Derestricting an Ebike: The Honest Accounting
The speed limiter is a few lines of firmware acting on a pulse count, which is why defeating it is so easy. Everything that follows from defeating it is the part worth reading.
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An ebike does not have a governor, a restrictor plate, or anything mechanical holding it back. It has a controller that counts pulses, converts them into a speed number, and stops sending current to the motor when that number crosses a threshold. There is no physical limit involved, which is why the modification is trivial and why the internet is full of people describing it.
What the internet is much less full of is a clear account of what you are actually trading away. Not vague hand-waving about legality, but the specific list: which certification the bike loses, what the label on the frame now misstates, what an insurance adjuster does with a modified vehicle, what happens to a brake system chosen for a lower speed, and what sustained high-speed current does inside a motor that has one path to shed heat.
This page explains the mechanism and then the bill. It is not a walkthrough, and it deliberately does not tell you which parameter to change on which display.
How the limiter actually works
Almost every ebike measures road speed the same way. A magnet passes a sensor once per wheel revolution, usually a spoke magnet beside a chainstay-mounted reed or hall sensor, or a magnet built into the disc rotor. The controller times the interval between pulses. It then multiplies by a stored wheel circumference, which comes from the wheel-size value in the settings menu, and that product is your speed.
So speed is not measured. It is calculated, from two things: how often the pulses arrive, and what the firmware has been told the wheel measures. Feed either input a lie and the calculation produces a lie.
When the calculated figure reaches the cutoff, the controller ramps assist down to zero rather than cutting it, because an abrupt loss of several hundred watts at speed is unpleasant. Above the cutoff the bike is simply a heavy bicycle. The limit is on assist, not on the bike.
The cutoff value is set to match a legal definition. In the US that is 20 mph for Class 1 and Class 2 and 28 mph for Class 3, under the three-class framework covered in ebike classes explained. In the EU and UK it is 25 km/h, roughly 15.5 mph, under the EN 15194 EPAC standard, alongside a 250 W continuous rating. The number is a regulatory boundary the firmware enforces, not an engineering limit of the motor.
The three common methods, and what each one really does
Every approach in circulation attacks one of the two inputs above. Understanding which one tells you what the side effects will be, because the side effects are entirely predictable.
Changing the wheel-size parameter
Tell a controller fitted to a 27.5 inch wheel that it is driving a 20 inch wheel, and it multiplies the pulse rate by a circumference roughly 70 percent of the true one. The calculated speed comes out proportionally low, so the bike is doing about 27 mph before the controller believes it has reached 20.
The side effect is not subtle. The same wrong number feeds the speedometer, the odometer, the trip meter, and any distance-based service interval. Your display now under-reads by the same factor forever. A bike showing 20 mph is doing 27, a 30 mile ride logs as 22, and every mileage-based maintenance reminder arrives late. This is the method most likely to work on a cheap bike with a generic display, and also the one that leaves you flying blind about your own speed.
Moving the speed sensor magnet
The controller counts one pulse per wheel revolution because that is where the magnet sits. Relocate the magnet so it passes the sensor at a much lower rate, typically by mounting it to something that turns at crank speed rather than wheel speed, and the pulse interval stretches enormously. The controller reads a walking pace while the bike is doing 25 mph.
This is the crudest version and it produces the crudest result. The bike will now show a speed of a few mph regardless of what it is doing, which means no usable speedometer, a meaningless odometer, and on some systems a plausibility fault, because the firmware can compare an implausible speed against cadence and assist load and conclude that something is wrong.
Dongles and tuning modules
A dongle sits in the speed sensor line and divides the pulse frequency, usually by two. The controller sees half the pulses, calculates half the speed, and does not cut assist until true speed is roughly double the cutoff. More elaborate modules switch behaviour above a threshold so that the display reads correctly at low speed and only diverges once you are moving, which exists specifically to make the modification harder to notice.
Dongles are the most popular route because they are reversible and require no menu diving. They are also the most visible: an added module in the sensor loom is a physical object a technician can see, and the signal pattern it produces is exactly what system diagnostics look for.
There is a fourth case worth separating out. Some kit-based systems, particularly Bafang mid-drives, expose the speed limit and wheel size as plain configurable parameters through a programming cable. That is not a hack, it is a settings screen. It carries every consequence listed below regardless, because the law cares about what the bike does, not how hard it was to make it do it. The controller is doing exactly what it is told either way.
