicate that further adjustments are needed.

In summary, switching crank sizes is generally safe and can be beneficial, provided it's done thoughtfully and with attention to individual needs. The science supports flexibility in crank length choices, emphasizing personal adaptation and comfort over rigid standards.



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