The Whopping Torque of Ebike Motors, an Engineering Masterpiece

The 250 Wh legal limit for European ebikes may seem a huge hindrance, until you experience their car-like torque.

The power of any electric motor is expressed in Watts. Since the European legislation for an electrically assisted bicycle stipulates that the motor must be 250 Watts maximum, stopping at 25 km/h and as soon as you stop pedalling, the first electric bikes of the 90s, equipped with heavy and weak lead batteries were quite slow. When it came to steep climbs, they had practically no advantage compared to a normal bicycle, their extra weight offsetting the limited power of their assistance. Then lithium ion batteries came, rendering ebikes quite more performant. Nevertheless, what enabled ebikes to swiftly accelerate and almost effortlessly overcome even steep climbs, was the increase in their torque, from an average 25 to 50 Newton meters (Nm) at the beginning of the century, to 40 to 85 NM for nowadays ebikes.

What is torque?

The concept of motor torque is in fact linked in double strand with the principles of physics and in particular of dynamics. Energy is a scalar quanitity, whereas torque is a vector. Torque is a measure of how much a force acting on an object causes that object to rotate. In other words, it is the mechanical moment of the forces exerted by the motor on the transmission, the attitude of those forces to trigger a rotation of a body about its axis.

The electrical power of the motor is expressed in Watts (limited to 250 Wh for ebikes) and the mechanical power is expressed in Newton per meter (Nm) which is the motor torque.

Being like the force delivered by the motor, torque value allows to distinguish the real power of the motor when it comes to tackling climbs and slopes, carrying heavy loads, or accelerating from a standstill.

One of the advantages given by electric drive, in fact, is that of having very high torque at low motor speeds. For instance, in an electric car and in a gasoline a car motor both delivering the same power, torque is at least 60% higher for the former. Just compare cars specifications.

Practical implications of motor torque for ebikes

Torque and acceleration: less efforts, more safety

The least powerful cars in Europe are limited to less than 70 hp and have about 85 Nm of torque (e.g. 67 Hp and 95 Nm for the cheapest Dacia Sandero 2023). The torque Nm value being the thrust exerted by the motor to rotate for one turn, one must reckon that, although these two values are similar, the ebike motor turns at a maximum 1000 turns per minute, versus the 7000 turns per minute of the gasoline motor. Since any ebike motor delivers the totality of its torque at the very start, with a Bosch performance CX, Yamaha Sync-drive or Shimano EP 8  (all with 85 Nm) equipped ebike, adding your leg power, you can start with a high gear (e.g. 6/10) and easily leap in front of such cars at the traffic light, at least for a good 20 m, giving their drivers plenty of time to see you and avoid hurting you inadvertently.

Since the first few pedal strokes at the start are usually the hardest, especially if you ride into traffic, the electric motor assistance will spare you time, energy and hassle, what makes riding an ebike much more pleasant than a normal bike, especially in congested traffic.

The stronger the torque, the less you need to shift gears

Each time something slows your riding pace, be it a climb, traffic or just your tiredness, you need to shift to a slower gear. This wears your drive (chain, shifter, cassette, chain ring) and retards you considerably. A strong couple, even when you slow down to 10km/h, allows you to keep riding in the fastest gears, thrusting you up to 25 km/h (electric motors assistance limit in the E.U.) within few seconds. Your average commuting will gain much speed and considerably spare your time.

Torque and climbs: the magical force

Perhaps the situation where you could most appreciate torque is when riding on a steep climb. The bigger your ebike torque, the lesser you will have to push on the pedals. I reckon that every additional 10 Nm of torque enable an ebiker to ride almost effortlessly on additionally 1 percentage point steeper climb. That is, with at 40 Nm ebike motor one can easily climb on a 4% steep road, with an 85 Nm ebike, even a 8.5% steep climb is easily overcome. That is for common ebikes weighing around 25 kg; there are carbon ebikes weighing less than 14 kg, which enable the same climbing performances with less torque.

You may wonder how much torque a 75kg individual’s leg power can deliver: roughly 120 Nm, more for strong athletes.

Torque and hauling: a wonder

The sheer fact of delivering all its torque from the very first turn, enables ebike motors to haul or even tow astonishingly heavy loads. Look at the video of a Haibike with a 85Nm Bosch motor towing a van.

The price of torque

You may have noticed that the higher the torque of an ebike, the more expensive it is. That is partially due to the fact that a powerful torque requires a tougher frame, suspensions, tires, wheels and so on, what adds to the price. Nevertheless, torque in itself is pricey. If we compare identically or similarly equipped 250Wh European ebikes available with two different motors having different torque values, we notice that each added Nm costs roughly 50 more euros. That is, the same ebike priced at €2500 in its 50 N meter version costs around €3000 in its 60 Nm version, provided that it exists.

We can estimate that ebikes with up to 42 Nm usually cost around €1000. That price doubles for ebikes with up to 55 Nm, whereas at least €2300 are needed to purchase ebikes with 60 to 70 Nm, and at least €2800 for ebikes sporting 85 Nm, which is the top of the range for the most common models. There are special, expensive models with impressive torques exceeding 100 Nm, like the potrayed Heritage Altitude with 120 Nm.

Torque sensor

The torque sensor (or power sensor) is located inside the motor. It measures the force that the cyclist exerts on the pedals, and accordingly adapts the power provided by the motor.

The finest ebikes, thanks to this sensor, deliver and assistance which is so smoothly harmonized with your muscular efforts, that you have the impression of riding or even swallowing steep climbs with just your leg power. To put it simply, the more you push on the pedals, the stronger the motor assistance. Impossible to just slowly turn the pedals to get the full motor assistance, like with ebikes without torque sensor. This will also allow a healthy biking exercise, without getting tired.