A bigger wheel doesn’t weaken your e-bike motor — it re-gears it. Lace the same hub motor into a larger wheel and it spins at the same RPM but pushes the bike further per turn: going from 26″ to 29″ you gain roughly 11% road speed and give up roughly 10% of the thrust at the tyre. Nothing inside the motor changes — only the lever it works through. That one fact decides how your e-bike climbs Sydney’s hills, how hot the motor runs and how far 1,200 Wh takes you.
Wheel size never appears on a spec sheet next to “motor power”, which is why it gets missed. At Cyberbikes in Leichhardt we’re asked constantly why one 250 W e-bike walks up Norton Street while another of the same rating struggles. Often the answer is sitting in the rim diameter.
Why does wheel size change torque at the road?
A hub motor produces torque — a twisting force in newton-metres — and the wheel is the lever that turns it into a push against the road. Thrust at the tyre is motor torque divided by the wheel’s rolling radius. Bigger radius, smaller push.
The arithmetic is blunt. A 29″ wheel is about 1.115 times the diameter of a 26″. At any motor RPM you travel about 11.5% faster; at any motor torque you get about 10% less thrust. Grin Technologies, whose motor simulator at ebikes.ca treats wheel size as a variable, puts it plainly: “thrust naturally increases as you select smaller wheel sizes.”
This is why cargo and delivery e-bikes so often run 20″ wheels. They aren’t slower by accident — they’re geared down on purpose, trading top speed for the ability to drag a heavy load away from a standstill without cooking the windings. A mid-drive does the same thing with a cassette; a hub motor has only one gear, and the wheel is that gear. For the full drivetrain picture, see our guide to how e-bikes actually work: motors, sensors and controllers.
Does a bigger wheel change your motor’s watts?
Not the rating stamped on the motor — but it absolutely changes the power that motor can safely produce. Grin’s page on e-bike motor power ratings is the clearest explanation of this anywhere, and it starts from a relationship worth memorising:
Power in watts = torque × RPM × 0.104
Power is torque multiplied by how fast you spin. So a motor held to a fixed torque limit makes more watts the faster it turns. Grin gives the worked example: “A motor producing 20 Nm of torque and spinning at 100 rpm is generating 209 watts. That same motor producing 20 Nm of torque while spinning at 300 rpm is producing 628 watts.” Same motor. Same torque. Triple the power, purely from RPM.
Now apply that to wheels. Grin states it directly: “If the motor is rated to produce 500 watts continuously at 20mph… in a slow 10mph bike you could assume it’s a 250 watt continuous motor.” And on wheel size: “If you are lacing the motor in a smaller 20″ diameter wheel, then even at 20mph it would be 650 watts rather than 500 watts because of the higher wheel RPM.”
Read that twice. The same physical motor is honestly a 250 W, 500 W or 650 W motor depending on the wheel it sits in and the speed you run it at — which is why Grin concludes that “hub motors should be rated by how much torque they can produce rather than how many watts”.
Why does a smaller wheel run cooler on a climb?
Because heat follows current, and current follows torque — not speed. Grin is emphatic on this point: “It’s not the output power but the output torque of the motor which causes it to heat up and eventually fail.”
The mechanism is copper loss, and it is brutally non-linear. In Grin’s words: “If you double the current through the windings in order to have double the torque and power from the motor, then you increase the amount of copper heat being generated by a factor of FOUR (the I²R relationship).” Ask for 30% more torque and you make about 69% more waste heat.
Picture two identical motors grinding up Darling Street at 12 km/h. The one in the 26″ wheel turns about 11% faster for that road speed, so it needs about 10% less torque — and therefore roughly 18% less winding heat — for the same push. The 29″ motor turns slower, pulls more current and heats faster. Grin also notes a hub motor takes “upwards of 1-2 hours” to reach steady-state temperature while a typical climb lasts “5-10 minutes”, which is why a bike can feel fine on a short pinch and still cook itself on a long one.
The ebikes.ca simulator reports motor overheat time and final temperature after two hours alongside power and efficiency, with wheel size as an input — the fastest reality-check available. For the winding side of the same problem, see our breakdown of fast-wind vs slow-wind hub motors and hill climbing.
Does a bigger wheel cost you range?
Slightly, but not for the reason most riders assume — and the effect is small enough that tyre choice and riding style swamp it.
Start with what your battery holds. Watt-hours = volts × amp-hours. The Cyberbikes Centauro carries a 48V 25Ah (1200Wh) Samsung lithium-ion battery: 48 × 25 = 1,200 Wh. Range is that number divided by your consumption in watt-hours per kilometre — at 10 Wh/km, 1,200 Wh is 120 km of arithmetic; at 20 Wh/km it is 60 km. Your real figure depends on weight, wind, hills and assist level, which is why the ebikes.ca simulator asks for gross vehicle weight, grade, headwind, CdA and rolling resistance before estimating Wh/km.
