A Guide to Understand Hub Motor

Update:2017-03-06

Generally speaking, hub motors were the first type of drive systems for bicycles to be patented and they continue to be popular today. Instead of trying to integrate a motor into the bicycle drivetrain, hub motors stay completely separate. Electricity is run through copper wires to create electromagnets which repel traditional rare Earth magnets and create force that rotates the hub forward (and sometimes backwards). In the early days, brushed motors were used because they are inexpensive and require less sophisticated control systems but the brushes wear out over time and require replacement. These days, nearly every hub motor uses direct current.

Hub motors for bicycles are usually positioned at the middle of a wheel and when the bike is powered off, they function much like a traditional hub - connecting the tire, rim and spokes to the axle. Spokes are flexible and light weight, they absorb some shock when riding but can come out of true over time. Regular bicycle maintenance is still required with an electric bike and one downside to hub motor design is that it adds additional weight to the wheel and requires extra wires to deliver electricity and communications about operation. This means that truing wheels and repairing flats require more effort.

So hub motors take the place of regular light weight hubs, connecting the wheel to the bicycle axle. As they receive electricity and spin, the bike is propelled forward and some of this energy is exerted into the frame at the dropouts. Usually, the sturdiest place to mount a hub motor is in the rear wheel, because these dropouts are reinforced and have four legs connecting them to the rest of the frame instead of just two on the front fork. These four arms consist of two seat stays and two chain stays.

In some cases, a front mounted hub motor is preferred because it allows an internally geared hub or continuously variable transmission CVT hub to be used in the rear. Some of the newest electric bikes combine an internally geared hub with a hub motor and are able to put both in the rear wheel.

Now that you’ve got an understanding for what a hub motor is, let’s talk about the benefits, drawbacks and ride quality. Hub motors tend to be peaky, meaning they operate best at medium and high speeds. This makes them zippy and satisfying no matter which gear you’re pedaling in but less efficient over a range of speeds, especially slower ones. For example, if you’re starting from rest going up a hill and try to accelerate with a hub motor, it may struggle and even shut itself off.

A big drawback to hub motors - neo-powers.com is that they position weight further out towards the end of the bike (either the front or back) which reduces balance. This can play a role when jumping a bike or taking it off road. Additionally, motor weight is built into the wheel which increases unsprung weight. In short, suspension can perform better if the elements it is suspending are lighter because they do not have to deal with as much inertia.