Rated watts describe what an e-bike motor can hold more or less forever without cooking itself; peak watts describe the brief maximum your controller and battery can shove through it. Neither figure is standardised. Grin Technologies, who build and test hub motors for a living, put it bluntly on their motor power ratings page: there is “no standard or even consistent way to provide a numeric ‘watts rating’ for a motor system”, and the very same motor can be sold as 250 W, 500 W or 1000 W with every figure defensible. For riders in Sydney there is only one number with legal teeth, and it is the rated one: 500 W maximum continuous rated power.
What does a “rated watt” on an e-bike actually mean?
A rated watt is meant to be the power a motor can sustain indefinitely without its windings getting hot enough to fail. The trouble is that a motor is nothing like a kettle. A kettle draws its rated power the moment you switch it on. A motor spinning freely with no load produces no output power at all; load it up and output climbs, then falls away again as the wheel slows. Grin’s engineers go as far as saying there is “NO SUCH THING as a ‘rated watt'” for e-bike motors, and quote their own products as broad ballparks — 250-500 W, or 600-1200 W — rather than single numbers.
Even where a manufacturer is being honest, the number depends on choices they do not publish. Continuous ratings are usually quoted at a reference speed — a 26-inch wheel at 32 km/h, roughly 250 rpm. Grin points out that a motor rated 500 W at that speed implies about 750 W at 30 mph, and that dropping the same motor into a 20-inch wheel would give roughly 650 W instead of 500 W. Same copper, same magnets, three different “ratings”. If you want the long version of how the parts interact, our guide to how e-bikes actually work — motors, sensors and controllers walks through the whole chain.
Why is peak power really a controller-and-battery number?
Peak power is set by how much current your controller will pass and how hard your battery can push, not by the motor casting itself. Watts are simply volts multiplied by amps, so a 48 V pack feeding a 20 A controller can deliver about 960 W of electrical input, and whatever survives the losses comes out at the axle.
Grin’s worked example makes the point better than any spec sheet. One hub motor on a 36 V battery with a 20 A controller peaks at 600 W of mechanical output at 40 km/h, drawing 744 W of input below that speed and falling to zero output near 48 km/h. Swap in a 40 A controller and nominal peak input jumps to 1440 W, with 1058 W of output at 33 km/h. Move to 52 V with the same 20 A and you get 840 W peak output — less than the 40 A version on paper, yet it feels stronger at speed. Three “peak power” figures, one motor, and the difference is entirely in the electronics.
This is also where the marketing gets slippery. Some sellers quote input power rather than output. Grin describes a 72 V, 50 A kit advertised as “3600 watts” that realistically produces around 2000 W peak at the wheel and can sustain roughly half of that without overheating. Headline claims, they note, routinely overstate real peak output by at least 30 per cent, and sometimes by a factor of two or three.
Why does heat, not watts, decide what your motor survives?
Because the thing that destroys a motor is temperature, and temperature is driven by current through copper. Grin are explicit that “it’s not the output power but the output torque of the motor which causes it to heat up and eventually fail”. Resistive heating scales with the square of current, so doubling the current to double your torque does not double the heat in the windings — it quadruples it.
What that heat does is unglamorous and permanent: enamel insulation burns off the copper, nylon planetary gears soften and strip, magnets lose strength. Grin’s own example is a 45 mm MXUS stator sold as a 5000 W motor that reaches 100 °C at 250 rpm while producing only 800 W of output. Winding enamel may survive brief excursions of 150-180 °C, but almost nobody would rate a motor to run there continuously — and whether a manufacturer picks 100 °C or 120 °C as their ceiling swings the published continuous rating enormously.
The saving grace for everyday riders is thermal mass. A motor takes 1-2 hours to reach steady-state temperature, while a typical steep climb lasts 5-10 minutes. That gap is why a sensibly built hub motor can pull far more than its continuous rating up a hill and shrug it off. Ambient temperature matters too: the same motor tolerates noticeably more current on a cold Sydney winter morning than it does at 40 °C in a Western Sydney February.
