E-bikes: A New Revolution on Two Pedals

How it works: sensors, controller, assist modes

An e-bike's operation comes down to three stages. A sensor detects the rider's pedaling, a controller uses that signal and the selected mode to calculate how much current to send to the motor, and the motor adds that much force. Because this loop repeats dozens to hundreds of times a second, the rider feels less that a machine is stepping in and more that "my legs suddenly got stronger". Which sensor is used and how finely the controller responds are the biggest factors in how the bike feels to ride.

Cadence sensor vs torque sensor

A cadence sensor uses a magnet ring and a Hall sensor around the crank to detect whether the pedals are turning. When the pedals start turning, a set output switches on; when they stop, it switches off. It's that simple. It's cheap and reliable, but because the motor delivers its set power even if you barely turn the pedals, it can lurch forward when you set off, and since the amount of assistance isn't linked to how hard you push, it feels less natural. It's mostly found on budget models with hub motors.

A torque sensor measures tiny twisting or deformation in the crank spindle or rear dropout to read how hard the rider is actually pushing. It enables proportional control, helping a lot when you push hard and a little when you push lightly, which feels closest to riding an ordinary bike. Because assistance rises at exactly the moment you push on a climb, the battery is used efficiently too. Most mid-drive systems use a torque sensor as standard, and many now blend in cadence and speed data to refine the response.

Controller and assist modes

The controller is the e-bike's brain. It combines sensor signals, wheel speed, battery voltage and temperature, and the assist mode the rider has chosen to decide the motor current. It's also the controller's job to taper off assistance as you near the legal speed and cut it completely at 25 km/h, and to limit output when the battery gets too hot. Changing modes on the handlebar display or remote changes the ratio of motor assistance to rider effort; names vary by manufacturer, but there are usually four or five levels, such as Eco, Tour, Sport and Turbo. For example, Eco mode might add 50–60% of the rider's power and Turbo mode 300% or more. Recent models also offer an "Auto" or "e-MTB" mode that adjusts assistance automatically to the situation.

Another feature worth knowing is walk assist. While you hold a button, it pushes the bike along at a walking pace of around 6 km/h, which is handy when pushing a heavy e-bike up a ramp. It moves the bike without pedaling, but because it's limited to walking speed, it's allowed in most countries.

Types of motor: hub motor vs mid-drive

E-bike motors fall into two broad groups by where they're mounted: hub motors and mid-drives (center motors). A hub motor sits inside the hub (the center of the wheel) of the front or rear wheel and turns the wheel directly. A mid-drive sits at the bottom bracket, where the cranks are, adding its force to the chainring so it reaches the rear wheel through the chain and gears. Neither is better across the board; their pros and cons divide clearly by use and budget.

Hub motors: simplicity and price

Hub motors are simple and independent of the drivetrain, so they put no extra load on the chain or sprockets. They're cheap, and they have the practical advantage that if the chain comes off, the motor can keep you going. Geared hubs with internal reduction gears are small and light with good starting torque, while gearless direct-drive hubs are nearly silent and very durable but heavy. The downside is that the motor is tied to the wheel's rotational speed and gets no benefit from the gears. On long, steep climbs the motor struggles at low revs and easily overheats, and with the weight concentrated in one wheel, handling becomes a little sluggish. A front hub motor can make the front wheel feel like it's slipping on wet roads or gravel, and a rear hub motor makes puncture repairs a chore because you have to disconnect the wiring.

Mid-drives: efficiency and natural feel

A mid-drive uses the bike's own gears, so when you shift to a low gear on a climb, the motor can stay at an efficient speed too. It's easier to get stronger climbing and longer range from the same battery, and with the weight concentrated low in the center of the bike, it keeps a balance similar to an ordinary bike. Paired with a torque sensor it feels very natural, and it has become the de facto standard for e-MTBs and premium city bikes. On the other hand, it's expensive, and because the motor's power also passes through the chain and cassette, the drivetrain wears faster. Shifting under heavy load can make the chain jump or get noisy, so you need to get into the habit of easing off the pedals slightly as you shift.

