What size cranks are best for me?
When it comes to optimizing your cycling performance and comfort, crank length is one of the most debated but also overlooked components of a bike fit. While most cyclists accept whatever cranks come stock on their bike, choosing the right crank length can significantly impact your pedaling efficiency, power output, and injury prevention.
What is Crank Length?
Crank length is the distance from the center of the bottom bracket to the center of the pedal spindle, measured in millimeters. Standard crank lengths typically range from 165mm to 180mm, with 170mm and 172.5mm being the most common sizes.
Why Crank Length matters?
The length of your cranks affects several key aspects of your cycling:
Leverage and Power: Longer cranks provide more leverage, potentially allowing you to generate more torque. However, this comes at the cost of requiring a larger range of motion at the hip and knee.
Cadence: Shorter cranks generally allow for a higher, smoother cadence since your legs travel through a smaller circle with each pedal stroke.
Biomechanics: Crank length directly impacts hip and knee angles at the top and bottom of your pedal stroke. Incorrect length can lead to overextension or excessive flexion, increasing injury risk.
Traditional Sizing Guidelines
The most common method for selecting crank length is based on inseam measurement. The overall height of the rider is only a secondary aspect to look at.
26-29” inseam / 4’10 to 5’4”: 160mm cranks
28-30” inseam / 5'0 to 5'3: 165mm cranks
31-33” inseam / 5'6 to 5'10: 170mm cranks
32-35” inseam / 5'8 to 6'0: 172.5mm cranks
34-37” inseam / 6'0 and taller : 175mm or 180mm cranks
However, these are just starting points. Individual biomechanics, flexibility, riding style, and your cycling discipline all play important roles.
What does the Science say:
Research by Dr. Jim Martin and Dr. W.W. Spirduso (2001, 2002) at the University of Utah debunked the myth that longer cranks produce more power, showing that max power is generally unchanged for cranks between 145mm and 195mm. Their studies suggest an optimal length is roughly 20% of leg length or 41% of tibia length. Full text here: “Determinants of maximal cycling power: crank length, pedaling rate and pedal speed”
Considerations by Discipline
Road Cycling: Most road cyclists benefit from standard lengths (170-175mm) that balance power and cadence for varied terrain.
Time Trial/Triathlon: Many athletes prefer slightly shorter cranks (160-170mm) to maintain a higher cadence and reduce hip angle closure in an aggressive aero position.
Mountain Biking: Shorter cranks (165-170mm) are becoming increasingly popular to improve ground clearance on technical terrain and allow for better bike maneuverability.
Track Cycling: Traditionally, riders often use longer cranks (175-180mm) to maximize power output during short, high-intensity efforts.
Signs your Crank Length may be wrong:
You may benefit from different (= shorter) crank length if you experience:
Knee pain, especially at the top or bottom of the pedal stroke
Hip discomfort or restricted hip flexion at the top of the stroke
Difficulty maintaining a smooth, high cadence
Excessive rocking in the saddle
Discomfort in an aero position (for triathletes and time trialists)
The Modern Approach: Shorter May Be Better
Recent research and anecdotal evidence from professional fitters suggest that many cyclists are riding cranks that are too long. Shorter cranks can offer several advantages:
Reduced stress on knees and hips
Improved pedaling smoothness
Better fit in aerodynamic positions
Enhanced bike handling and cornering clearance (especially for Criterium racers)
Reduced fatigue on longer rides
Many cyclists who drop down 2.5 or 5mm in crank length report immediate improvements in comfort with no noticeable loss in power.
How to Test and Choose
If you're considering a crank length change, here's how to approach it:
Get a Professional Bike Fit: A qualified fitter can assess your biomechanics and recommend optimal crank length based on your flexibility, riding style, and goals.
Consider Your Flexibility: Less flexible riders often benefit from shorter cranks to reduce the range of motion required.
Try Before You Buy: If possible, test ride bikes or use a trainer with adjustable cranks to feel the difference.
Make Small Changes: If experimenting on your own, change by only 2.5-5mm at a time and give yourself several rides to adapt.
Monitor Your Metrics: Pay attention to comfort, power output, and cadence during your test period.
Final Thoughts
While crank length might seem like a minor detail, it can have a meaningful impact on your cycling experience. The "standard" sizing charts are a reasonable starting point, but don't be afraid to experiment, especially if you're experiencing discomfort or seeking marginal gains in performance.
Remember, the best crank length is the one that allows you to pedal efficiently, comfortably, and powerfully for your specific discipline and body. When in doubt, consult with a professional bike fitter who can provide personalized recommendations based on your unique biomechanics and cycling goals.
Ready to optimize your bike fit? Contact us for a comprehensive bike fitting session and personalized coaching to help you ride faster, longer, and more comfortably.