Guides
Turbo Trainer Resistance Levels Explained (2026 Guide)
The short answer
- Resistance is how a turbo trainer makes pedalling hard. The three mechanisms are magnetic, fluid and electronic (smart).
- Magnetic and fluid trainers have fixed or manually-set resistance: you change effort by shifting gears or turning a dial.
- Smart trainers add three software modes: manual level, ERG (the trainer holds a target wattage) and simulation (it mimics gradient).
- ERG mode is best for structured intervals; simulation is best for Zwift racing and group rides; manual is the safe fallback.
- More resistance is not better. What matters is whether the trainer can hold the wattage you actually train at, quietly and accurately.
Turbo trainer resistance is how the trainer makes your pedals hard to turn. It works in one of three ways: magnetic, fluid or electronic (smart). Basic magnetic and fluid trainers let you control effort yourself with your gears and sometimes a handlebar dial. Smart trainers control it automatically in software through three modes: manual level, ERG (it holds a set wattage) and simulation (it mimics a gradient). Get those modes straight and the rest of indoor training falls into place.
Most riders I coach arrive confused about “levels” when the real question is which control mode to use, so here is how I explain it to them from the first smart-trainer session onwards.
What “resistance” actually means on a turbo trainer
Resistance is the braking force the trainer applies to your rear wheel or cassette. The harder that brake works, the more watts you have to push to keep the same speed. Everything else, the modes, the dials, the app sliders, is just a different way of changing that braking force.
There are two layers to keep separate in your head:
- The mechanism: how the trainer physically creates resistance (magnetic, fluid or electronic).
- The control: how you change it (manual gears and dials, or smart software modes).
A cheap trainer has a basic mechanism and manual control. A premium smart trainer has an electronic mechanism and full software control. Most confusion comes from mixing these two layers up, so I will take them one at a time.
The three resistance mechanisms
Magnetic resistance
Magnetic trainers use magnets near a metal flywheel to create drag. Move the magnets closer and pedalling gets harder. They are cheap, light and usually let you set resistance with a handlebar lever across a few fixed steps. The downsides: the resistance can feel a bit “on or off” rather than progressive, and they get noisy and harsh at high speed.
This is the engine in budget wheel-on units like the one I cover in my BDBikes turbo trainer review and the Elite Novo Force. Perfectly fine for getting fit over winter if you accept the manual control and the noise.
Fluid resistance
Fluid trainers spin a paddle through a sealed chamber of viscous fluid. The faster you go, the more the fluid resists, so resistance builds progressively the harder you push, with no levels to set. That progressive curve feels far more like real road riding than magnetic, and fluid units are noticeably quieter. The catch is older designs could leak if overheated, though modern sealed units like the CycleOps Tempo Fluid are reliable. If quiet, road-like feel without electronics is your priority, fluid is the sweet spot.
Electronic (smart) resistance
Smart trainers use an electromagnetic brake controlled by software. An app can change the resistance hundreds of times a second, which is what drives ERG and simulation modes. This is the mechanism in every direct-drive unit I rate highly, from the Tacx Flux 2 up to the premium picks in my best direct drive turbo trainers guide. It is the only mechanism that can read your power and actively hold a target.
| Mechanism | How you control it | Ride feel | Noise | Typical price |
|---|---|---|---|---|
| Magnetic | Manual: gears + handlebar dial | Stepped, can feel harsh | Loud at speed | £ |
| Fluid | Manual: gears only (progressive) | Smooth, road-like | Quiet | ££ |
| Electronic (smart) | App-controlled: ERG / SIM / level | Most realistic, dynamic | Very quiet (direct drive) | £££ to ££££ |
Manual levels vs ERG vs simulation
This is the part that trips up most newcomers, so here is the plain-English version of each smart-trainer mode. Basic trainers only ever have the first one.
Manual / level mode
You pick a fixed resistance level, say level 5 of 10, and the trainer holds that braking force steady. Your effort then changes with your gears and cadence, exactly like riding outside on a road with constant drag. Every trainer can do this, smart or not. On a smart trainer it is the mode I fall back to when an app crashes or I just want a no-thinking-required spin. It is also the only mode a magnetic or fluid trainer offers, with the “level” being whatever your dial or gear choice gives you.
ERG mode (the trainer holds a wattage)
In ERG mode you set a target, for example 220 W, and the smart trainer constantly adjusts its electromagnetic brake so you stay at 220 W regardless of gear or cadence. Slow your legs down and it gets harder, spin faster and it eases off. It is brilliant for structured intervals because you cannot cheat: the workout makes you hit the number. A good unit settles onto the target smoothly and holds it within a percent or two of where you set it, so the effort stays honest. A poor one overshoots and hunts around the figure, which you feel as the resistance surging and fading under your legs.
Simulation (SIM) mode
In simulation mode the trainer matches the gradient of a virtual course. Hit a 6% climb in Zwift and the resistance ramps up so it genuinely feels like a climb, then a descent goes light and fast. Here your gears matter again, just like outdoors: you shift to spin up climbs and push a big gear on the flat. SIM mode is what makes Zwift racing and group rides feel alive, and it is the mode I use for anything that is not a fixed-wattage workout. Apps usually let you scale the gradient (trainer difficulty), so you can soften a brutal Alpe climb to something your gearing can handle.
How to choose the right mode for a session
Use this quick decision order. It is what I tell every rider I coach when they get their first smart trainer.
- Structured intervals or a fixed plan (threshold blocks, sweet spot, VO2 efforts): use ERG mode and let the trainer do the thinking.
- Racing, group rides or free exploring in Zwift or MyWhoosh: use simulation mode so climbs and descents feel real.
- App problems, a quick warm-up, or you just want to ride without numbers: use manual level mode.
If you are weighing up the underlying hardware rather than the software, my direct drive vs wheel-on comparison goes deeper on which mechanism suits which rider.
Does maximum resistance matter?
Manufacturers love to quote big headline figures: a 1500 W or 2000 W ceiling, or a simulated gradient like 16% or 20%. In practice almost no club rider ever bumps into those limits. I have never once maxed out a mid-range smart trainer in normal training, and I push 300 W intervals regularly.
The exception: very strong sprinters and anyone who simulates extreme climbs at low cadence will appreciate a higher ceiling and a heavier flywheel. For everyone else, spend the money on accuracy and quietness instead. If accuracy is your concern, I cover how to read and trust the numbers in my guide on understanding power readings on your turbo trainer.
My verdict as a coach
Stop thinking about resistance “levels” and start thinking about modes. Magnetic and fluid riders use their gears and dial as the resistance, and that is genuinely all you need to get fit. If you have a smart trainer, ERG mode for workouts and simulation for racing will transform your indoor training far more than any headline wattage figure ever will. Buy for accuracy and quiet, train with the right mode, and the resistance looks after itself.