There are three main types of motors used to power electric bikes. Each has benefits for different types of riding.
Hub motors are the first type of drive systems for bicycles that had to be patented and still continue to be popular today. Rather than combining a motor into the bicycle drivetrain (this compliments the gears and the chain which the rider uses)hub motors remain completely separate. Electricity is made to pass through the copper wires creating electromagnets that repel traditional rare Earth magnets and generate a force which rotates the hub forward (sometimes backwards). During the early days brushed motors have been used since they are cheap and need less complicated control systems but the brushes wear out in time and need replacement. Nowadays, almost every hub motor (geared or gearless are brushless and make use of direct current DC).
How Hub Motors Work
Hub motors for bicycles are commonly positioned in the middle of the wheel and if the bike is powered off they function just like a traditional hub (connecting the tire, spokes and rim to the axle. Spokes are flexible and lightweight. They absorb shock when riding but could come out of true in due time. Regular maintenance of the bike is still needed with an electric bicycle and a disadvantage of the hub motor design is that they add extra weight to the wheel and extra wires that give electricity and communications during operation. This means that truing wheels and repairing flats need more effort).
So hub motors replace regular lightweight hubs, which connect the wheel to the axle of the bike. As the hub motors receive spin and electricity, the bike is moved forward and a bit of this energy is generated to the frame at the dropouts. Normally, the sturdiest place to put a hub motor is in the rear wheel since these dropouts are reinforced and have four legs that connect to the rest of the frame rather than just two on the front fork. The four arms consist of two seat stays and two chain stays.
Hub Motor Design
In a few cases a front mounted hub motor is chosen since it allows an internally geared hub or constantly variable transmission CVT hub like the NuVinci to be used in the back. A few of the latest electric bicycles such as the Smart ebike combine internally geared hubs which the cyclist pedals and a hub motor that can be placed both in the rear part. Now that you have an understanding about what a hub motor is, we can discuss the benefits , ride quality and drawbacks. Hub motors have a tendency to be torque vs. peaky which means that they function best at high and medium speeds. This makes a hub motor satisfying and zippy no matter what gear you pedal in but less efficient over speed ranges, especially slower ones. For example, if you are beginning from rest climbing up a hill and trying to accelerate using a hub motor, it could struggle and even turn itself off.
Pros and Cons of Hub Motors
A huge drawback to hub motors is that they can adjust weight further out towards the bike’s end (the front or the back) which reduces balance. This could play a big role when you jump a bike or take it off the road. In addition, motor weight is built into the wheel which increases the unsprung weight, which is the weight that could not be sprung as a part of the main frame. This could be a tricky idea. In short, suspension could perform better if the elements which are being suspended are lighter since they do not have to deal with a huge inertia.
Rear Hub Motors
Rear hub motors are the standard for electric bikes. The motor is located in the hub of the rear wheel. The motor powers the rear wheel of the bicycle by activating an electromagnetic coil of wire with electricity. This type of motor gives the rider the most traction because the bulk of the weight on a bicycle is located in the rear of the bicycle. The only drawback of the rear hub motor is that the amount of torque the rider gets from the motor is determined by the mechanical gears. The rider must be conscious of which gear he or she is in at all times to make the best use of the electricity in the battery. These motors can be very powerful, but they are often not the most efficient use of electricity.
Front Wheel Hub Motor
These are the same type of motor as a rear hub motor but they are on the front wheel instead of the rear wheel. These are usually used on three-wheel e-bikes and some e-bike conversion kits.
In the end, the hub motors let the rider choose whatever gear they want, pedal at any speed desired and allow varying force with every stride and not play a material role in the function of the motor.
Geared Hub Motors
Hub motors have two different kinds which include geared (usually a planetary design) and gearless or direct drive (depending on bigger magnets and no gears). Gears give leverage, which enable lighter weight and smaller motors to achieve bigger output and also cause wear, noise and friction. A lot of modern geared hub motors are designed very well and must last for many years so don’t be surprised. It could appear counterintuitive but geared hub motors do not provide more resistance when you cruise. The reason is that they usually have a freewheel mechanism which could detach from the axle and spin with small or no friction.
Gearless Hub Motors
The next kind of motor, gearless hub motors provide smooth, silent performance and are usually considered “flawless” by shops because of their simplicity. There is a glue inside which holds the magnets on the frame or canister which could become loose because of too much vibration and heat. Gearless hub motors depend solely on electromagnets and might not have a freewheel mechanism because if the magnets are powered off there is just a small amount of friction or magnetic resistance to overcome. Motors which are not freewheeling are known as direct drive and this really enables regeneration (the generation of electricity that is based on repelling magnets within the motor).
