Every cyclist knows that the smallest adjustments made to their bike can have the biggest impact on improving their performance. That’s why it's important to choose gear that aligns with your body proportions and riding goals. One key component of a bike that often goes unnoticed is the crank length. It may seem like a small detail, but the length of your crank significantly affects your cycling.
To further explain, in this article, we’ll go into detail about crank lengths and how to choose the best one for yourself.
How Does Crank Length Affect Cycling Performance?
Here’s how the crank length for a bicycle can affect your performance:
- Power Output: The length of the crank directly affects the amount of leverage a rider can apply to the pedals. Longer cranks tend to provide better leverage but can cause fatigue during long rides. In contrast, the shorter crank offers a higher cadence, allowing riders to sustain energy output over distances.
- Comfort and Fit: Properly fitted cranks also contribute to the comfort and ease of your riding experience. It reduces stress on your knees, hips, and lower back, allowing you to ride longer distances with less fatigue. Conversely, cranks that are too long or too short can have adverse effects on your body, even risking injury.
- Aerodynamics: This refers to how a cyclist’s body and bike interact with air resistance while riding. Since shorter cranks reduce the hip angle at the top of the pedal stroke, it allows riders to maintain a more aerodynamic posture. Longer cranks, however, limit flexibility, making it more challenging to achieve an aerodynamic position.
How To Choose Bicycle Crank Length?
What to consider when choosing a bicycle crank length:
1. Your Height and Leg Length
First and foremost, you must consider your height and leg length when choosing a crank. If the crank’s length happens to be too short or too long for your body, you’ll have trouble leveraging it and maintaining consistent speed. Overtime, you might even also develop strain or injury.
Generally, longer cranks are better suited for taller riders, just as shorter cranks work with shorter riders. If you want a more detailed reference, consider the following crank lengths:
- Short Riders (Under 5’6”):between 165mm and 170mm
- Average Riders (5’6” to 6’0”):around 170mm or 172.5mm
- Taller Riders (Over 6’0”):around 175mm or 180mm
2. Type of Riding
This refers to how you plan to ride your bike, whether it’s for scaling mountain trails or participating in competitive racing. Whatever type of riding you do, the length of the crank directly affects your bike’s efficiency and performance. To maximize both, here’s a breakdown of crank lengths for different cycling types:
- Road Biking: Shorter cranks (165mm–172.5mm) help with pedaling and reduce knee strain.
- Mountain Bikers: Longer cranks (175mm–180mm) provide better torque for technical climbs.
- Track Riders: Shorter cranks (165mm–170mm) improve aerodynamics and allow for a more aggressive positioning.
3. Pedal Stroke and Knee Health
The crank you choose can also have a significant effect on your knees, especially when it’s the wrong one. If so, you’ll likely experience knee pain, as it’s the second most reported overuse injury for cyclists.
This issue typically occurs when the crank is too long for your legs. Longer cranks increase the range of motion during each pedal stroke, causing your knee to bend more deeply and strain the joint. Instead, you can opt for a shorter crank that reduces the bend and allows for smoother pedaling.
4. Professional Bike Fit
A bike fit is a service where a professional modifies your bike according to your body proportions and riding goals. As you might’ve guessed by now, the fitter also takes the length of the crank into account. So, they’ll assess your overall flexibility, hip rotation, and riding posture to select the best crank for your cycling.
As a result, you’ll have a properly fitted crank that provides efficient pedaling, reduces the risk of injury, and maximizes comfort. The bike fit also assesses the saddle height and handlebar positioning so that they work in sync with the crank’s length.
Crank Length Formulas
Formulas are another way of determining the best crank for cycling. The results aren't always the most accurate, but they still provide a starting point for choosing a suitable length. Here are two effective methods you can try:
Method 1: Tibia Length Method
This method focuses on the length of your tibia, from the center of the ankle bone to the center of the knee joint. Measure the area and apply it to the following formula:
Crank Length=Tibia Length×0.41
For example, if your tibia length is 40cm, then:
Crank Length=40×0.41=16.4 cm
Which is further converted into 164 mm.
This calculation suggests that a crank length of about 164 mm would work best for you.
Method 2: Inseam Length Method
Another commonly used formula is the Inseam Length method. It measures the top of the inner thigh to the floor, while standing. Your back should be against the wall, and your feet should be about 6 inches apart before you take the measurement. Then, apply it to the following formula:
Crank Length= Inseam×0.216
For example, if your inseam is 80 cm, then:
Crank Length= 80×0.216=17.28 cm
Which is further converted into 172.8 mm
This calculation suggests that a crank length of about 172.8 mm would work best for you.
FAQs
What Are the Standard Crank Lengths?
The three most common crank lengths for bicycles are 170mm, 172.5mm and 175mm. The specific length of the crank also depends on the size of the frame. For instance, small bikes tend to come with 170mm cranks.
How Do I Know My Current Crank Length is Wrong For Me?
If your current crank length is wrong, you’ll likely feel discomfort or pain in the knees, hips, or lower back. You might also experience performance issues like inefficient pedaling, difficulty maintaining cadence, etc.
How is the Length of a Crank Measured?
The length of a crank is determined by measuring from the center of the bottom bracket to the center of the pedal axle along the crank arm.
Conclusion
Choosing the right crank length is the key to improving your cycling performance, pedaling efficiency and comfort. To find the best length, consider factors like height, riding style, and knee health. Furthermore, you can consult a professional bike fit or use formulas to find your ideal length.
If you’re interested in learning more about cycling and bike gear, check us out at ROCKBROS. We cater to cyclists of all skills, from casual commuters to dedicated athletes.
