No ERG mode? How to use your gears as the resistance dial on a dumb trainer

ERG mode is the single feature people miss most when they ride without a smart trainer. You set an interval, the trainer holds the watts, and there is no negotiating with yourself — you either turn the pedals or you stop. It is genuinely excellent, and a wheel speed sensor cannot do it, because a sensor only counts revolutions and has no way to make your trainer do anything at all.

What you have instead is what every cyclist had until about 2015: a resistance dial made of gears, a clock, and your own judgement. It works. It requires more of you than ERG does, and slightly less of your wallet. Here is how to run a real session with it on a speed-sensor setup.

The basic idea

On a dumb trainer, the resistance you feel is set by two things: the trainer's own resistance curve — how hard it pushes back as the wheel spins faster — and the gear you have chosen. You cannot change the first mid-session, but you can change the second instantly, and that is enough.

A harder gear at the same cadence means a faster wheel, which means more resistance, which means more effort. So: shifting up is turning the dial up. One or two sprockets is a meaningful step; the big ring is a different world.

The trap is cadence. It is entirely possible to hold the same gear and halve your effort by dropping from 95 rpm to 70, and the screen will barely tell you. So pick a cadence you intend to hold, hold it, and change effort with the gear rather than by letting the legs slow down. If your sensor is a combined speed-and-cadence unit, you can see this on screen; if not, count for ten seconds and multiply by six.

Steering by heart rate

Without watts you need something that responds to effort rather than to equipment, and heart rate is it. Pair a chest strap — it connects over its own Bluetooth service, independently of the speed sensor, so you can have both.

Two things to know about using heart rate this way. It lags: after you shift up, it takes 30–60 seconds to arrive at the new effort, which makes it useless for intervals shorter than about two minutes. And it drifts: on a long steady effort it climbs a handful of beats across the session at identical effort, especially in a warm room, so do not chase a fixed number by easing off through the hour.

For anything under two minutes, judge by breathing and by how much you want it to stop. That is not a cop-out — rate of perceived exertion correlates extremely well with effort once you have a few weeks of practice at reading it.

Four sessions that work without power

All four are structured by time, which is the thing you can control exactly with no equipment at all. A clock is a more reliable instrument than a wattage estimate from an assumed resistance curve.

Making the trainer itself harder

If you run out of gears — and on a light setting you will, sooner than you expect — the trainer's own adjustment is the coarse control. On a magnetic trainer that is a lever or a remote with a few positions; on a fluid trainer, usually nothing, because the resistance curve is fixed by design; on rollers, nothing either, and that is rather the point of rollers.

Whatever you change, write it down, and change it as rarely as you can stand. The whole value of speed as a training number rests on the setup being identical between sessions — half a turn of a roller makes this week's numbers incomparable with last week's. Pick a setting that lets your hardest intervals feel hard in a gear you can still spin, then leave it alone for the block.

What will not carry over to your plan

One honest caveat. A ride with no power source carries no training load figure — no TSS — so an adaptive plan cannot reason about it. The ride saves, it appears on your calendar, it is a real session you really did. But the engine cannot see how hard it was, so it will not re-tune the week around it the way it does after a power ride.

If you are following a structured plan and this bothers you, that is the clearest signal that a power source is the next purchase — we wrote about when the upgrade is worth making. If you are riding to keep the engine turning through a wet month, it does not matter in the slightest, and the four sessions above will do the job perfectly well.