This article first appeared in Electric Bike Report in June of 2013. Since then, we’ve made some changes to our motor selection - our Direct-Drive motors are now all High-Torque 6x9 wound, so they run slower (approximately 15mph at 36v or 20mph at 48v), and our Geared Motors have been replaced by a 500w version, (approximately 20mph at 36v or 28mph at 48v). The Direct-Drive is now our Heavy-Duty motor and the Geared motor is our performance motor. The 350w geared motor is available in limited quantities at a significant discount, as they are being discontinued.
Comparing Direct-Drive and Geared Motors
Quieter or more torque? More durable or less drag?
The first set of answers corresponds to direct drive motors: they're quieter, but have less torque, they're more durable, but they're also heavier and drag some, making pedaling less efficient, and their range on a full charge is a little less. Direct drive motors are nearly silent, humming along smoothly. In contrast, geared motors make some whirring noises, but are so light and small they could almost pass for a normal bike hub, and there's almost no drag when pedaling, and though they offer more torque, letting you climb hills quickly and accelerate from stop lights like nameless doped-up ex-racers, the nylon gears can wear out under hard use.
What nylon gears? Direct who? The reason you've got a choice at all is because there are two basic ways to get motor power from the hub to the wheel. Let’s look a little closer:
The Direct Drive Motor
The 500w Direct-Drive motor is simple and robust
The direct drive motor (photo above right) is the simplest: the outer shell of the hub is part of the motor, and has a big ring of strong rare-earth magnets fixed to it. When the motor runs, it drives the wheel directly. That's where your name comes from. This means that the wheel is simply a motor with the shaft fixed in place so that the body of the motor (the outer hub shell, and thus your wheel) spins instead of the shaft. It’s a simple system, but the motor has to be big and heavy to produce enough power - a small motor spinning slowly doesn’t produce enough torque, and the speed you want your wheel to turn at is relatively slow, so the motor needs to be as big as possible to produce torque at low speeds, or else you could add some gears to change that….
The Geared Motor
The 500w Geared motor: light, high-torque, and fast.
The geared motor (below) is a little more complex, but the clever complexity makes it lighter and smaller. Gears are awesome, you already have gearing on your bike - it can turn a bunch of low-torque circles into a few high-torque circles, or the reverse - this is handy if you've got a tiny motor and you want to make it push along a loaded bike, so the motor runs at high speed for efficiency and the gearing slows it down and increases the torque, to push you forward. And just like the gearing on your bike, a ratcheting freewheel lets you coast without drag (in this case from the magnets), but the extra moving parts will eventually wear, just like the gears on a bike will some day crunch and skip and slip, and you'll have to replace them (the nylon gears). And since the gearing is small and designed to make a wheel spin fast, heavier riders and riders with a lot of cargo will have trouble with durability. For people that need a really strong push, special direct-drive trike hubs with the motors wound (using more copper) for higher torque and a lower top speed will make pulling heavier loads a breeze, they’ll go slower, but they’ll give lots of power and should last for many years.
Complete Specifications for E-BikeKit motors
The 500w Geared (left) is smaller and lighter than the heavy-duty more durable Direct-Drive motor (right).