All about batteries

The part that most determines an e-bike's price, weight and range is, without question, the battery. Battery spec sheets list V (volts), Ah (amp-hours) and Wh (watt-hours), and the figure directly linked to range is Wh. Wh is the total stored energy, calculated as voltage (V) × capacity (Ah). For example, a 36V 14Ah battery holds 36 × 14 = 504Wh, and a 48V 10.5Ah battery also holds about 504Wh, so the two store almost the same energy. If a product page only boasts about high Ah, multiply by the voltage too for a fair comparison.

Cell types: 18650 and 21700

An e-bike battery is a "pack" made up of dozens of cylindrical lithium-ion cells. The longest-established format is the 18650 cell, 18mm in diameter and 65mm long, with a nominal voltage of about 3.6V and a capacity of usually 2.5–3.5Ah. Recently the 21700 cell, 21mm in diameter and 70mm long, has been spreading fast. Each cell can hold about 4–5Ah, so the same capacity needs fewer cells, and fewer connections also help reliability and heat dissipation. Connecting cells in series (S) raises voltage; connecting them in parallel (P) raises capacity. A 36V pack is typically "10S", with ten cells in series, and a 48V pack "13S".

Lifespan and charge cycles

Lithium-ion batteries lose a little capacity with use. A "charge cycle" means charging the equivalent of 100% of the battery's capacity, so two 50% charges count as one cycle. It varies by manufacturer and cell quality, but e-bike batteries are generally said to drop to about 70–80% of their original capacity after around 500–1,000 cycles. For someone commuting 10km a day, that means years of use without much inconvenience. What shortens battery life most is heat, full discharge, and being left at 100% for long periods.

That's why experts recommend using and charging between 20% and 80% day to day. Charging to 100% the night before a long ride is fine, but avoid leaving it fully charged for days on end. In winter or when you won't ride for a long time, set it to around 40–60% and store it indoors somewhere cool and dry (roughly 10–20°C), checking the charge every month or two and topping it up if it has dropped too far. At sub-zero temperatures, chemical reactions slow down and capacity and output temporarily fall; this is normal, not a fault. However, charging a frozen battery right away risks lithium metal plating inside the cells, so let it warm up fully at room temperature before charging.

Fire safety: rules you must follow

Because lithium-ion batteries hold so much energy, damage can lead to "thermal runaway": one overheated cell spreads heat to its neighbors, setting them alight in a chain reaction that ordinary extinguishers struggle to put out and that releases toxic gases. Many of the fires involving electric mobility devices reported in Korea and abroad are linked to uncertified chargers, modified or rebuilt batteries, batteries that have taken an impact, and long periods of indoor charging.

What determines range

"How far will it go on one charge?" is the most common question about e-bikes, but the answer is always "it depends". The same 500Wh battery can easily go well over 100km cruising slowly on the flat in Eco mode, yet struggle to reach 30km climbing mountain roads in Turbo. The energy an e-bike uses breaks down into rolling resistance (tires and road), air resistance (proportional to the square of speed) and climbing resistance (weight × gradient), and the assist mode decides what percentage of it the motor covers.

So the best unit for understanding range is Wh/km, the energy used to travel 1km. Flat commuting typically uses about 5–10Wh/km, while hilly routes or high assist modes often use 15Wh/km or more. Divide the battery capacity by this figure and you get a rough range. The calculator below shows estimates from a simplified physics model based on this principle.

E-bike law in Korea

In Korea, the legal definition of an e-bike is found in the Act on the Promotion of the Use of Bicycles (the "Bicycle Act"). It defines an "electric bicycle" as a bicycle fitted with an electric motor to supplement human power that meets all of the following requirements.

1. It must be propelled by the pedals (including hand pedals) and the motor together, and must not move on the motor alone — in other words, it must be pedal-assist (PAS).
2. The motor must not operate at speeds of 25 km/h or more — from 25 km/h you must ride on human power alone.
3. The total weight of the bicycle, including attached devices, must be under 30kg.

Pedal-assist e-bikes that meet these requirements and have passed safety confirmation under the relevant safety standards (such as KC certification) are legally treated as "bicycles" and, since March 2018, have been allowed on bike paths. No driver's license is needed, and there's no requirement for a license plate or insurance. However, children under 13 are not permitted to ride e-bikes, and as with bicycles, wearing a helmet is mandatory.

