In Australia, a higher-voltage battery does not make a road-legal e-bike go faster. Pedal-assist e-bikes sold in NSW are limited to a 250-watt continuous motor that must stop assisting once you hit 25 km/h — and that cut-off applies whether your battery is 36V, 48V or 52V. What the extra volts actually buy you is quicker acceleration off the lights, stronger hill-climbing, and more range headroom, not a higher top speed. Below, the team at Cyberbikes in Leichhardt breaks down exactly how voltage turns into speed, why your motor stops accelerating, and what a bigger battery really changes for everyday riding in Sydney.
The short answer: physics sets the speed, but the law sets your ceiling
On an unrestricted motor, voltage really does set the top speed — more volts spin the motor faster. But every legal e-bike in Australia has a controller that limits assistance to 25 km/h, so that natural top speed is capped well before voltage becomes the bottleneck. Think of voltage as your engine’s redline and the 25 km/h assist limit as a speed governor bolted on top. Raising the redline does nothing if the governor kicks in first. So a 52V e-bike and a 48V e-bike will both assist you to the same legal 25 km/h — the 52V bike just gets there with a bit more urgency and holds it more easily up a hill.
How voltage actually turns into speed
To understand why volts control speed, it helps to know what each electrical number does. This is the same first-principles picture the motor engineers at Grin Technologies (ebikes.ca) use to characterise every hub motor they build.
Volts, amps and watts — which one is “speed”?
Power is simply volts × amps = watts. But the two ingredients do different jobs. Current (amps) sets torque: in a permanent-magnet motor, torque rises in direct proportion to current, so twice the amps means roughly twice the twist at the wheel. Voltage sets speed: the faster you want the motor to spin, the more voltage you need to push it there. That relationship is close to linear — the motor’s speed is proportional to the applied voltage. So if you want more grunt from a standstill you feed it more amps; if you want a higher spinning speed you feed it more volts. For a deeper walk-through of the three numbers, see our guide to what watts, volts and amps mean on an e-bike.
Why your motor stops accelerating: the back-EMF ceiling
Here’s the part most riders never hear. As an electric motor spins, it generates its own voltage that opposes the battery — called back-EMF, and it grows in direct proportion to motor speed (V = k × RPM). When you pull away from a stop the motor is barely turning, back-EMF is near zero, so a big current flows and you get strong torque. As you speed up, back-EMF climbs and starts cancelling out the battery voltage, so less current can flow and the push fades. The motor keeps accelerating until its back-EMF almost equals the battery voltage — at which point current drops close to zero and the bike can’t speed up any further. That is the motor’s natural top speed, and it is set by the battery voltage. Give the motor more volts and that ceiling rises; give it fewer volts and it drops. This is the real mechanism behind “more voltage = more speed” — but on a legal Australian e-bike the controller trims assistance at 25 km/h long before the back-EMF ceiling is reached.
48V vs 52V: does a higher-voltage battery make a real difference?
This is the most common upgrade question we get in the Leichhardt workshop. A 52V pack is only about 8% higher voltage than a 48V pack, so the difference is real but modest — and on a speed-limited bike you feel it in punchiness and hill-holding, not in a higher legal top speed. Here’s how the two compare on the things that actually matter to a commuter.
| What you care about | 48V system | 52V system |
|---|---|---|
| Legal assisted top speed (NSW) | 25 km/h | 25 km/h (identical — set by law, not volts) |
| Acceleration from a stop | Strong | Slightly quicker, crisper feel |
| Holding speed up a steep hill | Good | Holds a little better under load |
| Range from the same watt-hours | Baseline | Marginally more efficient (lower current for same power) |
| Compatibility | Very common | Check your controller is rated for it |
Notice the last row on efficiency. Because power is volts × amps, a higher-voltage system delivers the same wattage at lower current. Lower current means less energy wasted as heat in the wiring and windings (heating rises with the square of current), which is why higher-voltage builds tend to run a touch cooler and slightly more efficiently. It is a genuine engineering benefit — just not the “goes faster” one people expect.