Why modern systems catch it
Ten years ago a derestricted bike was invisible. Anyone still assuming that is working from old forum posts.
Brand-name mid-drive systems from Bosch, Shimano, Yamaha, and Specialized store operating data internally: motor revolutions, hours under load, error events, and speed history. Those internal counters and the odometer come from different sources, so tuning makes them disagree. A bike whose motor has turned enough revolutions for 4,000 miles but whose odometer reads 2,900 has told the diagnostic tool everything it needs to know. Several manufacturers went further and set a permanent flag when the system sees a speed signal it considers implausible, and the practical result at a dealer is a refused warranty claim.
What the bike becomes legally
This is the consequence people underrate, because nothing visible changes. The bike still has pedals, still looks like a bicycle, and still carries a sticker saying what class it is. That sticker is now wrong, and it is the sticker the law reads.
In the US, the federal definition of a low-speed electric bicycle turns on a motor under 750 W and a top motor-only speed under 20 mph, and the state-level three-class system layers assisted-speed cutoffs on top. Exceed the cutoff your bike is labelled for and it stops satisfying the definition of an electric bicycle in that state. It does not become nothing; it becomes whatever the state's next category up is, typically a moped or a motor-driven cycle, with the registration, plate, licence, insurance, and helmet requirements that category carries. What makes an ebike street legal works through the individual tests, and the practical upshot is that a derestricted bike fails at least one of them.
Europe is harsher. An EPAC that assists past 25 km/h or exceeds 250 W continuous falls out of the bicycle exemption entirely and lands in category L1e-B, which is a moped. Mopeds require type approval, and type approval is granted to a vehicle type by a manufacturer, not to an individual bike by its owner. There is no realistic path to registering a derestricted bicycle, so the machine is simply not roadworthy, and several countries treat riding one as riding an unregistered, uninsured motor vehicle.
Then there is access. Bike paths, rail trails, and park systems set their rules by class, and many exclude Class 3 already. Enforcement, where it exists, is a speed check rather than a spec check.
Warranty, insurance, and what happens after a crash
Three separate financial exposures follow, and they compound.
The warranty goes first, and broadly. Manufacturers do not void only the motor. Modifying the drive system typically voids the frame, battery, and electronics coverage together, on the reasonable argument that the whole system was validated as a unit. Given that a replacement mid-drive unit runs well into four figures and a name-brand 500 Wh battery typically costs $500 to $900, this is not a technicality.
Insurance is the one people never think about until they need it. Homeowners and renters policies that extend to bicycles, and specialist ebike policies, both underwrite a described item. Modifications that change the vehicle's legal classification sit squarely inside standard exclusions, and a claim that involves a crash will involve an adjuster who looks at the bike. Ebike insurance covers what these policies actually promise.
Liability is where it stops being about money you spent. If you strike a pedestrian at 30 mph on a machine that the law considers an unregistered motor vehicle, you are, in most jurisdictions, an uninsured motorist. Third-party injury claims are not capped by the value of your bike. This is the risk that makes the whole exercise look badly priced, and it is the one that never appears in the tutorial videos.
Brakes, tires, and the heat problem
The bike was engineered around a speed. Raising the speed does not raise the specification.
Brakes
Kinetic energy scales with the square of velocity, so it is not a linear increase. Going from 20 mph to 28 mph means the brakes have to absorb 1.96 times the energy, and from 20 to 32 mph it is 2.56 times. On a bike that already weighs 55 to 70 lb with a rider aboard, that lands on a rotor and pad set chosen for the lower figure.
The failure mode is fade rather than anything dramatic: repeated hard stops, or one long descent, heat the rotor and pads past their working range, the coefficient of friction drops, the lever pulls closer to the bar, and stopping distance grows exactly when you need it not to. Larger rotors, better pad compounds, and four-piston calipers all exist as answers, and ebike brakes explained covers what helps. None of it comes free with a dongle.
Tires
Ebike-rated tires carry an ECE-R75 marking, which certifies the casing for the loads and speeds of powered two-wheel use. Ordinary bicycle tires do not carry it, and plenty of budget ebikes ship without it. Sustained higher speed on a heavy bike means more casing flex per mile and more heat in the sidewall, and the result of running an underspecified tire hard is a sidewall failure at speed rather than a slow puncture. Ebike tires and wheels explains the marking.