Does a bigger peak number climb Leichhardt’s hills better?
Not reliably, because climbing is a torque problem and watts are torque multiplied by speed. Grin give the conversion as power in watts being roughly torque in newton-metres times rpm times 0.104. Run the numbers: 20 Nm at 100 rpm is about 209 W, while the identical 20 Nm at 300 rpm is about 628 W. The motor is working exactly as hard in both cases and heating at the same rate, yet one would be badged a 200 W motor and the other a 600 W motor.
That is why a high peak figure flatters a bike on the flat and tells you very little about Darling Street or the climb out of Rozelle. Grin’s view is that hub motors would be far better rated by torque, and that the specs riders would actually need — winding resistance, the rpm-per-volt constant, thermal behaviour — are almost never published. Their free motor simulator is the honest way to compare two motors at the speed and gradient you actually ride. If you are weighing up a specific pair of options, our breakdown of 250 W versus 500 W e-bike motors covers the practical trade-offs.
Which number actually matters under NSW e-bike law?
The rated one, and only the rated one. Transport for NSW currently defines a legal e-bike as having a maximum continuous rated power of 500 W, with motor assistance that reduces as you speed up and cuts out completely at 25 km/h, and any throttle-only function cutting out at 6 km/h. From 1 March 2029 that drops to 250 W and only EN 15194 certified e-bikes will be allowed on NSW roads. New seizure and crushing laws took effect on 21 August 2026.
Here is the part that catches people out: Transport for NSW states that a bike exceeding those limits is illegal even if the power or speed is restricted by software — an app, a switch or a hidden code does not make an over-powered motor legal. So a listing shouting “1500 W peak” is not a feature, it is a liability. Our complete guide to NSW e-bike laws has the full detail, and the video below shows how quickly accessories can push a bike into registration territory.
This is exactly why the Cyberbikes Centauro is built around a 250 W rear hub motor rated at 250 W continuous rather than a big peak headline. Its product page lists a 48 V 25 Ah battery — 1200 Wh, since watt-hours are volts times amp-hours — using Samsung cells, UL 2271 certified, with up to 120 km of range at 25 km/h on flat ground with a 75 kg rider and no headwind. The bike carries UL 2849, UL 2271, ISO 4210 and EN 15194 certification, which means it already meets the standard NSW will require from 2029. Four-piston hydraulic brakes on 180 mm rotors, 100 mm front and 120 mm rear suspension travel, 150 kg combined rider and cargo capacity, 37 kg with the battery in, and an 18-month warranty.
Frequently Asked Questions
Is a higher peak wattage always better on an e-bike?
No. Peak wattage is mostly a function of your controller’s current limit and your battery voltage rather than the motor itself, and Grin Technologies note that advertised peaks commonly overstate real mechanical output by at least 30 per cent and sometimes by two or three times. A high peak figure also does nothing to raise the torque your motor can sustain on a long climb, because that is limited by winding temperature.
Can an e-bike legally be sold as 1000 W in NSW if it is limited by software?
No. Transport for NSW states that bikes exceeding the limits are illegal even where the power or speed is restricted by software, an app, a switch or code. The legal limit is 500 W maximum continuous rated power with assistance cutting out at 25 km/h, falling to 250 W and mandatory EN 15194 certification from 1 March 2029.
Why does my e-bike lose power near the top of a long hill?
Because resistive heating in the copper windings rises with the square of current, so sustained high torque builds heat far faster than the motor can shed it. A motor takes 1-2 hours to reach thermal steady state while a typical climb lasts 5-10 minutes, so short efforts are fine, but a long sustained grind can push winding temperature high enough that the controller or your own motor efficiency pulls output back.
Come and ride one
Numbers on a listing are easy to print. The only honest test is twenty minutes on a real hill. Book a test ride at Cyberbikes Leichhardt, 281 Parramatta Road, browse the range at cyberbikes.com, or call 0491 794 668, Tuesday to Saturday. Rent-to-own starts from $99 a week if you would rather ride first and decide later.
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