A flat Sydney commute at 25 km/h needs roughly 170 watts at the rear wheel, or about 213 watts drawn from the battery once you allow for motor and controller losses. That is the honest answer to the e-bike watts question: the number on the motor sticker is a limit, not a requirement. Most riding sits far below it, and the moment a hill appears the demand can jump four-fold.
At Cyberbikes in Leichhardt we get asked for “more watts” almost every week. Nearly always, what the rider wants is a motor that holds power on a climb without fading, and a battery big enough that the climb does not matter. Those are different problems — and here is what the physics, and Grin Technologies’ engineering pages, say about both.
How many e-bike watts does it take to hold 25 km/h?
Three forces take power away from you: rolling resistance, air drag and gravity. Rolling resistance grows in a straight line with speed. Air drag grows with the square of speed, so the power it eats grows with the cube. Gravity only shows up when the road tilts, and then it dominates everything.
The table below is our own calculation using the standard road-load equation for a 110 kg system (a 37 kg cargo-class e-bike plus a 73 kg rider and a bag), a rolling resistance coefficient of 0.008, a frontal drag area of 0.55 m², still air at 1.2 kg/m³, and a combined motor-and-controller efficiency of 80%. Change the rider, the tyres or the wind and the numbers move — you can run your own version in Grin’s motor simulator at ebikes.ca.
| Riding condition | Power at the wheel | Drawn from battery | Energy use |
|---|---|---|---|
| 15 km/h, flat | 60 W | 75 W | 5.0 Wh/km |
| 20 km/h, flat | 105 W | 131 W | 6.5 Wh/km |
| 25 km/h, flat | 170 W | 213 W | 8.5 Wh/km |
| 3% grade at 15 km/h | 195 W | 243 W | 16.2 Wh/km |
| 6% grade at 25 km/h | 619 W | 774 W | 31.0 Wh/km |
| 10% grade at 15 km/h | 507 W | 634 W | 42.3 Wh/km |
Read the first three rows again. Going from 20 km/h to 25 km/h raises battery draw from 131 W to 213 W — a 63% increase for 5 km/h — because air drag at the wheel nearly doubles, from 57 W to 111 W. Speed is expensive, and that is why two riders on identical bikes get wildly different ranges.
Why does a hill multiply the watts you need?
Because gravity does not care how fast you are going — it charges you by how much mass you lift per second. On a 6% grade at 25 km/h, the climbing term alone is 449 W at the wheel. Add rolling and air drag and you are asking for 619 W at the wheel, or about 774 W from the battery. That is roughly 3.6 times the demand of the same speed on the flat.
Sydney is full of grades like that. The back streets of Balmain and Annandale are short, but steep enough to triple what your motor is asked for.
This is also where the sticker number stops meaning much. Grin Technologies, who build and test motors for a living, put it bluntly on their power ratings page: “There is NO SUCH THING as a ‘rated watt'”. Their reasoning is worth knowing: a motor’s output is set by its torque and its RPM, through the relationship power = torque × RPM × 0.104. The same 20 Nm of torque produces about 209 W at 100 rpm and about 628 W at 300 rpm. Identical motor, triple the “rating”, depending only on how fast the wheel is turning.
That is why climbing is hard on hardware: the wheel turns slowly while torque demand peaks — the worst possible combination. For the full picture of how motor, controller and sensors share that job, see our guide to how e-bikes actually work — motors, sensors and controllers.
What turns watts into heat instead of motion?
Copper resistance. Current flowing through the motor windings turns part of your battery’s energy into heat, and that loss scales with the square of current — the I²R relationship. Grin spell out the consequence: doubling the current multiplies copper heating by four. Ask for twice the torque and you create four times the waste heat.
Timing matters as much as the number. Grin note that a hub motor takes one to two hours to reach a steady temperature, while a real climb lasts five to ten minutes. That mismatch is why a short Sydney hill is survivable even at 700–800 W of draw, and why a twenty-minute climb at the same power is not.
Grin’s own measurements make the controller’s role plain. The same Crystalyte H3540 hub motor on a 36 V pack produces about 600 W of peak output with a 20 A controller, and about 1058 W with a 40 A controller. On a 52 V pack with the original 20 A controller it reaches about 840 W. The motor never changed. Peak power is overwhelmingly a controller-and-battery number.
How many watts can your own legs add?
More than most riders assume, in short bursts. Grin’s torque-sensor calibration example is a useful yardstick: a 60 kg rider standing on a 165 mm crank applies roughly 97 Nm. Put that through the same power relationship at 60 rpm and you are briefly making around 600 W at the cranks — more than the motor in most legal e-bikes.
