Quick Answer: Pedal assist (PAS) is the electric bike feature that boosts your own pedaling power rather than replacing it — a sensor detects that you’re pedaling and the motor adds a proportional amount of extra power, stopping the moment you stop pedaling. Most bikes offer multiple assist levels (commonly 5, or named modes like Eco/Tour/Sport/Turbo on premium systems), and the type of sensor used — cadence or torque — changes how natural that power feels far more than the number of levels does. This guide breaks down how each sensor type works, what each level actually changes, and how pedal assist differs from a throttle.
Pedal assist by the numbers
- A torque sensor samples pedaling force up to roughly 1,000 times per second, compared with just a handful of readings per wheel revolution on a typical cadence sensor — the main reason torque-sensor bikes feel smoother and more responsive underfoot, per Electrek’s torque-vs-cadence sensor breakdown.
- On Bosch’s classic four-mode system, each level applies a fixed power multiplier on top of your own effort: Eco adds about 60%, Tour about 140%, Sport about 240%, and Turbo up to 340% — meaning Turbo can draw several times the battery of Eco over the same ride.
- Class 1 e-bikes cap pedal-assist speed at 20 mph; Class 3 e-bikes cap it at 28 mph, per the 3-class system most US states have adopted, and neither class lets the motor do anything once you stop pedaling.
- The CPSC caps low-speed electric bicycle motors at 750W (15 USC §2085) — pedal assist levels change how much of that power is applied and when, not the bike’s legal power ceiling.
How pedal assist actually works
Every pedal-assist e-bike has a sensor near the bottom bracket (or built into the rear hub) that tells the motor’s controller whether — and on better bikes, how hard — you’re pedaling. The controller then adds a proportional amount of extra power from the battery through the motor. Lift your feet off the pedals, coast, or stop, and the assist cuts out almost immediately; this is the legal and mechanical line that separates pedal assist from a throttle, which can move the bike with zero pedaling input, the way a moped or scooter does. Many bikes — most Class 2 models in particular — offer both a throttle and pedal assist on the same machine, letting you choose per ride or even per hill.
Cadence sensor vs. torque sensor
| Cadence sensor | Torque sensor | |
|---|---|---|
| What it measures | That the pedals are turning | How hard you’re pressing the pedals |
| Sample rate | A few readings per wheel revolution | Up to ~1,000 times per second |
| Feel | On/off, slight lag, “zippy” | Smooth, builds with your effort |
| Typical cost | Lower — most budget hub-motor bikes | Higher — common on Aventon, Velotric, mid-drive bikes |
| Best for | Casual riders, lowest price point | Riders who want a natural, bike-like feel |
Neither sensor type is “wrong” — cadence sensors are simpler, cheaper, and perfectly functional, which is why they remain the default on most sub-$1,500 hub-motor bikes. Torque sensors cost more to manufacture but reward hillier terrain and longer rides with power that matches what your legs are actually doing, which is why they’ve become a selling point on mid-tier and premium bikes alike — see how it plays out model-by-model in our best electric bike rankings.
What each assist level changes
| Level (cadence-sensor system) | Typical use | Effect on range |
|---|---|---|
| 0 | No assist — pedal like a normal bike | Longest (battery untouched) |
| 1-2 | Flat ground, light headwind, conserving battery | Long |
| 3 | General all-purpose riding | Moderate |
| 4 | Hills, cargo, headwinds | Shorter |
| 5 (max) | Steep climbs, heavy loads, quick acceleration | Shortest |
Named-mode systems like Bosch’s Eco/Tour/Sport/Turbo work on the same principle with fixed support multipliers instead of numbered steps (see the stats above), and newer dynamic modes — like Bosch’s Tour+ — adjust the multiplier automatically based on how hard you’re already pushing, rather than locking you to one fixed percentage. Either way, the pattern holds across every brand: the lowest level preserves range, the highest sacrifices range for power, and most riders spend the bulk of a ride somewhere in the middle.
See which sensor type and level range are on our top-rated bikes
- Torque-sensor picks ride smoother on hills and long commutes.
- Cadence-sensor picks cost less and are simpler to maintain.
- Every pick below lists its assist levels and claimed range.
Ordering a bike or accessories online means you’re relying on the carrier’s delivery window more than usual for something this size — a free Audible trial is a reasonable way to pass a long commute once the bike arrives, assist level and all (sponsored link; we may earn a fee if you sign up, at no extra cost to you).
Pedal assist and the class system
The number of assist levels a bike has is a separate question from which class it’s legally sold as. A Class 1 e-bike provides pedal assist only, up to 20 mph; a Class 3 e-bike provides pedal assist up to 28 mph; a Class 2 e-bike adds a throttle capped at 20 mph on top of whatever pedal-assist levels it offers. None of that changes how many assist levels a given bike has — a Class 1 bike can still have 5 levels or 4 named modes, it just stops boosting your speed at 20 mph regardless of which one you pick. Our Class 1 vs Class 3 e-bike guide covers the full legal breakdown state by state.
The bottom line
Pedal assist is what makes an e-bike feel like a bike rather than a scooter: the motor only ever adds to what your legs are already doing, and it stops the instant you do. The sensor type — cadence or torque — changes how natural that power feels far more than the number of levels does, and the level you choose on a given ride is simply a trade between speed/effort and range. If you’re choosing a first e-bike, start with our best electric bike for beginners guide, which leans toward smoother torque-sensor options for exactly this reason, or see our full best electric bike rankings for picks across every budget and sensor type.