If you’re a cyclist, you know that every component of your bike plays a crucial role in your performance and comfort on the road. One such component that often gets overlooked is the crank arm length.
The crank arm length refers to the distance from the center of the crank axle to the center of the pedal spindle. Crank arm length is typically measured in millimeters (mm) and can range from as short as 165mm to as long as 180mm or more. It’s an important measurement to consider when setting up your bike for optimal efficiency and power transfer.
So, what is the best crank arm length for cycling? Well, the answer isn’t one-size-fits-all. It depends on various factors such as your body proportions, riding style, and the type of cycling you do. In this article, we’ll dive deeper into the topic, explaining the importance of crank arm length and how to choose the right one for you.
Why Crank Arm Length Matters
The length of your crank arms can have a significant impact on your pedaling efficiency, aerodynamics, comfort, and injury prevention.
How Crank Arm Length Affects Pedaling Efficiency and Power Output
One of the primary ways crank arm length influences cycling performance is through pedaling efficiency and power output. Let’s dive deeper into how shorter and longer crank arms affect these factors.
Shorter crank arms allow you to pedal faster with less effort. This is because shorter cranks reduce the dead spot in the pedal stroke, which is the point when one foot is at the top of the stroke and the other is at the bottom. By minimizing this dead spot, shorter cranks enable a more continuous and efficient pedal stroke.
Additionally, shorter crank arms can increase your cadence, which is the number of pedal revolutions per minute. A higher cadence is often associated with better endurance and efficiency, as it allows you to distribute the workload more evenly among your muscles. With shorter cranks, you can spin your legs faster, helping you maintain a higher cadence and ultimately improving your pedaling efficiency.
On the other hand, longer crank arms offer increased torque and leverage, allowing you to pedal harder and generate more power. This can be beneficial for activities that require bursts of power, such as sprinting or climbing steep hills. The increased leverage provided by longer cranks allows you to exert more force on the pedals, generating greater torque and propelling you forward with more force.
However, it’s important to note that longer cranks also come with some drawbacks. Longer crank arms require more work to complete a full pedal stroke compared to shorter cranks. This increased range of motion can lead to higher fatigue levels over longer distances, as well as increased oxygen consumption. Therefore, while longer cranks can provide more power, they may also contribute to faster fatigue during extended rides.
How Crank Arm Length Affects Aerodynamics and Speed
Crank arm length also has an impact on aerodynamics and speed. The length of your crank arms affects your riding position, frontal area, and drag coefficient.
With longer crank arms, your saddle height needs to be higher to accommodate your leg extension. This raises your center of gravity and increases your frontal area, which can negatively affect your aerodynamics. On the other hand, shorter crank arms allow for a lower saddle height, reducing your center of gravity and minimizing your frontal area, resulting in improved aerodynamics.
Additionally, longer crank arms can increase the ground clearance and cornering ability of your bike. This can be advantageous for riders who prioritize maneuverability and stability in tight turns.
How Crank Arm Length Affects Comfort and Injury Prevention
To understand how crank arm length affects comfort and injury prevention, we need to look at how it influences the bike fit. Crank arm length plays a role in determining saddle height, knee angle, hip angle, and reach.
When it comes to saddle height, shorter crank arms allow for a lower saddle height, while longer crank arms require a higher saddle position. Adjusting the saddle height according to the crank arm length ensures proper leg extension and prevents strain on the knees.
The knee angle is also affected by crank arm length. Longer crank arms result in a narrower knee angle, while shorter crank arms create a wider knee angle. Finding the right balance is crucial to prevent knee pain and discomfort.
Hip angle is another factor influenced by crank arm length. Longer crank arms tend to open up the hip angle, while shorter crank arms result in a more closed hip angle. The hip angle affects your power output and overall efficiency on the bike.
Lastly, crank arm length can impact your reach on the bike. Longer crank arms may require a shorter stem or a more aggressive riding position, while shorter crank arms might allow for a more relaxed and upright posture.
Now that we understand how crank arm length affects various aspects of bike fit, let’s talk about how to adjust it according to personal preference and body mechanics. Finding the right crank arm length is a matter of trial and error, as it varies from person to person.
If you’re experiencing discomfort or pain in your knees, hips, back, or ankles, it might be worth considering a change in crank arm length. Consulting with a professional bike fitter can be incredibly helpful in determining the optimal crank arm length for your body.
The length of your crank arms can also influence the risk of overuse injuries and muscle fatigue. The longer the crank arm, the more range of motion your hips, knees, and ankles have to go through during each pedal stroke. This increased range of motion puts more stress on your joints and muscles, potentially leading to overuse injuries.
On the other hand, shorter crank arms limit your joint angles, reducing the risk of overuse injuries and muscle fatigue. However, it’s important to strike a balance between range of motion and joint loading to prevent excessive strain and inflammation on your tissues.