How throttle e-bikes differ

Throttle e-bikes, which run on the motor alone when you twist a grip or press a lever on the bars, without pedaling, fail the first requirement above, so they are not "electric bicycles" under the Bicycle Act. Under the Road Traffic Act they're classed as motorized bicycles, and those certified with a top speed under 25 km/h and a vehicle weight under 30kg are treated, like e-scooters, as personal mobility devices (PM). Personal mobility devices require at least a motorized bicycle license (age 16 and over), and riding without a helmet or carrying a passenger incurs fines or penalties. Throttle vehicles outside these limits are ordinary motorized bicycles (two-wheeled vehicles) and may carry additional obligations such as registration and insurance. "Dual" models with both pedal assist and a throttle are easy to misclassify, so before buying, always check which standard the product was certified under.

International rules compared

Each country approaches e-bike regulation with a slightly different philosophy. The European Union, based on the European standard EN 15194, treats pedal-assist bicycles (pedelecs) with a rated continuous power of 250W or less and assistance that cuts out at 25 km/h the same as ordinary bicycles. Walk assist at walking pace (up to 6 km/h) is allowed, but faster throttles are not permitted in principle. "Speed pedelecs (S-pedelecs)", which assist up to 45 km/h, fall into a separate motorcycle category (L1e-B) with requirements such as a license plate, insurance, a license and a helmet.

In the US, federal law defines low-speed e-bikes with under 750W and a motor-only top speed under 20mph (about 32 km/h) as consumer products, and many states subdivide them into a three-class system that determines where they can be ridden. Japan, unusually, regulates by "assist ratio": at low speeds the motor may add up to twice the rider's effort, but the ratio shrinks as speed rises, reaching zero at 24 km/h.

* Korea's Bicycle Act sets criteria on speed, weight and mode of operation; detailed power and safety requirements are covered by the safety confirmation standards. In the US, detailed rules vary greatly from state to state, so check the law in the relevant state. Class 2 and 3 products bought abroad may not meet Korean standards.

Types of e-bike

E-bikes now come in as many forms as ordinary bicycles. They share a motor and battery, but frame design, drivetrain and battery placement differ completely depending on use. Here are the four main types. For the classification of ordinary bikes, see the 02 Bike types chapter.

Buying guide: seven questions for a choice you won't regret

E-bikes cost more than ordinary bikes, and with a battery and electronics, after-sales care matters. Rather than deciding on looks and price alone, answer the following questions one by one and the right model will naturally come into focus.

1. Where will you ride, and how far?

Start by noting your daily round-trip distance and the gradients on your route. For a mostly flat 20km round-trip commute, a battery of around 400Wh and a hub motor are plenty, but in a hilly neighborhood a mid-drive with a torque sensor makes a big difference to satisfaction. Use the range calculator above and choose about 1.5–2 times the capacity you need, and you'll have peace of mind even as the battery ages or winter arrives.

2. Does it meet Korean standards and certification?

Check that it's pedal-assist, that assistance cuts out at 25 km/h, that its total weight is under 30kg, and that it carries the safety confirmation (KC) mark. Products bought directly from overseas or with a throttle may not meet the Korean requirements for an "electric bicycle". It's also worth checking separately whether the battery and charger are certified.

3. Who makes the motor and battery system?

Long-term satisfaction depends on whether the motor, battery and display form one company's integrated system, and whether that company has an official service network in Korea. Be sure to ask whether genuine batteries will be available when you need a replacement in three to five years, and whether there's a nearby shop that can run the diagnostic software. With cheap no-name systems, sometimes parts can't be found when something fails, leaving the whole bike unusable.

4. Does it fit you, and can you lift it?

An e-bike is still a bike. If the frame size, standover height and bar position don't suit your body, it'll be uncomfortable motor or no motor. Fitting is covered in detail in the 04 Assembly & fit chapter. And if you'll need to carry it up apartment stairs, into an elevator or onto a car rack, it's important to lift it for real. Check, too, whether the battery is removable and what the bike weighs without it.

5. Are the brakes and tires up to it?

E-bikes are heavier than ordinary bikes and ridden at higher average speeds, so braking performance is especially important. Hydraulic disc brakes are the top recommendation, and "E-Bike Ready" tires designed for e-bike loads resist punctures and wear better. Whether practical equipment such as fenders, lights and a rack comes as standard also makes a big difference to the total cost.

