ERG mode is one of the most powerful tools in your indoor training arsenal. It's also one of the most misused. If you've ever found yourself in a death spiral — cadence dropping, resistance climbing, legs screaming — you've experienced what happens when ERG mode works against you instead of for you.

Here's what's actually happening, and how to use ERG mode the way it was designed.

What ERG Mode Actually Does

When you enable ERG mode, your smart trainer takes over resistance control. Instead of selecting a gear and pedaling against a fixed resistance, the trainer adjusts resistance in real time to hit a target power number — regardless of your cadence.

The key word: regardless of cadence.

This is where most riders get into trouble.

The Death Spiral Explained

You're doing a threshold interval at 280 watts. Your cadence slips slightly — fatigue, a moment of distraction. The trainer responds by increasing resistance to maintain the target wattage. Your legs feel heavier, so cadence drops further. The trainer increases resistance again. Repeat until you stop pedaling.

This isn't a bug. It's physics.

The fix isn't to fight the resistance. In ERG mode, cadence is the variable you control — power is the output, not the input. Drop your cadence, you're fighting more resistance. Maintain your cadence, the trainer does the heavy lifting.

Cadence: Your Primary Lever

Most experienced ERG mode riders settle on a cadence range and stay there. 85–95 RPM is common for threshold and VO2 work. For lower-intensity efforts, you might drop to 75–80. The exact number matters less than consistency.

Pick a number. Commit to it. When a hard interval starts, focus entirely on spinning that number — not on the power display. The watts will follow.

This is a fundamentally different mental model from outdoor riding. Outdoors, you feel the terrain and adjust. Indoors, you create the conditions by controlling cadence.

Gear Selection Still Matters

Many cyclists think ERG mode makes gear selection irrelevant. It doesn't.

Your smart trainer has a response time. A bigger flywheel effect — achieved by using a harder gear, bigger chainring and smaller cassette cog — makes the trainer feel smoother and more road-like. It also makes ERG response less twitchy.

For hard efforts (VO2max intervals, threshold work), use a bigger gear. Your flywheel inertia acts as a buffer against sudden resistance swings. For endurance rides at low power, smaller gears are fine.

The practical recommendation: big ring, middle cog. This gives you enough flywheel momentum without cross-chaining.

The Ramp-Up Period

When an interval starts, ERG mode doesn't instantly jump to target power. The trainer ramps resistance over 5–10 seconds, depending on the model.

Don't start sprinting when the interval hits. Start pedaling at your target cadence before the interval begins, then let the trainer find the resistance. Maintain cadence through the ramp-up.

The same logic applies at interval endings. When resistance drops, keep pedaling smoothly through the transition. Sudden cadence changes during transitions produce noisy power data and make the next effort harder to start cleanly.

When to Turn ERG Off

ERG mode isn't the right tool for every session.

Sprint work, race simulations, group rides — these require you to control resistance yourself. ERG mode imposes structure that kills the spontaneity of maximal sprints or dynamic pacing. Switch to resistance or slope mode for anything involving all-out efforts or variable power.

For structured training with defined power targets — intervals, pyramids, sweetspot work — ERG mode is unbeatable. For free riding, turn it off.

VeloWorkout lets you switch between modes mid-ride, so you're not locked into a single approach for an entire session. A common setup: ERG mode for warm-up and structured intervals, then resistance mode for any sprint work at the end.

Calibration: The Step Nobody Skips Twice

Smart trainer power accuracy degrades without regular calibration. Temperature, tyre pressure (on wheel-on trainers), and mechanical wear all shift the baseline reading.

Calibrate before your first serious session of the week. Most trainers require a 10-minute warmup before calibration produces accurate results. After that, your power numbers mean something — especially critical if you're tracking FTP progression over months.

The riders who complain that their FTP "randomly dropped" are usually the ones who skipped calibration after the trainer sat cold in the garage for two weeks.

The Consistency Test

Here's a simple drill to check whether your ERG setup is dialed in:

Do a 10-minute steady-state effort at threshold power. Watch your cadence — not your power. If power varies by more than ±5 watts while cadence stays constant, either calibration is off, there's a mechanical issue with the trainer, or (on wheel-on trainers) tyre pressure needs adjusting.

If you can hold cadence steady and power follows smoothly, your setup is dialed. Now you can trust the data you're generating — and consistent, trustworthy data is what separates structured indoor training from just sweating in your garage.

ERG mode mastered is ERG mode transparent. You stop thinking about resistance and start thinking about execution. That's when indoor training actually starts working.