Electric bicycle mid-motor advantages

Mid-drive motors were designed to improve upon a number of shortcomings found in hub motors.

The single largest advantage that mid-motors have over hub motors is their gear ratio. They allow the rider to power the rear wheel via the same chain and gear set as the pedals, which means that a low gear can be selected for powering up steep hills or accelerating from a stop with massive torque. A mid-drive motor in low gear can climb steeper hills than a hub motor of similar power, and can climb hills for longer than a hub motor, which could overheat on long steep hill climbs.

A mid-drive motor is also usually smaller and lighter than a hub motor of similar power. Bafang recently debuted a new line of mid-drive motors for racing bikes that weigh only 5 lbs (2.3 kg). Smaller and lighter mid-drive motors are often stealthier because they can be incorporated directly into the bicycle’s frame. Many people don’t even realize that a mid-motor bike is an electric bike just by looking at it.

Changing a tire on a mid-drive motor e-bike is much easier, since you don’t have a heavy hub motor to deal with. You just change it out like on a normal pedal bike. Plus, since you can use normal bicycle wheels, you have the freedom to use any wheels, tires and cassettes that you wish.

Lastly, mid-drive motors allow the use of true torque sensors for pedal assist systems, which regulate the motor power based on how hard you push on the pedals as measured at the crank. Hub motors often rely on cadence sensors for pedal assist, which only regulate motor speed based on pedal speed, and can cause jerky or awkward motor timing, especially when hill climbing or moving the bicycle around obstacles.

Electric bicycle mid-motor disadvantages

Of course there’s a second side to this coin as well. Mid-drive motors can be brutal on your drive system, which is perhaps their single biggest flaw.

A healthy human can put out 100 W of power for a pretty long time, and 250 W of power during a hard sprint is reasonable. But mid-drive motors can output 250-750 W of power continuously. That’s like having a professional cyclist hammering on your pedals all day. A cheap bicycle chain just doesn’t stand a chance. Snap!

Retail mid-drive e-bikes usually come with upgraded bicycle chains for just that reason, since snapped chains is probably the #1 maintenance issue on mid-drive e-bikes. And because both the motor and pedals need the chain to drive the wheel, riding a mid-motor e-bike with a snapped chain is a strictly downhill affair.

One way to mitigate the chain issue altogether is to choose a mid-drive e-bike with belt drive, though factor the added price into your equation as well.

Because of the increased number of moving parts in a mid-drive motor, there are more points of failure. If the motor does fail, and its a motor that is built directly into the frame of the bicycle, it can be more expensive to replace than just swapping out a hub motor.

In fact, mid-drive motors in general are also more expensive than the tried and true, mass-produced hub motors found on many e-bikes.

There is another downside of mid-drive motors that a lot of people don’t consider until the first time they come to a stop. You can’t shift unless the bicycle is moving (except for bicycles with internally geared rear hubs, which are a minority). That means that if you were in top gear while flying down the street but are then forced to stop at a red light, you’ll want to remember to downshift before coming to a stop. Otherwise you’ll be stuck in top gear when you try to pull away from the light and your acceleration will suffer.

And don’t even think about shifting while under motor power. Doing so is the best way to rip your chain in two. There’s simply too much torque in an electric motor, and the extra stress can easily break the chain when it is between cogs. Nicer mid-drive e-bikes have gear shift interrupters that briefly cut the throttle when you shift gears. But many e-bikes lack this feature, and so it is on the rider to remember to relax the throttle when changing gears. No granny shifting!