6. Have you test-ridden it?

The difference between cadence and torque sensors, and between hub and mid-drive motors, becomes obvious within minutes of riding. If possible, be sure to test three situations: setting off, slow turns and climbing. Whether it lurches forward when you set off and whether assistance cuts out instantly when you stop pedaling bear directly on safety.

7. Have you worked out the total cost of ownership?

Besides the purchase price, factor in battery replacement (several hundred thousand won), how often consumables need replacing, and storage and theft-prevention costs. If theft worries you, GPS tracking or theft insurance is worth considering. Compare with driving and public transportation using the commuting cost calculator below to estimate the payback period.

Care and troubleshooting

The mechanical parts of an e-bike — chain, brakes, tires, gears — are cared for exactly as on an ordinary bike. But with the extra weight and torque they wear faster, so it's a good idea to shorten your service intervals a little. For basic maintenance, see the 05 Repair chapter; here we cover care specific to the electrical system and what to do about common symptoms.

Battery care habits

Let a battery that's hot from a ride cool for about 30 minutes before charging, and unplug the charger when charging is done. Wipe the terminals with a dry cloth to remove dust and moisture, and when washing the bike, remove the battery and clean it with a damp cloth or low water pressure rather than a pressure washer. Leaving the battery in a car in summer or in direct sunlight is bad for both its life and safety.

Motor and drivetrain

On a mid-drive, the chain can wear 1.5–2 times faster than on an ordinary bike, so check it often with a chain wear gauge. Neglect a stretched chain and you'll have to replace the expensive chainrings and cassette along with it. If the motor grinds or clunks, suspect loose crank bolts, worn bearings or damaged internal gears. Most motor housings can't be opened by the user, and taking one apart yourself voids the warranty, so use an official service center.

Diagnosing sensor and electrical errors

When an error code appears on the display or assistance suddenly cuts out, the cause is often surprisingly simple. The table below lists common symptoms and checks you can try yourself first. Error codes mean different things for each manufacturer, so check the manual as well.

Riding safely: helmets, speed, stopping distance

The biggest danger of an e-bike is that it lets you go faster than your fitness would. Someone who rode at about 15 km/h on an ordinary bike can hold 23–25 km/h on an e-bike without much effort. The problem is that drivers, pedestrians and other cyclists don't expect that speed. A driver at an intersection turning because they assume "it's a bike, it'll be slow" is a classic e-bike crash pattern.

Speed and weight feed directly into stopping distance. Kinetic energy is proportional to mass and to the square of speed, so 25 km/h carries about 2.8 times the energy of 15 km/h. At 25 km/h you travel about 7m during one second of reaction time, and once you add the braking distance on a dry surface, it easily exceeds 10m. On wet roads it's longer still. That's why an e-bike needs good brakes, bright enough front and rear lights, and a well-fitting helmet.

If you're new to e-bikes, practice starting and stopping several times in the lowest mode in a quiet open area. In particular, if you're stopped with a foot on the pedal in a high mode, the bike can suddenly jump forward the moment you absent-mindedly put weight on the pedal. Make a habit of lowering the mode or taking your foot off the pedal while waiting at lights. At night, being seen matters as much as switching on your headlight, so reflective clothing and a flashing taillight make a good combination.

Environment and cost: is it really worth it?

The e-bike uses remarkably little energy per kilometer traveled. Even at 10Wh/km on a flat commute, that's only a few percent of the energy an ordinary car uses to cover the same distance. Even including the carbon emitted in generating electricity, an e-bike's emissions per kilometer are lower than a car's, and lower than most public transportation. Of course, making the battery and motor also emits carbon, and at the end of its life the battery must go through a recycling system. Even so, if it replaces some car journeys, the environmental benefit is clear.

The same goes for cost. The electricity itself often comes to just a few tens of thousands of won even if you ride all year; most of the real cost is battery depreciation (replacement cost divided by lifetime distance) and consumables such as tires, chains and brake pads. Enter your own commuting conditions in the calculator below and try changing the assumptions shown in gray to compare.

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