Wheel size enters in two small, opposing ways. A larger wheel rolls over Sydney’s patched tarmac at a gentler impact angle, marginally reducing rolling resistance. Against that, it forces the motor into a lower-RPM, lower-efficiency part of its curve on climbs — Grin’s graphs show “the motor is less and less efficient as it slows down”. On a flat Inner West commute the two roughly cancel; on a hilly route the smaller wheel usually wins on watt-hours.
One warning: change wheel size and your speedo and odometer read wrong until the controller’s wheel-diameter setting is updated. A display calibrated for 26″ on a 29″ wheel under-reads speed by about 10% — which matters legally in Australia.
Does wheel size affect NSW e-bike law?
The law is written about power and speed, not rim diameter — but wheel size affects both of the things the law measures, so it matters more than it looks.
Under the rules published by Transport for NSW, a legal e-bike has a maximum continuous rated power of 500 watts, a motor that “does not provide power at speeds higher than 25km/h”, and any throttle-only function cutting out at 6 km/h. Transport for NSW is explicit: “E-bikes that exceed any of these limits are illegal, even if the power or speed is restricted by software (app, switch or code).” From 1 March 2029, only EN 15194 certified e-bikes will be allowed on NSW roads, with the limit dropping to 250 W.
Two consequences follow. The 25 km/h cut-off is enforced by the controller reading wheel speed, so a mis-set wheel diameter can leave a bike assisting past 25 km/h while the display insists it’s doing 23. And a bigger wheel raises the motor’s unloaded top speed at the same voltage — exactly the kind of “small” change that can push a compliant bike over the line. Not theoretical: NSW Police and authorised officers gained expanded powers to seize and dispose of illegal e-bikes from 21 August 2026.
What wheel size should a Sydney rider actually choose?
For Inner West riding — stop-start traffic, steep pinches, loaded panniers, rough surfaces — a mid-size wheel with a wide tyre is the sweet spot, because it keeps the motor geared low enough to climb and cool while still rolling comfortably over broken road.
That is the reasoning behind the Cyberbikes Centauro running 26 x 2.4 e-bike-ready tyres rather than chasing 29″, paired with a Super 250W rear hub motor, the 48V 25Ah (1200Wh) Samsung pack, 100 mm front and 120 mm rear travel and 4-piston hydraulic brakes with 180 mm x 2.3 mm rotors. A bike rated for a 150 kg maximum rider and cargo load, a 50 kg rear rack and an optional 15 kg front basket needs gearing and stopping power to match. It is certified to UL 2849 for e-bike systems, UL 2271 for battery safety, and ISO 4210 for frame compliance, with a 250 W continuous motor.
Workshop rule of thumb: hilly route or carrying load, go smaller and wider — 27.5″ sits in the middle if you want some of both. Long flat runs where top speed beats launch, a bigger wheel earns its keep. And if you swap a hub motor between wheels, check the wheel-diameter setting on the display before your first ride.
Here’s the Centauro on real Sydney gradients:
Frequently Asked Questions
Does a bigger wheel make an e-bike motor weaker?
No — it re-gears it. The motor makes the same torque, but a larger wheel turns that torque into less thrust and more road speed per revolution. Going from 26″ to 29″ gives roughly 11% more speed and roughly 10% less thrust.
Why do cargo e-bikes use small 20-inch wheels?
Small wheels gear the hub motor down: more thrust, and higher RPM for the same road speed. Grin Technologies notes a motor rated 500 W continuous at 20 mph in a standard wheel would be a 650 W continuous motor in a 20″ wheel, because of the higher wheel RPM.
Can I put my hub motor into a different size wheel?
Mechanically yes, in most cases — but update the wheel-diameter setting in the controller or display, or your speed and distance readings will be wrong. In NSW that matters legally: assist must cut out at 25 km/h and the controller uses wheel speed to enforce it.
Does wheel size change my e-bike’s range?
Only slightly. Range is battery watt-hours divided by watt-hours per kilometre — a 48V 25Ah pack holds 1,200 Wh, so at 10 Wh/km that is 120 km of arithmetic. A bigger wheel slightly lowers rolling resistance but pushes the motor into a less efficient low-RPM region on climbs, so on hilly routes a smaller wheel usually uses fewer watt-hours.
Ride one before you decide
Numbers settle the theory; a hill settles the argument. Book a test ride at Cyberbikes Leichhardt, 281 Parramatta Road and take a Centauro up a real Sydney gradient — you’ll feel the gearing in the first hundred metres. Open Tuesday to Saturday; call 0491 794 668 to line up a time.
Technical data sourced from Grin Technologies (ebikes.ca) and Transport for NSW; Centauro specs as published on the Cyberbikes product page.
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