Not all the gearless direct drive hub motors provide regenerative braking or regen modes since you do not have to recoup a lot of energy this way (although it could help reduce wear on break pads). It is a cool feature but it is more expensive to implement and add complexity to the system. A few ebikes that offer regen are Specialized Turbo, all of the Stealth electric bikes and all of the BionX bikes and kits such as the Smart electric bike.
Gearless hub motors could require a huge casing (to provide space for the magnets) and weigh more ultimately. This is a generalization of course since the technology has changed to the point where a few direct drive hub motors could be quite lightweight and small. As already mentioned, hub motors independently operate from the rider’s pedaling. They could be geared or gearless, fit in the rear wheel, front wheel or even independently from the wheels just like the Organic Transit ELF, although it is very uncommon, and they could sometimes produce electricity. A few drawbacks of all hub motors might include increased unsprung weight, which could reduce traction, limit efficiency and rims and strain spokes. They might just have a single gear setting which could operate at a slower or faster speed but could not shift for improved speed or torque. They also tend to let wheels become more difficult to service such as fixing spokes or changing flat tires since they add weight to the wheel and need extra cables in order to deliver operation signals and electricity (except if they are all in one hub motor such as Copenhagen Wheel or FlyKly).
This type of motor is located in the crankset of the bicycle, where the pedals are. The electricity from the battery goes straight to the same place where the rider puts their energy to propel the bicycle. This doubling up of effort provides the best efficiency of the electricity used. Mid-drive motors offer the best torque capabilities for off-road electric bicycles as well.
As we change into mid-drive systems try to imagine a scenario where a rider with a hub motor driven electric bike approaches a steep hill, completely stops and then uses a twist throttle to move forward. The motor will likely struggle since it is made for flat surfaces and gives peak output as already mentioned. Let’s say the motor slowly pushes the rider forward and groans. By not pedaling along, a lot of hub motor designs just could not carry the average sized passenger upward a steep incline compared to the rest. This is where the rider can get into the benefits of a mid drive system.
Climbing is really where mid-drive motors shine. Not like a hub motor, the design lives at or near the bottom bracket (the point where the crank arms are linked to the frame for pedaling) and moves the chain forward rather than the wheel itself. Mid drive systems get the same benefit from a lot of the mechanical drivetrain systems just like the rider (the use of gears for climbing or going fast) and diminish unsprung weight. This is the best setup for efficiency (extending distance and ride) and climbing.
Pros and Cons of Mid-Drive Motors
Try to think of a full suspension electric mountain bike with a mid drive motor. The rear and front wheels could rebound quickly as well as efficiently because the weight is smaller and the total mass of the bike is connected to the central section of the frame thus causing it to be fluid. When you approach a big hill, the rider could shift to a low gear giving mechanical advantage thus making it easy to climb and pedal. Just as the rider gains advantages in this scenario so too will the motor. As the total speed of the bicycle is diminished for climbing, neither the rider, nor the motor are going to be over-exerted thanks to the gears. In this situation, the rear dropouts are going to take less strain since the weight as well of the force of the motor are connected and spread out to the major tubing of the lower bracket.
Advantages And Disadvantages of Gears in Mid-Drive Motors
- Gears have both an advantage and a disadvantage with mid drive systems since now, instead of the rider exerting force to the system (the chain, rear cassette cog teeth and the derailleur), the motor is applying force too.
- If you have changed gears while you pedal hard, you could remember the unwanted sounds and sensations of grinding, crunching and mashing.
- The teeth used to pull the derailleur arms and the chain from one sprocket to a different are sensitive and needs some finesse to properly activate.
- Doing this is going to extend the life of your bike and let you prevent cassette replacement and tune-ups.
- In order to effectively shift, it is suggested to gain speed then relax the force applied to the pedals, shifting, and then maintaining a smooth cadence until the chain is aligned properly before more force is exerted.
- This could be hard on a pedelec system where the rider relaxes the input and the motor goes on pulling hard. In this scenario, it is best to shift on a flat surface where only a small amount of force is needed to keep the bike moving forward.
- The problem here is that shifting is constantly done when you encounter hills or you start from rest; in the same way as a lot of force is needed to keep the speed. In order to make the story short, be gentle when you shift and acknowledge that mid-drive motors pull the same chain that you do as a bike user.
