Smart Trainers: Understanding Coasting and Its Training Implications

Can you coast on a smart trainer?

While you can physically stop pedaling on a smart trainer, the experience is fundamentally different from "coasting" outdoors. Due to the absence of external forces like gravity and significant wind resistance, the momentum generated by the flywheel dissipates rapidly, leading to a quick stop rather than sustained movement.

The Concept of Coasting in Cycling

In outdoor cycling, "coasting" refers to the act of ceasing to pedal while the bicycle continues to move forward, propelled by momentum, gravity (on downhills), or a combination of both. This allows for brief periods of rest, tactical positioning within a group, or simply enjoying a downhill descent without expending energy. The bicycle's speed is maintained by the inertia of the rider and bike, overcoming rolling resistance and air resistance until these forces eventually bring it to a halt if no further propulsion is applied.

How Smart Trainers Simulate Riding

Smart trainers operate by holding the rear wheel (wheel-on trainers) or directly engaging the drivetrain (direct-drive trainers) and applying a controlled resistance. This resistance can be adjusted by software to simulate various gradients (slopes), wind resistance, or to maintain a specific power output (ERG mode). Key components include:

• Flywheel: A heavy disk that provides inertia, mimicking the momentum of a rider on a real bike.
• Resistance Unit: An electromagnetic or fluid-based system that applies braking force to the flywheel or directly to the drivetrain.
• Freewheel Mechanism: Similar to a bicycle's rear hub, this allows the cassette to spin independently of the pedals when you stop pedaling.

Technical Considerations: Flywheel and Resistance

When you stop pedaling on a smart trainer, the freewheel mechanism allows the cassette and flywheel to continue spinning. However, the forces at play are vastly different from outdoor riding:

• Resistance Application: The trainer's resistance unit is constantly applying a programmed load. Unlike outdoors where forward momentum can overcome air and rolling resistance for a period, the trainer's resistance is designed to simulate continuous effort or a specific power target.
• Flywheel Inertia: While the flywheel provides some inertia, it's typically much less than the combined inertia of a rider and bicycle moving at speed outdoors. This limited inertia, coupled with the constant resistance from the trainer, means that once pedaling stops, the flywheel's rotation slows down very quickly.

The Physics of "Coasting" Indoors vs. Outdoors

The primary reason "coasting" on a smart trainer differs so significantly from outdoor cycling lies in the fundamental physics involved:

• Outdoor Cycling:
  • Gravity: On a downhill, gravity actively pulls the rider and bike forward, generating speed without pedaling.
  • Air Resistance: While a resistive force, it's the primary factor limiting top speed and is overcome by momentum.
  • Rolling Resistance: Friction between tires and the road, a relatively minor resistive force.
  • Significant Mass: The combined mass of rider and bike provides substantial momentum.
• Smart Trainer Cycling:
  • No Gravity: The trainer is on a flat surface; there is no gravitational pull assisting forward motion.
  • No Wind Resistance: There's no actual air resistance to overcome. The trainer simulates it through increased resistance, but it doesn't provide the "push" of wind behind you.
  • Controlled Resistance: The trainer's unit is actively applying resistance, even if you stop pedaling, to simulate the road feel or a specific workout. This acts as a constant brake.
  • Limited Inertia: The flywheel's inertia is designed to create a smooth pedaling feel, not to sustain motion for extended periods without power input against a constant resistance.

When you stop pedaling on a smart trainer, the flywheel's momentum quickly dissipates against the trainer's internal resistance, bringing the system to a near-immediate halt.

Training Implications of Coasting (or lack thereof)

The inability to truly "coast" has significant implications for indoor training:

• Continuous Effort: Indoor cycling typically demands more continuous power output. Without opportunities to coast, your legs are almost constantly engaged, leading to a higher average power for a given duration compared to a similar outdoor ride.
• Reduced Recovery: The lack of coasting means fewer opportunities for active or passive recovery during a ride. This can make indoor workouts feel more demanding, especially for longer durations or interval sessions.
• Specific Adaptation: This continuous effort is excellent for building aerobic capacity and muscular endurance, as it keeps your heart rate and power output consistently elevated.
• Pacing Differences: Riders accustomed to outdoor pacing, which includes coasting sections, may find indoor rides require a different pacing strategy to manage fatigue.

When "Coasting" Might Still Occur (and why)

While true coasting is largely absent, there are specific scenarios where the trainer's behavior might resemble it:

• Virtual Downhills: In virtual cycling platforms like Zwift or Rouvy, when you encounter a downhill section, the smart trainer will significantly reduce its resistance. This allows you to spin the pedals with very little effort, or even stop pedaling, and still maintain a virtual speed. However, this is the trainer reducing resistance, not you gaining "free" momentum from gravity. The flywheel will still decelerate quickly if you fully stop pedaling, though more slowly than on a flat or uphill.
• Between Intervals: During structured workouts, there might be very low-power recovery intervals or complete rest periods where the trainer drops resistance to near zero. In these moments, you can stop pedaling, and the flywheel will take slightly longer to stop, but it will still stop due to residual friction and the absence of any propulsive force.

Conclusion

In essence, while you can physically cease pedaling on a smart trainer, the experience is not akin to outdoor coasting. The smart trainer's design, which lacks the external forces of gravity and significant air resistance, coupled with its active resistance unit, causes any momentum to dissipate rapidly. This fundamental difference means indoor training demands a more continuous effort, offering fewer opportunities for passive recovery but providing an excellent environment for focused, high-intensity, and highly controlled training. Understanding this distinction is key to optimizing your indoor cycling workouts and appreciating the unique demands of the virtual road.