What Australian law actually says about e-bike speed
In NSW and across Australia, a bike that assists you like a normal bicycle — no licence, no registration — must be a pedal-assist (pedelec) e-bike with a motor rated up to 250 watts continuous that cuts power once the bike reaches 25 km/h. There is also an older throttle-controlled category capped at just 200 watts. The key point for this article: the 25 km/h figure is a legal assistance limit written into the road rules, not a physical limit of the motor. You can still pedal faster than 25 km/h under your own steam — the motor simply stops helping. Fitting a higher-voltage battery to chase a higher top speed doesn’t just fail to help within the law; if it de-restricts the bike it can push it out of the legal e-bike category altogether, which affects insurance and where you’re allowed to ride.
So what does more voltage actually get you?
Plenty — just not a bigger number on the speedo. On a legal Sydney e-bike, a healthy voltage does three useful things. First, acceleration: more voltage headroom means the motor reaches assisting speed more eagerly from every set of lights on Parramatta Road. Second, hill-climbing: with more voltage in reserve the controller can keep feeding current on a grade, so the bike holds 25 km/h up an incline that would bog down a tired low-voltage pack. Third, range and consistency: a bigger battery measured in watt-hours (volts × amp-hours) simply stores more energy, and a higher-voltage pack tends to sag less under load, so assistance feels steadier as the battery drains. If you want the fundamentals behind all of this, our pillar guide on how e-bikes actually work: motors, sensors and controllers ties the motor, controller and battery together.
A real-world example: the Cyberbikes Centauro
Our Cyberbikes Centauro is a good illustration of voltage done sensibly. It runs a 48V 25Ah (1,200Wh) Samsung battery paired with a 250W rear hub motor, priced at $3,999. That 48V system gives it plenty of headroom for brisk, confident acceleration and steady assistance up Sydney’s inner-west hills, while staying comfortably inside the 250W / 25 km/h legal envelope. The battery is UL 2271-certified and the whole bike is built to UL 2849, ISO 4210 and EN 15194 standards — proof that the smart move isn’t chasing raw volts, but pairing the right voltage with a big, quality battery and a compliant controller. That combination is what turns “48V on a spec sheet” into a bike that feels effortless on a real commute.
Want to see how a well-matched 48V hub-motor bike rides in the real world? Here’s our full Centauro review:
Frequently Asked Questions
Does a higher voltage battery make an e-bike faster?
On an unrestricted motor, yes — voltage sets a motor’s top speed. But on a road-legal Australian e-bike the controller stops assistance at 25 km/h regardless of voltage, so a higher-voltage battery gives you quicker acceleration, better hill-climbing and more range, not a higher legal top speed.
Is a 52V e-bike better than a 48V e-bike?
A 52V system is about 8% higher voltage, so it feels slightly punchier off the line and holds speed a little better on hills, and it runs marginally cooler because it draws less current for the same power. Both assist to the same 25 km/h limit, so choose based on acceleration, battery capacity and controller compatibility rather than top speed.
Why does my e-bike stop speeding up even with power left?
Two things cap it. Legally, the controller cuts motor assistance at 25 km/h. Physically, as the motor spins faster it produces back-EMF that opposes the battery until almost no current can flow, which sets the motor’s natural top speed. On a legal e-bike you hit the 25 km/h limit first.
Is it legal to fit a bigger battery to go faster in NSW?
You can fit a higher-capacity battery for more range, but a legal pedal-assist e-bike must still be limited to a 250W continuous motor and cut assistance at 25 km/h. De-restricting the bike to exceed that can move it out of the legal e-bike category, affecting registration, insurance and where you can ride. When in doubt, ask the team at Cyberbikes Leichhardt.
Talk volts and speed with the Cyberbikes team
Trying to decide between 48V and 52V, or wondering why your current e-bike feels flat on hills? Come in for a test ride at Cyberbikes, 281 Parramatta Road, Leichhardt, and feel the difference the right voltage-and-battery match makes. Browse the range at cyberbikes.com, call us on 0491 794 668, or ask about our rent-to-own plans from $99.99/week.
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