Mid-Drive Systems ConclusionIn the end, you should have some kind of love-hate relationship with mid-drive systems since you get efficiency but miss some of the zip as well as the instant gratification offered by hub motors. They are usually noisier too. A few mid drive systems could feel frustrating and clunky to shift but a few others are actually satisfying when you use them. With this said, the Bosch system and similar high quality offerings should come to mind, that could actually sense that you are trying to shift and softly cut the motor so that you do not put too much stress on the drivetrain. The last advantage of mid-drive systems is that the motor weight is found centrally on the frame in addition to staying low. This will give stability when you ride or lift the e-bike for storage or transport. A disadvantage is that the motor could be susceptible to logs and rocks while travelling using a mid-drive since it is not surrounded by spokes and a wheel in the way that hub motors are. Most mid-drive systems are protected with some metal or plastic casing that could take a few hard hits before you suffer damage.
Another drive system which splits the difference between hub drive and mid drive is the shaft drive. It operates just like an automobile and positions the motor more towards the main part of the bike while you drive the rear wheel using a shaft. These are not quite common today, since they require customized frames which are not symmetrical. A rear wheel drive truck usually has a drive shaft extending from the motor back to the rear wheels which is found under the body, a bicycle has to use one of the chain stay arms in order to support the shaft. This could make it look somewhat out of place and probably hard to service as well.
On the whole, the drive system that you choose is going to impact the total weight and weight distribution of the electric bike. It is going to give more or less efficiency so you could ride fast, navigating or climbing bumps and it is going to cost more or less which depends on how customized the frame is and if it offers regeneration as well as special sensors to shift gears. In general, geared hub motors offer affordable lightweight around town transportation, direct drive hub motors for more silent riding, regenerative braking and increased power and mid drive motors for mountain biking or plenty of hill climbing.
What is a Watt?
A watt is a unit of power. You can determine the wattage of an electric bicycle by taking the voltage and multiplying it by the amps of the battery. They measure the potential output of a machine powered by a battery.
What Wattage Do I Need?
The amount of power you need will depend on your weight and the terrain you will be riding. If you are 120-220 pounds you can get a 300-watt motor. If you are only going to riding flat terrain. If you live in a hilly city like Seattle, San Francisco or Downtown Los Angeles you may want to upgrade to a 36-volt battery that puts out 750 watts of power to climb very steep hills. If you are over 220 pounds a 500-watt bicycle will be sufficient in a flat city but if you want to climb steep hills a 1000 watt bicycle is what you will need to get you up with ease.
How much power do you need? An electric bike with a motor between 250-350 watts can be enough for everyday riding, but if you live in a hilly city, you may need an electric bike with more power to get you up those hills. If you opt to get a less expensive model (under $1,000) the battery will probably be less than 36v and the motor will be less than 500w. This simply means you the electric bike won’t be able to climb steep hills as quickly or traverse great distances without running out of battery. By saving up your money and buying a more expensive bike with better components, you will greatly improve your experience.
The wattage of the motor isn’t the only thing that matters. The placement of the motor makes a big difference with performance. A rear-wheel mounted motor will give you consistent energy no matter what type of terrain you ride across or which gear you’re in. A mid-drive mounted motor will give you more torque when you’re in a lower gear. These styles of motors are best for riding on hills or trails.
Peak Performance vs. Continuous Performance
A bicycle manufacturer may claim a wattage of 300 watts but if you take a closer look you may see they mean continuous performance. For example a bike that has 24 volts and a controller with 15 amps has a 360 peak performance wattage output. The manufacturer may claim that bike has 300 watts of power but, that is at continuous power. The difference between continuous power and peak power is that continuous power essentially means power that a motor could safely handle for an indefinite period of time without overheating or damaging the motor. A “250 watt continuous” motor, basically, could run forever at 250 watts and not overheat but any additional power could cause it to overheat eventually. If the motor is really a 250 watt motor by definition, then running the motor at 251 watts could cause it to overheat eventually. Therefore, manufacturers rate the motor for “continuous power” rather than “peak power”.
Is it just fine for manufacturers to rate electric bike motors this way? It is fine actually, as long as the numbers are accurate. Most of the time “a 250 watt continuous” motor could handle more than 250 watts continuously, meaning that the numerical naming convention is not accurate and misleading. The problem is not about morality because of underrating electric bike specifications. This is one of the rare times that you get more than what you pay for. It is this that puts customers into confusion and makes them have a harder time comparing different motors.
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