There are two main mass manufactured types of motors you’ll see on electric bikes: The Hub-Drive Motors and The Mid-Drive motors.

Hub-Drive Motors can be front or rear wheel drive. The motor is inside the wheel and it drives the wheel itself

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Mid-Drive motors are in the middle of the frame. The motor drives the chain ring of the bike and through the chain it drives the rear wheel

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Chain ring is the same part you turning when you're pedaling a regular non-electric bike.

Because a Mid-Drive Motor drives the chain ring and not the wheel itself, it takes advantage of your gears in the rear wheel. For example, when you shift down to easier gears, just like on non electric bike it would be easier to pedal, for a Mid-Drive Motor also it becomes easier to drive the rear wheel. This is the major mechanical difference between Mid-Drives and Hub-Drives. The Hub-Drive motors are built into the wheel itself, so no matter which gear you shift to on your regular bike gear shifter, it won't affect the Hub-Drive Motor's performance. The Hub-Drive Motor will still drive the wheel itself, it has no connection to your chain ring, chain or gears.

This however doesn't mean that Mid-Drives are better than Hub-Drives or visa versa. They both have their pros and cons. So let's compare Hub-Drive Motors and Mid-Drives with a little bit of history.

The internet is chock full of articles and opinions on this topic. You will likely hear that Mid-Drive motors are better on hills, are more reliable and are just the way to go. I would look at who is offering that opinion and make your own judgment call on what you experience on both. When we started selling and working on electric bikes in the late 90's, they were primarily Mid-Drives. Panasonic provided the top of the line Mid-Drive motors on the Giant LaFree Lite. However shortly after the Giant Suede-E came out with a new Hub-Drive motor and every other brand available at the time went with this new, more powerful technology. Bosch really brought the Mid-Drive back into the game around 2014, and Shimano, Yamaha and Brose followed suit with excellent offerings. In our opinion there will always be Hub-Drive motors and Mid-Drive motors and reasons to consider both.

Speaking from personal experience, I ride from West Seattle to Ballard and in the last 10 years I have ridden Front Hub, Rear Hub and Mid-Drives of all types. The distance is 25 miles round trip, and no matter the motor, I am making the same time and same approximate level of effort to get to and from work. The output on a Hub-Drive motor definitely feels more aggressive and can have a certain fun factor to it, where as the Mid-Drive definitely feels a lot more like a bicycle, encouraging proper shifting of gears and such. When riding my Mid-Drive bike with a friend on a Hub-Drive motor, I can see the difference on hills and with the wind. Contrary to popular opinion, the Hub-Drive motor goes up the hill faster and with less effort. Same is true for windy conditions. When facing a strong headwind, the Hub-Drive motor can power through it easier than the Mid-Drive. Now, were I not riding and trying to keep up with my friend, I would not notice or care, as the power still feels great. One thing that is certain is that the mid-drive is a more efficient use of power. In general all of the top brands of Mid-Drive motors are about 250w of nominal output. We have found that this is similar in hill climbing to a 500w Hub-Drive motor. Combined with the fact that the Mid-Drive is using your chain and gears, the battery usage is considerably less on a Mid-Drive. This can really be felt on starting from a stop, for example. On a Mid-Drive, you really need to gear down when coming to a stop so that you can have the right amount of pressure and proper cadence when accelerating up to speed. Just like for a human on a non electric bike it would be easier to start pedaling in low gear,  same for the Mid-Drive motor, it's easier to start driving the wheel in low gear. With the hub motor you will likely not be shifting down as much due to the fact that the motor will accelerate faster and get you up to speed quicker.
As for wear on the drive train, while it is true that a mid-drive puts more pressure and causes more wear on your chain and cassette, the fact that you are likely staying in the smaller, high gears on a hub motor will cause the cassette/freewheel to wear out just as quickly.

Hub-Drive motors, however, can accelerate very aggressively, they can afford to do that, because the motor is in the wheel and drives the wheel itself. Mid-Drive motors in general are designed to accelerate smoothly, again because of the way it's designed - if you drive your chain ring very aggressively all of a sudden, you might break the chain. Within the family of Hub Motors, there are two main types:

Geared Hub and Direct Drive Hub Motors.

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The main advantage of a geared hub motor is the ability to freewheel when not in use. This means that there is no drag when coasting. A direct drive hub motor always has a little bit of magnetic drag. This allows for regenerative braking or regenerative modes, throwing voltage back to the battery. Geared Hub Motors can not have regenerative function, (neither do Mid Drives by the way). In our experience though, regeneration on Direct Drive Motors is very minimal, offering 2% to 10% under certain circumstances. It takes a lot of work to pedal the bike with Direct Drive Motor that's been put in regeneration mode. However there are instances where you can get quite a bit charge back into the battery without doing any work. For example by going down the hill that's at least 10 miles. We've had a customer who reported going down 20 miles hill with regenerative mode and putting more than 10% charge back into the battery. Best use of Direct Drive Hub Motor's regenerative feature is probably regenerative brake systems. Brake levers will have integrated sensors that sense when you squeeze the levers and communicates with the controller to put motor into regeneration mode, this helps slow you down through the motor drag. Direct Drive Motors also can take off a little bit quicker than Geared Hub Motors.

Most Hub-Drive motors are manufactured by either the electric bike brand itself that it's attached to or some less known brands that the electric bike manufacturer is working with.

Mid-Drive motor market has more popular names attached to them. Bosch, Shimano, Yamaha and Brose are some of the top quality Mid-Drive motor manufacturers and different brands of electric bike manufacturers will use one of these Mid-Drives on their electric bikes.

When comparing the different brands of Mid-Drive motors, as always, it is important to get out on test rides. The different outputs and torque ratings can be seen below, but they also have different power curves and power profiles that can affect the feel. Of course the bike they are attached to also can greatly impact the overall impression of the motor.

Here are torque setting on most popular Mid-Drive motor models:

Bosch Active Line 40NM
Bosch Active Line Plus 50NM
Bosch Performance Line 65NM
Bosch Performance Line CX Gen 4 75NM

Yamaha PW series 80NM

Shimano E6100 60NM
Shimano E8000 70NM
Shimano EP8 85NM

Brose 1.2E 50NM
Brose 1.2 85NM
Brose 1.3 90NM
Brose 2.1 90NM

A few words about understanding the numbers.

1) There is no 3rd party regulations or independent advisory organization that measures and compares these output numbers.

a) at what speed, cadence or input torque do you get these numbers?
b) what gear ratio is on the bike itself?
c) what is the peak output watts to achieve this?
d) what is the weight of a rider?

2) This can lead to very different experience and feel. Especially in hilly areas like Seattle and with the shift in temperature and wind factors.

You will see many charts and comparisons online, but graphs can easily be manipulated as well.