How to Measure Your Crank Arm Length
Measuring your crank arm length is a relatively simple process. All you need is a ruler or a tape measure. Here’s a step-by-step guide:
1. Find the center of your bottom bracket: The bottom bracket is the cylindrical housing that holds the crankset. You can usually find it at the base of the frame where the two crank arms meet. The center of the bottom bracket is the starting point for measuring your crank arm length.
2. Measure to the center of the pedal axle: Place one end of the ruler or tape measure at the center of the bottom bracket and extend it to the center of the pedal axle. Make sure the ruler or tape measure is straight and parallel to the ground.
3. Note the measurement: The measurement should be in millimeters (mm) or centimeters (cm). Common crank arm lengths range from 165 mm to 175 mm, but there are also other sizes available, such as 150 mm, 160 mm, 167.5 mm, 180 mm, and 190 mm.
Are Short Crank Arm Lengths Better
Shorter crank arm lengths have their advantages and disadvantages. They can provide faster cadence, reduce stress on your knees and lower back, improve aerodynamics and cornering clearance, and are suitable for climbing, sprinting, and spinning. However, they may decrease torque and leverage, require higher gearing or more effort to maintain speed, feel less stable or comfortable for some riders, and be less common or harder to find for certain bikes or components.
Here are the details.
Advantages of Shorter Crank Arm Lengths
1. Faster Cadence and Smoother Pedaling
Shorter crank arms allow for a faster cadence, which means you can spin your pedals more quickly. This can be advantageous in various situations, such as climbing steep hills or sprinting. With a faster cadence, you’ll maintain a smoother pedaling motion, reducing the strain on your muscles and joints.
2. Reduced Stress on Knees and Lower Back
Shorter crank arms can help reduce stress on your knees and lower back. By shortening the lever arm, you decrease the range of motion required for each pedal stroke. This can be beneficial for riders who have knee or lower back issues, as it reduces the strain on these areas.
3. Improved Aerodynamics and Cornering Clearance
Shorter crank arms can improve your aerodynamics on the bike. With a shorter lever arm, your body position can become more streamlined, reducing wind resistance. Additionally, shorter crank arms provide more clearance when cornering, allowing you to lean into turns without the risk of hitting your pedals on the ground.
4. Suitable for Climbing, Sprinting, and Spinning
If you enjoy climbing hills, sprinting, or participating in spinning classes, shorter crank arms may be a better choice. The faster cadence and reduced stress on your muscles make these activities more efficient and comfortable.
Disadvantages of Shorter Crank Arm Lengths
1. Decreased Torque and Leverage
One potential disadvantage of shorter crank arms is a decrease in torque and leverage. With a shorter lever arm, you may lose some power when pedaling, especially in situations that require a lot of force, such as sprinting or hill climbing.
2. Higher Gearing or More Effort to Maintain Speed
Shorter crank arms may require higher gearing or more effort to maintain the same speed as longer crank arms. This can be a potential drawback, especially if you prefer a more relaxed and comfortable ride. You may find yourself having to work harder to keep up with your usual pace.
3. Less Stability and Comfort for Some Riders
Shorter crank arms may feel less stable or comfortable for some riders, particularly taller individuals or those with long legs. The shorter length can affect the bike’s handling and stability, potentially causing discomfort or a less secure feeling while riding.
4. Availability and Compatibility
Shorter crank arm lengths are less common and may be harder to find for certain bikes or components. It’s important to ensure that the crank arm length you choose is compatible with your bike’s bottom bracket and other drivetrain components.
Are Long Crank Arm Lengths Better
Just like the short crank arm lengths, the long crank arm lengths also come with both pros and cons in many ways.
Advantages of Longer Crank Arm Lengths
1. Increased Torque and Leverage: Longer crank arms offer increased leverage, allowing you to generate more torque with each pedal stroke. This can be particularly beneficial for riders who tackle challenging terrains, such as steep climbs or off-road trails.
2. Lower Gearing for Easier Pedaling: Longer crank arms effectively lower the gearing of your bike, making it easier to pedal at lower speeds. This can be advantageous for beginners or riders who prefer a more relaxed pace.
3. Potential Power Output and Efficiency Boost: Some studies suggest that longer crank arms may enhance power output and efficiency for certain riders. However, it’s important to note that the impact can vary depending on individual factors such as leg length, riding style, and body mechanics.
4. Availability and Compatibility: Longer crank arm lengths are more common and easier to find for certain bikes or components. If you have specific compatibility requirements, opting for longer crank arms may give you more options to choose from.
Disadvantages of Longer Crank Arm Lengths
1. Reduced Cadence and Smoothness of Pedaling: Longer crank arms can make it more challenging to maintain a high cadence, which refers to the number of pedal revolutions per minute. This can result in a less smooth pedaling motion and may require some adjustment to your riding style.
2. Increased Stress on Joints and Lower Back: Longer crank arms can increase stress on the knees and lower back, especially if your bike fit is not properly adjusted. It’s crucial to ensure that your bike is set up correctly to minimize the risk of overuse injuries.
