Electric Assists 101

When you ride around on an electric assist bike, you get a lot of questions from people. Not surprisingly, for many people the crux of the question is, "what am I looking at?" Is that thing it a motor? a battery? both? something else? How does it make the bike go? Do you pedal? Is it always on? Etc.

You don't really need to know any of this stuff to ride around and be perfectly happy. After all, do we all have a solid understanding about how our computers or ovens work? But if you are curious, here is a very basic rundown of how to understand what you're looking at.

Q: "What is that?"

There are three basic parts of any electric assist system:

1. A battery: This is usually a box or oblong object that supplies power to the motor. It's usually squirreled away wherever the bike maker can find some extra space.

2. A motor: Motors turn the energy from the battery into power that you can use to make your bike go up steeper hills with more ease. Bike motors are usually roundish objects located in one of three places on the bike:

  • Front Wheel: Moves the front wheel faster when you add power. Also known as a "Front hub motor," and often confused with a large internal hub.
  • Rear Wheel: Moves the rear wheel faster when you add power. Also known as a "Rear hub motor," and occasionally confused with a large piece of foam packaging that someone surely forgot to remove. The Bullitt (BionX), BodaBoda and Haul a Day have motors on the rear wheel.
  • In the Middle, on the Chain: Moves the chain faster when you add power. Also known as a "Midrive," and often confused with a battery. The MK1, Bullitt (Shimano) and Spicy Curry have motors on the chain.

3. A screen that lets you control the system: If you look at the handlebars of most electric assist bikes, you'll see a screen that lets you control your assist power level, and see a variety of stats about the system. You'll be able to see how much battery you have left, just like on a phone or computer, your speed and other details. Every system has a slightly different set up. Some systems also have a second set of buttons on the handlebar that you can use to control how much assistance you're getting.


Q: "How do you do it? Is it like a motorcycle?"

There are two ways that most electric assist systems take their cue from you.

  • Your Feet: These systems sense how hard you press on the pedals and, combined with the power setting you select on your screen, adds assistance to get more impact out of each pedal. All of the bikes Vie offers use feet-based electric assist systems, aka "pedal assist."
  • Your Hand: You either press a lever or rotate a throttle with your hand when you want power. The throttle has some sensitivity and gives you assistance based on how far you press or rotate the throttle.


Q: "How do you stop the power? Can you bike without it?"

All of the bikes we offer let you turn off the assistance and be in just plain bike mode while still keeping the overall system on. Like your oven -- plugged in but not doing much unless you actually turn on the burners or oven heat.


Q: "Oh, that regenerates all of its energy so you never have to plug it in, right?"

Ah, sadly no. It's true, however, that some systems, including the BionX system on the BodaBodaBullitt (BionX) and Haul a Day bikes we offer has a regeneration mode. That means that you can select a resistance setting while you pedal and help put power back in to the battery. But you will almost certainly still need to charge it on a regular basis. If you're going down a long, big hill, the resistance setting is a nice way to brake rather than squeezing hard for a long time.


Q: "So I can take that up Powell Street, right?"

Maybe. But probably not. There are real power differences to the many kinds of electric assist systems out there. It can feel like comparing apples to oranges to okra when you get into all of the details and try to figure out what's going to work on your hills. If you're ready for more technical data about the torque, amperage and wattage of each system, check out this handy chart we've put together below. We know some of you are eager to graph and model each system to understand whether it'll do what you want it to do. If you're not excited about the idea of a data crunch, Vie has you covered. We've road tested all of the bikes we offer in San Francisco and the East Bay to ensure that the electric assist systems on the bikes we offer will get you around with as much ease or workout as you want. And no matter what, the easiest way to find out if the system is right level of assistance for you is to test ride a bike through our Bike Tasting Menu!




Spicy Curry

Haul a Day



BionX / Shimano


Currie Technologies / Bosch




D500 DV / STePS

U.S. Performance Line

Centerdrive TranzX M15 / US Performance Line


750W / 1,000W


Rear hub motor / Mid-drive






LiMn 48V / 36V
11.6 Ah

LiMn 36V
11 Ah

LiMn 48V 8.8 Ah / LiMn 36V
11 Ah

LiMn 48V
11.6 Ah

LiMn 48V
11.6 Ah


500 W/ 250 W

350 W

350W / 250W

750 W

750 W / 1,000W

Power (nom/peak)

500 W / 418 W

350/500 W

350/500 W


750W/1300W / 1000W

Torque (nom/max)

25 – 50 Nm, 50 Nm

40 / 50 Nm

Very high / 40 / 50 Nm

160 Nm

# Gears

21 / 8 (internal hub)

Continuous (Nuvinci)

8 / 10


Continuous (Nuvinci) / 9

Basic Bike Weight (no accessories or e-assist)

50 lbs

70.5 lbs

55 lbs

33 lbs

53 lbs

Front Brake

Shimano SLX disc brakes

Tektro Hydraulic disc brake

Tektro Hydraulic disc / Shimano Hydraulic disc

Shimano disc brakes

Tektro Hydraulic disc

Rear Brake

Shimano SLX disc brakes

Tektro Hydraulic disc brake

Tektro Hydraulic disc / Shimano Hydraulic disc

Shimano disc brakes

Tektro Hydraulic disc