Smart Trainers Explained: Types, ERG Mode and What to Look For

A smart trainer is an indoor bike trainer that measures your power and can change its resistance on command from an app. That second part is what makes structured workouts and virtual rides possible: the app tells the trainer how hard to push back, and the trainer reports your watts, cadence and speed. We do not review or rank specific models; this guide explains how the types and features differ so you can judge any trainer you look at.

Smart trainer types

Type	How it works	Pros	Cons
Wheel-on	Rear tire presses on a roller	Cheaper, quick to fit	Tire wear, slip, less accurate, louder
Direct drive	Rear wheel off, bike mounts on the trainer's cassette	Accurate, quiet, realistic feel, high resistance	Pricier, heavier, cassette compatibility
Smart bike	A complete stationary bike with built-in resistance	No bike swapping, adjustable fit, shared use	Most expensive, takes permanent space

For most riders who train regularly indoors, direct drive is the usual choice.

ERG mode vs simulation mode

• ERG mode holds a target power. If the workout asks for 250 W, the trainer adjusts resistance so you produce 250 W whatever your gear or cadence. It is ideal for structured workouts.
• Simulation (SIM) mode mimics gradient, wind and rolling resistance in virtual worlds: hills get harder, descents easier, and you shift gears like outdoors.
• Resistance or level mode sets a fixed resistance, useful for self-paced efforts such as a 20-minute FTP test.

Specs that matter

• Power accuracy: usually given as ±1% to ±3%. Tighter is better for consistent training data.
• Maximum power and gradient: matters mostly for strong sprinters and steep virtual climbs.
• Connectivity: ANT+ FE-C and Bluetooth FTMS are the standard control protocols; most apps support both.
• Flywheel and ride feel: heavier or simulated flywheels feel smoother, more like the road.
• Noise: direct-drive trainers are much quieter than wheel-on ones; drivetrain noise remains.
• Bike compatibility: axle standards (quick release, thru-axle) and cassette type.
• Calibration: some trainers need a spin-down; others calibrate automatically.
• Footprint and folding if space is tight.

Setting one up

1. Mount the bike and check the cassette and axle fit.
2. Update the trainer's firmware in its companion app.
3. Pair it with your training app, for example Zwift or TrainerRoad.
4. Run a calibration if required.
5. Set your FTP and load a workout. Our guides for Zwift and TrainerRoad show how to add custom workouts.