3. Compromised Aerodynamics and Cornering Clearance: Longer crank arms can compromise aerodynamics, as they create a larger frontal area. This might be a concern for riders who prioritize speed or plan to compete in time trials or triathlons. Additionally, longer crank arms can reduce cornering clearance, potentially impacting your ability to navigate tight turns.
4. Less Suitable for Climbing, Sprinting, and Spinning: Longer crank arms may not be ideal for riders who frequently engage in climbing, sprinting, or spinning. These activities often require quicker cadences and more explosive power, which can be more challenging with longer crank arms.
How to Choose the Right Crank Arm Length for Your Bike
Choosing the right crank arm length for your bike is an important decision that can greatly impact your cycling experience. Even though there is no definitive answer to what is the best crank arm length for cycling, as different lengths have their pros and cons, which we have shown you in above two sections, and may suit different riders and situations, there are some general guidelines and factors that you can consider when making your choice.
Factor 1: Your Height and Leg Length
Your height and leg length are important factors that affect your optimal crank arm length. Generally speaking, taller riders with longer legs may benefit from longer cranks, while shorter riders with shorter legs may prefer shorter cranks. This is because longer cranks can provide more leverage and torque for taller riders, while shorter cranks can reduce the knee angle and stress for shorter riders.
A simple way to calculate your ideal crank arm length based on your height is to use this formula: Crank arm length (mm) = Height (cm) x 0.095. For example, if you are 180 cm tall, your estimated ideal crank arm length would be: 180 cm x 0.095 = 171 mm. You can then round up or down to the nearest standard size, such as 165 mm, 170 mm, etc.
Another way to estimate your ideal crank arm length based on your inseam length is to use this formula: Crank arm length (mm) = Inseam length (cm) x 0.216. For example, if your inseam length is 80 cm, your estimated ideal crank arm length would be: 80 cm x 0.216 = 168 mm. Again, you can round up or down to the nearest standard size.
To measure your inseam length, you can use a wall and a book. Stand barefoot with your back against a wall and place a book between your legs as high as possible. Mark the top of the book on the wall with a pencil. Measure the distance from the floor to the mark with a tape measure. This is your leg length.
Factor 2: Your Riding Style and Discipline
Your riding style and discipline are also important factors that affect your optimal crank arm length. Different cycling disciplines require different crank arm lengths to maximize performance and efficiency.
Generally speaking, longer cranks may be more suitable for slower cadences and higher torque situations, such as climbing hills or sprinting. They provide increased power output and efficiency at lower cadences. On the other hand, shorter cranks may be more suitable for faster cadences and lower torque situations, such as time trials or flat roads. They reduce air resistance and fatigue at higher cadences.
Let’s break it down by discipline:
|Recommended Crank Arm Length
|170 mm – 175 mm
|165 mm – 170 mm
|165 mm – 167.5 mm
|165 mm – 170 mm
|170 mm – 172.5 mm
|170 mm – 175 mm
Factor 3: Your Personal Preference and Comfort
Your personal preference and comfort are other important factors that affect your optimal crank arm length. Ultimately, the best crank arm length for you is the one that feels the most comfortable and natural. You may have to experiment with different crank arm lengths to find the one that suits you best.
To determine your ideal crank arm length, you can consider the following methods:
1. Borrow or rent different bikes: Borrow or rent bikes with different crank arm lengths to see which one feels the most comfortable and efficient for you. Pay attention to how your body feels during and after the ride, particularly in your knees, hips, back, and ankles.
2. Swap cranks: If you already have a bike, you can try swapping your cranks with different sizes to see if it improves your comfort and performance. This is a cost-effective way to test different crank arm lengths without investing in a new bike.
3. Bike fit service: Consider getting a professional bike fit service. A bike fit expert can analyze your body position and pedaling mechanics to recommend the optimal crank arm length for you. They will take into account your body measurements, flexibility, riding style, and goals.
4. Crank length calculator: There are online crank length calculators available that take into account your body measurements and riding style to recommend an ideal crank arm length. While these calculators can provide a starting point, keep in mind that they are not foolproof and may not work for everyone.
If you’re experiencing any of the following signs, it may be an indication that you need to change your crank arm length:
- Pain or discomfort in your knees, hips, back, or ankles when cycling
- Difficulty maintaining a smooth and consistent cadence
- Trouble reaching or pushing the pedals
- Feeling too stretched or cramped on the bike
- Dissatisfaction with your cycling performance or efficiency
Remember, finding the right crank arm length is a personal journey. It may take some trial and error to find the perfect fit for you. Don’t be afraid to seek professional help or experiment with different lengths to optimize your cycling experience.
Choosing the right crank arm length is crucial for optimizing your cycling performance, comfort, and injury prevention. By considering your body proportions, riding style, and goals, and seeking professional advice if needed, you can find the crank arm length that suits you best. Remember to test different lengths to ensure the optimal fit. Ultimately, the right crank arm length will enhance your cycling experience and help you achieve your goals on the bicycle.
What crank arm length do you use and why? Share your thoughts and experiences in the comments below. If you enjoyed this article, please share it with your friends and fellow cyclists. Happy cycling!