Oval Chainring

Summary

An oval chainring is a non-circular chainring designed to smooth out pedaling dynamics by varying the gear ratio through the crank’s rotation. The goal is to improve efficiency, reduce knee strain, and optimize power delivery by matching mechanical advantage to the natural strengths and weaknesses of the rider’s pedal stroke.

Key Facts

  • Introduced: Concept dates back to the late 19th century; modern iterations gained popularity in the 1980s and again in the 2010s
  • Category: Component
  • Also known as: Elliptical chainring, non-round chainring
  • Used by: Road cyclists, mountain bikers, triathletes
  • Popularized by: Rotor, Osymetric, AbsoluteBLACK, Shimano Biopace (historical)
  • Compatibility: Most modern cranksets (with model-specific spider interfaces)
  • Official website(s): https://absoluteblack.cc, https://rotorbike.com

Overview

The oval chainring is one of cycling’s more polarizing innovations—not because it doesn’t work, but because it challenges the visual and mechanical norm of the bicycle drivetrain. Instead of a traditional round shape, an oval chainring features a carefully engineered elliptical profile. This causes the effective gear ratio to change as the cranks rotate, theoretically optimizing torque where a rider is strongest and minimizing resistance where the rider is weakest.

While early non-round rings appeared in the 1890s, the concept first gained widespread attention in the 1980s with Shimano’s Biopace system. Designed to reduce the “dead spots” in the pedal stroke, Biopace introduced non-circular chainrings to the masses. The problem? Its orientation and execution led to an awkward ride feel and unclear benefits, resulting in a widespread retreat back to round rings.

It wasn’t until the 2000s and 2010s—driven by brands like Rotor, Osymetric, and AbsoluteBLACK—that oval chainrings returned in a refined form. With better biomechanical understanding, CAD design, and modern rider feedback, these newer designs positioned the “long axis” of the oval to match the power phase of the stroke (the downstroke), offering more natural pedaling dynamics.

Today, oval rings are used across disciplines. Mountain bikers appreciate their climbing traction and low-cadence smoothness. Time trialists and triathletes favor their efficiency at steady-state power. Some riders even report knee relief or better cadence stability. However, oval rings still require personal adaptation, and not every rider perceives the benefits equally.

How It Works

At the heart of the oval chainring concept is biomechanical optimization. During a typical pedal stroke, a rider’s power output is not constant. Most of the usable force comes during the downstroke (typically from 1 o’clock to 5 o’clock), while the top and bottom of the stroke—the so-called “dead spots”—offer little mechanical leverage.

An oval chainring alters the effective gear ratio depending on crank position. It does this by changing the radius between the crank spindle and the chain contact point:

  • In the power phase (downstroke), the chainring presents its larger diameter. This increases resistance slightly but allows the rider to push a larger gear where they are strongest.
  • In the weaker parts of the stroke (around top and bottom dead center), the ring becomes “smaller.” This decreases resistance and helps the crank move through the low-torque portions more easily.

The result is a smoothed-out pedal stroke. Riders often describe it as feeling more circular than a round ring, with less variation in perceived resistance.

Key Engineering Considerations

  • Orientation: The “clocking” of the oval—i.e., where the long and short axes fall in relation to the crankarm—is critical. Modern oval rings place the long axis in the power zone for maximum effectiveness.
  • Ovality Percentage: The degree to which a ring is oval (e.g., 10% vs 12% ovality) affects how pronounced the effect is. Higher ovality increases the variance in effective gearing throughout the stroke.
  • Chain Retention: Many oval rings use narrow-wide tooth profiles for 1x drivetrains to ensure secure chain retention, even as the chainline subtly shifts through the rotation.
  • Front Shifting (2x Systems): Oval rings can make front shifting less precise due to changing tooth profiles. For this reason, oval rings are most commonly found on 1x systems.

Performance Debate & Use Cases

Despite their mechanical logic, oval chainrings remain controversial in some circles—not because they don’t work, but because not every rider perceives the benefits in the same way.

Claimed Benefits

  • Smoother Torque Application: Reduces the feeling of “pulsing” resistance, especially at lower cadences.
  • Improved Traction: In technical climbs, particularly off-road, oval rings help reduce torque spikes that can cause wheel spin.
  • Efficiency Gains: Some lab tests (and plenty of anecdotal accounts) suggest that ovals reduce oxygen consumption or muscular fatigue over long distances.
  • Knee Relief: Riders with knee sensitivities often report reduced strain due to more consistent resistance.

Common Criticisms

  • Adaptation Period: It can take several rides for legs to adjust to the new feel—especially in high-cadence or sprinting efforts.
  • Front Shifting Issues: On 2x setups, oval chainrings can complicate front shifting due to non-uniform ring profiles.
  • Marginal Gains: While some riders report benefits, others see little difference in power output, cadence stability, or ride feel.

Ideal Users

  • Mountain bikers riding technical climbs
  • Riders with 1x drivetrains seeking chain control and torque smoothing
  • Time trialists and triathletes focused on seated, consistent power
  • Riders with joint sensitivity or cadence control issues

Notable Implementations

  • AbsoluteBLACK Oval Rings – Widely used in MTB and road 1x drivetrains; known for high-quality machining and clean aesthetics.
  • Rotor Q-Rings – Used in road, track, and triathlon; often adjustable in clocking for fine-tuned optimization.
  • Osymetric Chainrings – High-ovality rings seen in use by riders like Bradley Wiggins and Chris Froome during Tour de France efforts.
  • Garbaruk Oval Rings – Lightweight CNC oval rings popular in XC and trail applications.
  • Shimano Biopace (1980s–90s) – Early commercial oval system; now considered an example of poor orientation and execution.

Related Terms

References

  • Rotor: Q-Ring Technology White Paper
  • AbsoluteBLACK: Oval Ring Biomechanics Explained
  • Journal of Sports Sciences: Torque Profile Alterations with Oval Rings
  • Cycling Weekly: Oval Chainring Testing and Pro Usage
  • Pinkbike: Long-Term Review of Oval Rings in MTB
  • Sheldon Brown: Historical Overview of Biopace Chainrings
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