Crank Length
Biomechanical crank length from inseam and tibia — hip closure, knee tracking, and aero trade-offs.
Crank Length Optimization
Calculate your optimal crank arm length based on biomechanics. Targeting the right crank length improves hip angles, aerodynamics, and cadence efficiency.
1. Your Specs
Measure from the floor to your crotch while standing against a wall with your feet 6-8 inches apart.
Measure from the center of the bottom bracket (BB) to the top of the saddle along the seat tube.
Measure from the center of the ankle bone to the center of the knee joint. This provides a more accurate recommendation than inseam alone.
2. Discipline
3. Compare Length
Compare different crank lengths to see their impact on your biomechanics and leverage.
Rotate the crank to analyze knee and hip angles through different phases of the pedal stroke.
The angle of your foot relative to the ground. Toe-down (positive angle) is common at the bottom of the stroke.
Used to estimate your foot length, which affects the lever arm between the pedal and ankle joint.
Distance from the ball of the foot to the pedal axle. Moving the cleat back (positive) effectively shortens the leg reach.
Recommended Range
Endurance balance: Optimized for sustained high-rpm efforts in an aero tuck.
Breathing: Opens hip angle to facilitate diaphragm movement.
Pro Tip: "Anyone who can ride 170mm can ride 165mm. Going too long causes injury; going short just feels different."
When in doubt, round down.
Physics Trade-offs (vs 170mm)
*Compensate by shifting 1 gear easier.
Knee Angle Analysis
Good range. Low risk of knee issues.
Move the slider to compare vs 170mm baseline
Rule of thumb: Every 10mm change ≈ 3.5° knee angle change
Angles vs Recommendation
Related Simulations
Premium solvers
Validate fit changes against real CdA
Calibrate CdA from power rides, plan courses with your physics, or test velodrome setups in Track Lab.