165mm Cranks: Benefits, Drawbacks, and Who Should Consider Them

Should I go to 165mm cranks?

Switching to 165mm cranks can offer specific biomechanical advantages, particularly for reducing joint stress and facilitating higher cadences, but the optimal crank length is highly individual and necessitates careful consideration of your anatomy, riding style, and specific goals.

What Are Bicycle Crank Arms and Why Does Length Matter?

Bicycle crank arms are the levers that connect your pedals to the bike's bottom bracket, translating the force from your legs into rotational motion that drives the chain. Their length is measured from the center of the pedal spindle to the center of the bottom bracket spindle. Common lengths range from 165mm to 175mm, with custom options extending beyond this.

The length of your crank arms directly influences several critical aspects of your cycling biomechanics:

• Leverage and Torque: Longer cranks provide more leverage, theoretically making it easier to push a larger gear at a lower cadence. Shorter cranks offer less leverage.
• Cadence Potential: Shorter cranks reduce the circumference of the pedal stroke, allowing for faster leg speed and potentially higher cadences with less effort.
• Joint Angles: Crank length significantly impacts the peak flexion and extension angles of your hips, knees, and ankles throughout the pedal stroke.
• Power Output: Power is the product of force and angular velocity (cadence). Changes in crank length can alter the optimal balance between these two factors for an individual.

Biomechanics of Crank Length: The Core Principles

Understanding the fundamental biomechanical trade-offs is crucial when considering crank length adjustments:

• Leverage vs. Cadence: This is the primary seesaw. Longer cranks provide more leverage, which can be advantageous for lower cadence, high-force efforts (e.g., climbing steep hills in a big gear). Shorter cranks reduce the leg's travel distance per revolution, making it easier to maintain a higher cadence, which can be more efficient for some riders and power profiles.
• Joint Angles and Comfort: The most compelling argument for shorter cranks often revolves around joint health. A shorter crank arm reduces the maximum flexion angle at the hip and knee during the upstroke. For individuals with hip impingement, deep hip flexor tightness, patellofemoral pain, or other knee issues exacerbated by extreme flexion, shorter cranks can significantly improve comfort and reduce stress.
• Power Output: While longer cranks offer more leverage, they also require the foot to travel a greater distance per revolution. Shorter cranks require more force per revolution to generate the same torque, but they allow for higher cadences. The total power output (Force x Velocity) is ultimately determined by the rider's physiological capacity and their ability to apply force efficiently at a given cadence. There is no definitive evidence that one crank length inherently produces more power for all riders; rather, it shifts the optimal force-cadence balance.

The Case for Shorter Cranks (e.g., 165mm)

Transitioning to 165mm cranks, or other shorter lengths, offers several potential benefits:

• Reduced Joint Stress: As mentioned, the primary benefit for many riders is the reduction in peak hip and knee flexion. This can alleviate pain associated with hip impingement, deep hip flexor tightness, patellofemoral pain syndrome, and other conditions aggravated by extreme joint angles.
• Improved Aerodynamics: For time trialists and triathletes, shorter cranks can allow for a more aggressive, lower handlebar position. With less knee lift at the top of the pedal stroke, riders can often rotate their pelvis further forward and lower their upper body, reducing frontal area and improving aerodynamic efficiency.
• Higher Cadence Potential: Shorter cranks make it easier to spin at higher RPMs. This can be beneficial for riders who prefer a higher cadence riding style, as it can distribute muscular effort more evenly and potentially reduce fatigue in specific muscle groups.
• Reduced Pedal Strike Risk: Especially relevant for fixed-gear riders, track cyclists, or those riding bikes with very low bottom brackets (e.g., some crit bikes), shorter cranks provide more ground clearance, reducing the risk of pedals striking the ground during cornering.
• Better Fit for Shorter Riders: While not exclusively for them, individuals with shorter inseams or proportionally shorter femurs may find shorter cranks allow for a more natural and comfortable pedal stroke, preventing over-extension at the bottom and excessive flexion at the top.