Motor and controller heat
The power needed to overcome aerodynamic drag rises with the cube of speed, so pushing from 20 mph to 28 mph demands roughly 2.7 times the drag power, and the motor supplies most of that continuously rather than in bursts. Resistive heating in the windings rises with the square of the current, so a modest increase in sustained current produces a large increase in heat.
- Where the heat goes in a hub motor
- Into the motor shell, then to the air. There is no active cooling and the axle path is thin. A hub motor at sustained high current is a thermos with a heater in it.
- What overheats first
- Winding insulation and the magnets. Sintered neodymium magnets begin to lose field strength at sustained elevated temperature, and the loss is permanent. A weaker magnet means more current for the same torque, which makes more heat.
- Controller side
- MOSFETs and capacitors run hotter at higher continuous current. Controllers have thermal shutdown, which reads to the rider as random power loss on long efforts.
- What you notice
- Rollback partway up a long climb, reduced peak assist when hot, and over months a bike that feels flatter than it used to at the same settings.
Mid-drives are somewhat better placed, because they run through the gears and can stay nearer an efficient rpm, but they are also compact gearboxes with plastic reduction gears in many designs, and sustained high output is the condition those parts dislike most.
What it costs in range
Range is watt hours in the pack divided by watt hours consumed per mile, and speed is the largest single lever on the second number. This is arithmetic, not opinion.
A typical 750 W-class bike at a moderate assist level and 20 mph consumes around 18 to 25 Wh per mile. Push the same bike to 28 mph and the same rider commonly sees 30 to 40 Wh per mile, because drag has roughly doubled and the motor is doing a larger share of the work. A 500 Wh pack that gave you 22 to 27 miles now gives 13 to 17, and a hilly route is worse still.
People often respond by looking at range extenders and dual battery setups, which is worth investigating for its own sake but a poor answer here. You are adding 7 to 9 lb of battery to a bike whose brakes are already underspecified, in order to fund a consumption rate you created.
Buy the faster bike instead
If the reason you are reading this is that 20 mph is too slow for your commute, that is a completely legitimate complaint. Twenty miles an hour on a road with 40 mph traffic is genuinely unpleasant, and the answer the market already built for that problem is Class 3.
A Class 3 bike assists to 28 mph as designed. The brakes were chosen for it, the tires are rated for it, the frame was fatigue tested with it in mind, a speedometer is required, and the label on the down tube says what the bike does. You keep the warranty, the insurance stays valid, and there is no diagnostic flag waiting for you at the first service. Class 3 ebikes covers where you can and cannot ride one, which is the real trade, since many bike paths exclude them.
What derestricting gets you
- Assist continues past the cutoff, so less pedalling effort at 22 to 30 mph
- A dongle is reversible in minutes and costs far less than a new bike
- On a private property or closed-course machine, none of the legal issues apply
- On some old, simple, out-of-warranty hub bikes there is genuinely little left to lose
What it takes from you
- The bike no longer meets the class on its own label, so it is not a legal electric bicycle
- Warranty on motor, battery, electronics, and often frame is void
- Insurance may decline a claim, including third-party injury liability
- Brakes, tires, and frame were specified for the original speed and are not upgraded by the change
- Motor and controller run hotter continuously, which shortens their life and causes rollback
- Range falls by a third to a half at the higher cruising speeds
- Major systems log the modification permanently, which follows the bike to resale
There is one honest exception. If the bike is old, out of warranty, uninsured, has decent hydraulic brakes and ECE-rated tires, and will be ridden on private land, the ledger looks very different and most of that list evaporates. It is a narrow case.
The other exception is the manufacturer's own class switch. Several US brands ship bikes certified for more than one class and let you select between them in the display menu, with a label change to match. That is not derestricting. It is a supported configuration of a bike approved for both, and it is the correct way to get a higher cutoff on a bike that offers one.
If you are working out which class actually suits your riding, start with the class system and then real-world ebike speeds, which will tell you whether the cutoff is your problem at all. If it turns out that climbing rather than flat-road speed is what leaves you wanting more, choosing an ebike for hills is the more useful place to spend the money.