ERG mode explained: when to use it, when to turn it off

ERG mode is the feature that turned smart trainers from expensive resistance units into genuine training tools. The idea is simple: you tell the trainer what wattage you want, and it applies exactly the resistance needed to keep you there — regardless of what gear you're in or how fast you're pedalling. Shift up, shift down, speed up, slow down: the number on the screen stays put.

It's brilliant, and it isn't always the right tool. Here's how it works and when to switch it off.

How it actually works

Power is force multiplied by speed. Your trainer measures how fast the flywheel is spinning and adjusts its electromagnetic brake to make up the difference. Pedal faster and it eases off; pedal slower and it clamps down harder. The result is that your gearing becomes irrelevant — you can do an entire interval session in one gear without touching the shifters.

The trade-off is a slight lag. The trainer has to notice a change and respond, which usually takes a second or two. For a 12-minute sweet-spot block that's invisible. For a 10-second sprint it's the whole effort.

When to use it

When to turn it off

The alternative is usually called slope mode (or SIM mode). There, the trainer simulates a gradient and your power is whatever you produce against it — exactly like the road. Gears matter again, and so does pacing.

The spiral of death

Every ERG user meets this eventually. You're deep into a hard interval, your cadence starts to fall, the trainer adds resistance to maintain the target, which makes your cadence fall further, which adds more resistance — and within about five seconds you're at 45 rpm, grinding, and about to come to a complete stop.

It isn't a fault. It's the logic of ERG taken to its conclusion. Here's how to avoid it:

A word on 'ERG makes you soft'

There's a persistent argument that ERG mode weakens you as a rider because it removes the need to self-regulate. There's a grain of truth in it: pacing is a skill, and skills atrophy when a machine does them for you. A rider who only ever trains in ERG can be genuinely poor at judging a 20-minute effort on a real climb.

But the answer isn't to abandon ERG — it's to ride some sessions without it on purpose. Do your long steady blocks in ERG, where consistency is the whole point. Then do your race simulations, your climbs and your sprints in slope mode, pacing them yourself. You get the precision and keep the skill. (Our guide to pacing a climb with power covers the skill side.)

Getting it set up

ERG needs a trainer with controllable resistance — which in practice means anything sold as a "smart trainer" in the last decade, speaking the FTMS standard over Bluetooth. If you're still shopping, our smart trainer buying guide covers what to look for.

After that, any modern app can drive it. In Moveee Indoor you pick a structured workout, pair the trainer over Bluetooth in your browser, and it holds each interval's target watts for you automatically — while you ride one of your own real routes rendered in 3D from map data. Outside a workout it switches to gradient-driven resistance instead, so when the road climbs, so does the effort. It's free while in alpha and there's nothing to install.

Use ERG for the work that needs precision. Turn it off for the work that needs feel. That's the whole rule.