Potential Drawbacks and Considerations

While beneficial for many, shorter cranks are not a universal solution and come with their own considerations:

• Loss of Leverage/Torque: For riders accustomed to pushing big gears at low cadences, the immediate sensation might be a loss of leverage. This can require a period of adaptation where the rider learns to apply more force per revolution or adjusts to riding at a slightly higher cadence.
• Adaptation Period: Your body has developed muscle memory and neural pathways optimized for your current crank length. Switching will require an adaptation period where your muscles, nervous system, and cardiovascular system adjust to the new biomechanics. This can initially feel awkward or even lead to temporary fatigue in different muscle groups.
• Saddle Height Adjustment: Crucially, when switching to shorter cranks, your saddle will need to be raised by the exact difference in crank length to maintain proper leg extension at the bottom of the pedal stroke (e.g., from 170mm to 165mm means raising the saddle by 5mm). Neglecting this will lead to under-extension and lost power.
• Power Profile Shift: Riders who are naturally "grinders" (low cadence, high force) might find it challenging to adapt to the higher cadence required to maintain similar power output with shorter cranks.
• Cost: Cranksets are a significant investment. Making a switch purely for marginal gains without a clear biomechanical reason might not be justified for all riders.

Who Might Benefit from 165mm Cranks?

Consider 165mm cranks if you fall into one or more of these categories:

• Riders Experiencing Joint Pain: Especially hip pain (impingement, deep hip flexor issues) or knee pain (patellofemoral syndrome) that worsens at the top of the pedal stroke.
• Triathletes and Time Trialists: Seeking to optimize their aerodynamic position and maintain power in an aggressive tuck.
• Track or Criterium Racers: Where high cadence and ground clearance are paramount.
• Riders Seeking Higher Cadence: Those who want to train or race at a higher RPM to improve efficiency or reduce muscular fatigue.
• Individuals with Specific Anatomical Limitations: Such as proportionally shorter femurs or limited range of motion in the hips or knees.
• Shorter Riders: While not a strict rule, shorter riders often find 165mm cranks provide a more comfortable and efficient fit.

How to Determine Your Optimal Crank Length

There is no single formula that dictates the perfect crank length for everyone. It's a highly individualized choice influenced by:

• Body Proportions: While inseam length is a starting point, femur length plays a more significant role in determining optimal hip and knee angles.
• Riding Style and Discipline: A track sprinter might prioritize different characteristics than an ultra-endurance mountain biker.
• Current Issues: Persistent pain or discomfort on the bike is a strong indicator that your current setup, including crank length, may not be optimal.
• Professional Bike Fit: The most reliable way to determine your optimal crank length is through a comprehensive professional bike fit. An experienced fitter will analyze your biomechanics, flexibility, riding goals, and current issues to recommend appropriate adjustments, often using adjustable crank arms for testing.
• Trial and Error (Cautiously): If a professional fit isn't immediately feasible, and you have access, trying different crank lengths can provide valuable personal feedback. However, always make small, informed adjustments and allow your body time to adapt.

Making the Switch: What to Expect

If you decide to make the switch to 165mm cranks, be prepared for:

• Saddle Height Adjustment: This is non-negotiable. Raise your saddle by the exact difference in crank length (e.g., 5mm if going from 170mm to 165mm). You may also need to adjust saddle fore-aft slightly.
• Adaptation Period: Expect an initial period (days to weeks) where your pedal stroke feels different, potentially awkward, or less powerful. Your muscles will need to adapt to the new range of motion and force application.
• Monitor Progress: Pay close attention to how your body feels. Are joint pains reduced? Is your cadence naturally higher? Is your power output maintained or improved? Don't be discouraged by initial sensations; allow for adaptation.
• Gradual Transition (If Possible): Some riders find it helpful to transition gradually, perhaps by trying the shorter cranks on an indoor trainer first, or for shorter rides, before committing fully.

Conclusion: Is 165mm Right for You?

Ultimately, the decision to switch to 165mm cranks is a personal one, best made with an understanding of your own body, riding goals, and biomechanical needs. While shorter cranks offer compelling advantages for reducing joint stress, improving aerodynamics, and facilitating higher cadences, they are not a universal panacea. For many, a professional bike fit is the most effective way to determine if 165mm cranks are the optimal choice to enhance comfort, efficiency, and performance on the bike.