The catch is duration. Nobody holds a standing effort for a kilometre, and what a rider contributes across a whole commute is far lower and steadier. That is precisely why pedal assist works: the motor covers the part you cannot sustain. We have not put a figure on sustained human output, because it varies enormously between riders and we cannot verify one from a source we trust on motors.
How do watts turn into range on a real pack?
Divide watt-hours by watt-hours per kilometre. Energy in a battery is volts × amp-hours: a 48 V, 25 Ah pack holds 1,200 Wh. At the 8.5 Wh/km our table gives for 25 km/h on the flat, that pack is theoretically good for about 140 km. The 2026 Cyberbikes Centauro carries exactly that pack — 48 V 25 Ah (1,200 Wh) Samsung cells — and the product page claims up to 120 km at 25 km/h, measured on a flat road with a 75 kg rider and no headwind, recharging in about five hours.
The gap between our 140 km and the claimed 120 km is the honest margin: real roads have stops, rises, wind and a rider who is not exactly 75 kg. Now apply the hill row. At 31 Wh/km the same 1,200 Wh pack gives under 40 km. Terrain, not the badge on the motor, sets your range.
Does NSW law limit the watts you can legally use?
Yes, and the limit is about continuous rated power, not about the peak your controller can briefly deliver. Transport for NSW currently allows a maximum of 500 W continuous power, dropping to 250 W from 1 March 2029. The motor must stop providing power above 25 km/h, and any throttle-only function must cut out at 6 km/h. From 1 March 2029, only EN 15194 certified e-bikes will be allowed on NSW roads.
One line on that page catches people out: e-bikes exceeding any of these limits are illegal even if the power or speed is restricted by software. A 1,500 W motor dialled down in a menu is still a 1,500 W motor in law — and NSW seizure and crushing laws took effect on 21 August 2026.
Put that beside the table and the picture resolves. A compliant 500 W system comfortably covers flat commuting at 213 W of draw, and handles short Sydney climbs on the strength of the short-burst behaviour Grin describe. The Centauro runs a 250 W rear hub motor, with pedal assist cutting out at 25 km/h and the throttle limited to 6 km/h, and the product page lists UL 2849 for the e-bike system, UL 2271 for the battery, and ISO 4210 for the frame.
What does this mean for a Leichhardt commute?
- Chase watt-hours, not watts. Range comes from pack size and how hard you ride, not from the motor’s badge.
- Ease off five km/h on the flat and you cut battery draw by around a third. That is the cheapest range upgrade there is.
- Gear down and keep the wheel turning on climbs. Low RPM with high torque is the heat-producing combination; spinning a little faster is kinder to the motor.
- Judge a motor on how long it holds power, not on peak numbers. A five-minute climb is the real test.
- Check compliance before you buy. Software limiting does not make an over-powered bike legal in NSW.
One last bit of perspective: all of this energy is trivial next to driving. Our short video makes the comparison concrete.
Frequently Asked Questions
How many watts is enough for an e-bike in Sydney?
For flat commuting at 25 km/h, roughly 213 W of battery draw is enough on a 110 kg bike-and-rider system. A legal NSW e-bike rated to 500 W continuous has ample headroom for that, and the short bursts that Sydney’s steeper streets demand. Watts matter less than whether the motor can hold power for the five to ten minutes a climb lasts.
Does a bigger motor give you more range?
No. Range comes from watt-hours in the battery divided by watt-hours used per kilometre. A 1,200 Wh pack at 8.5 Wh/km gives about 140 km in flat, still conditions, and under 40 km on a sustained 6% climb at 31 Wh/km. A larger motor does not change either number; how fast you ride and how hilly your route is does.
Why does riding faster drain an e-bike battery so quickly?
Air drag grows with the square of speed, so the power needed to push through it grows with the cube. Going from 20 km/h to 25 km/h lifts battery draw from about 131 W to about 213 W on our figures — a 63% increase for 5 km/h. Dropping your cruising speed slightly is the single most effective way to add range.
Try it on a real Sydney hill
Numbers on a page are one thing; the feel of a motor holding power halfway up a climb is another. Cyberbikes is at 281 Parramatta Road, Leichhardt, open Tuesday to Saturday — call 0491 794 668 and book a test ride on the Centauro, or start on our rent-to-own plan from $99 a week. If you want the background first, start with our guide to e-bike motors, sensors and controllers.
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