Bicycle Conversion: Freewheel to Fixed Gear, Methods, and Safety Considerations

Can You Convert Freewheel to Fixed?

Yes, converting a freewheel bicycle to a fixed gear is technically possible, but it requires specific modifications and careful consideration of safety, component compatibility, and riding technique.

Understanding Freewheel vs. Fixed Gear

To understand the conversion process, it's essential to differentiate between the two drive systems:

• Freewheel Mechanism: A freewheel (or cassette) system allows the rider to coast without pedaling. The rear wheel continues to spin independently of the pedals, thanks to a ratcheting mechanism within the hub or cog. This is the standard setup for most multi-speed and many single-speed bicycles, offering the rider periods of rest and easier downhill navigation.
• Fixed Gear Mechanism: In a fixed gear system, the cog is rigidly attached to the rear wheel hub, meaning the pedals are directly linked to the rear wheel's rotation. If the rear wheel is moving, the pedals are moving. There is no coasting; to stop or slow down, the rider must resist the pedal rotation (skidding or track standing) in conjunction with braking. This direct connection offers a unique riding experience, often favored for its simplicity, efficiency, and the direct feedback it provides to the rider.

The Feasibility of Conversion: Is It Possible?

The short answer is yes, conversion is possible. However, it's not always straightforward, nor is it advisable for every bicycle or rider. The success and safety of a conversion depend heavily on the donor bike's frame geometry, dropout type, and the quality of the components used.

Key Considerations:

• Frame Compatibility: Frames designed for multi-speed freewheel systems often have vertical dropouts, which complicate chain tensioning—a critical aspect of fixed gear bikes.
• Component Reliability: The stresses on a fixed gear drivetrain are different and often higher than on a freewheel system, especially during braking (skidding).
• Rider Skill: Riding a fixed gear bike requires a different skill set and a period of adaptation.

Methods for Conversion

There are generally two primary methods to convert a freewheel bike to fixed gear, with varying degrees of safety and reliability:

Option 1: Fixed Cog on a Freewheel Hub (The "Suicide Hub")

This method involves threading a standard freewheel cog directly onto the freewheel threads of your existing rear hub, often secured with a bottom bracket lockring (which has a reverse thread).

• Mechanism: The idea is that the lockring, being reverse-threaded, will tighten as the cog tries to loosen under back-pedaling force.
• Risks and Limitations: This is widely known as a "suicide hub" for a reason. The threads on a freewheel hub are not designed for the immense, bidirectional torque of fixed gear riding. The lockring often isn't strong enough or doesn't have enough thread engagement to reliably hold the cog under significant back-pedaling or skidding forces. If the cog loosens or strips the threads, you instantly lose drive and, crucially, your primary means of slowing down (pedal resistance).
• Recommendation: This method is generally not recommended for any serious riding due to significant safety concerns. It might be used for very short, experimental rides on flat terrain with multiple redundant braking systems, but it is inherently unreliable.

Option 2: Dedicated Fixed Gear Hub (The Recommended Method)

The safest and most reliable method involves replacing your existing rear wheel or, at minimum, the rear hub with one specifically designed for fixed gear.

• Mechanism: A dedicated fixed gear hub has a primary set of threads for the fixed cog and a smaller, reverse-threaded section for a dedicated lockring. This lockring prevents the cog from unscrewing under back-pedaling force.
• Advantages: This setup provides a secure and reliable connection between the cog and the hub, designed to withstand the forces of fixed gear riding. It ensures proper chainline and durability.
• Components Needed:
  • New Rear Wheel or Hub: A wheel built around a fixed gear hub (often referred to as a "track hub" or "flip-flop hub" if it has threads for both fixed and freewheel on opposite sides).
  • Fixed Cog: Available in various tooth counts.
  • Fixed Gear Lockring: Crucial for security, must be compatible with the hub's threading.
  • Potentially a new chain: To achieve the correct length and optimal chainline.
• Chain Tensioning: If your frame has vertical dropouts, you'll need a mechanism to tension the chain, as the wheel cannot be moved fore and aft. This can involve an eccentric bottom bracket (EBB) or an eccentric rear hub, which are specialized components that allow for chain tension adjustment on frames not traditionally suited for fixed gear.

Essential Considerations for a Safe Conversion

Regardless of the method chosen, several critical factors must be addressed for a safe and functional fixed gear conversion:

• Chainline: This refers to the straightness of the chain between the front chainring and the rear cog. A perfectly straight chainline minimizes wear, reduces friction, and prevents the chain from derailing. Achieving this often requires careful selection of bottom bracket spindle length, chainring position, or rear hub spacing.
• Chain Tension: A fixed gear bike requires optimal chain tension—not too tight (which creates drag and wears components) and not too loose (which can cause the chain to skip or derail, leading to a sudden loss of control). Frames with horizontal dropouts allow easy tension adjustment by moving the wheel. Vertical dropout frames require an EBB or eccentric hub.
• Braking: While skilled fixed gear riders can slow down using leg resistance (skidding), this method is less efficient and can be dangerous, especially in emergencies or on descents. It is highly recommended, and in many places legally required, to install at least a front brake on a converted fixed gear bicycle. A rear brake provides additional safety. Never rely solely on leg braking, especially when starting out.
• Frame Compatibility: Frames with horizontal dropouts are ideal for fixed gear conversions as they allow for easy chain tension adjustment. Frames with vertical dropouts are more challenging and typically require an eccentric bottom bracket or hub to maintain proper chain tension, adding complexity and cost.
• Riding Style Adaptation: Riding fixed gear is a fundamentally different experience. There's no coasting, so your legs are always engaged. Learning to anticipate stops, manage speed, and brake effectively with your legs takes practice.

Pros and Cons of Riding Fixed Gear

Before undertaking a conversion, consider the implications for your riding experience:

Advantages:

• Direct Connection and Efficiency: Many riders appreciate the direct transfer of power and the feeling of being intimately connected to the bike.
• Simplicity and Low Maintenance: Fewer moving parts (no derailleurs, shifters, or freewheel mechanism) mean less to break and easier maintenance.
• Skill Development: Riding fixed gear can improve pedaling efficiency, cadence control, and bike handling skills.
• Lightweight: The minimalist setup often results in a lighter bike.

Disadvantages:

• No Coasting: Constant pedaling can be tiring, especially on long rides or descents.
• Braking Challenges: Relying solely on leg braking is less effective and potentially dangerous.
• Steep Learning Curve: Adapting to no coasting and different braking techniques takes time and practice.
• Lack of Gearing Options: Fixed gear bikes have only one gear ratio, which might be challenging on varied terrain.
• Increased Risk of Injury: If the chain breaks or the cog slips (especially with a "suicide hub"), you lose all means of propulsion and primary braking.

Conclusion: Is Conversion Right for You?

Converting a freewheel bike to a fixed gear is a project best approached with a clear understanding of the mechanical requirements and the unique demands of fixed gear riding. While a "suicide hub" offers a seemingly easy path, its inherent dangers make it an ill-advised choice. The safest and most reliable method involves investing in a dedicated fixed gear hub or wheel.

Ultimately, the decision to convert should be based on your mechanical aptitude, budget, and a genuine desire to experience the direct, minimalist ride of a fixed gear bicycle. Always prioritize safety by ensuring proper component selection, correct installation, and the use of adequate braking systems. When in doubt, consult with an experienced bike mechanic.