Virtual shifting vs ERG vs SIM mode, explained
By mattapps · Published 12 October 2026 · Last checked 12 October 2026
ERG mode makes a smart trainer hold a target power, whatever your cadence. SIM mode makes trainer resistance follow the virtual gradient of the road. Virtual shifting changes the simulated gear ratio, so the same effort produces a different cadence and speed. Shifting matters most in SIM mode, because in ERG the target power wins.
What is ERG mode?
ERG mode is a trainer mode where the smart trainer holds a fixed target power. You pedal faster and the trainer makes it harder. You pedal slower and it makes it easier. The watts stay where the workout asked for them.
That is why ERG is popular for structured intervals. A workout says "250 watts for five minutes" and the trainer enforces it. You do not need to shift or think about gearing. Your cadence is free to change, but your power is not.
The catch is that it can feel rigid. If you fall behind the target, the resistance does not back off. Some riders find that hard to recover from at the end of a long interval.
What is SIM mode (resistance mode)?
SIM mode, often called resistance or gradient mode, makes the trainer feel like the virtual road. When the game shows a climb, the trainer adds resistance. On a descent, it eases off. Your power is whatever you produce against that resistance.
Nothing here fixes a target. If you pedal harder, you go faster and the watts rise. That makes SIM mode the natural fit for free rides and races, where you decide how hard to go.
The gradient is the main input. A steeper slope in the game means more load at the same speed. Rider weight, drafting and other game physics also play a part, but the gradient is the easiest piece to feel.
What does virtual shifting do?
Virtual shifting changes the gear ratio that the game simulates. A trainer has no real chain to move, so the software pretends. Shifting to an easier virtual gear lets you spin at a comfortable cadence on a climb. A harder gear gives you more speed for the same cadence.
In practice, it changes how cadence, speed and effort relate to one another. An easier gear means you spin faster for a given speed. A harder gear means you push a bigger gear more slowly. That is why a shift can feel like a change in how the trainer responds.
Games implement this differently. As one example, MyWhoosh calls its version MyShift, with 30 virtual gears and a ride that starts in gear 15. We cover it in MyShift explained.
How do the three compare side by side?
They answer three different questions: what power should I hold, what does the road feel like, and what gear am I in. The table sets them next to each other.
| ERG mode | SIM / resistance mode | Virtual shifting | |
|---|---|---|---|
| What it controls | Power at the trainer | Resistance from the virtual gradient | Simulated gear ratio |
| What stays fixed | Target power | Nothing. You choose the effort | Nothing. You choose the gear |
| Effect of cadence | Power does not change | Cadence and gear set your speed and power | Changes how cadence maps to speed |
| Typical use | Structured workout intervals | Free rides, races, climbs | Staying at a comfortable cadence on varied terrain |
| Do you shift? | Usually no | Often yes | That is the action itself |
Can virtual shifting and ERG mode run together?
Usually not in a meaningful way. In ERG mode the trainer holds a target power, so changing the virtual gear does not change your watts. It mostly changes the cadence you need to hit that power, if the platform allows it at all.
Virtual shifting makes more sense in SIM mode, where gear choice affects how a given effort turns into speed and cadence. How a specific app handles each mode is a software decision, so check that app's own settings.
Which mode should you use for which ride?
Use ERG for a workout with set targets, and SIM mode for riding a route or racing. Virtual shifting only matters when the ride uses gears.
- Interval workout with a target power: ERG mode. Let the trainer set the load and focus on the effort.
- Free ride or race on a route: SIM mode, with virtual shifting to keep cadence comfortable on climbs and flats.
- Easy recovery spin: either. SIM mode is more natural, ERG at a low target keeps you from drifting too hard.
Whichever you choose, the smart trainer and the app do the work. If you are changing gears from a phone, read how to shift gears in MyWhoosh from an Android phone.
Does a phone keyboard app do any of this?
No. A phone keyboard app sends keystrokes to your computer and stops there. It cannot set a target power, pick a trainer mode or see what your trainer is doing.
GearPad, our own app, works that way. It acts as a Bluetooth keyboard and presses the shift keys that a game such as MyWhoosh already listens for. ERG, SIM mode and the trainer connection stay in the game and with your smart trainer. If you are weighing ways to send shift commands at all, see Zwift Click alternatives.
Quick answers
Does a steeper gradient always mean harder pedaling?
In SIM mode, a steeper gradient raises the resistance you feel at a given speed. Your gear and speed still shape the exact effort.
Do I need a smart trainer for these modes?
ERG and SIM mode both depend on a trainer that can be controlled by an app, which is what a smart trainer is. Virtual shifting is a software feature, so what it needs depends on the app.
Why does my cadence change when I shift?
A different virtual gear ratio changes the speed you get from each pedal stroke. To keep the same speed, you pedal faster in an easier gear and slower in a harder one.
