Regenerative braking is very common on electric cars, and rare on electric bikes. Regen means that the electric motor is used to slow you down when stopping and generating electricity which is fed back into the battery pack which increases your efficiency and increases range. That is how a Prius is able to get almost as good of gas mileage in stop and go traffic around town as it does on the highway. Obviously, the regen braking system offered on electric bikes is much less sophisticated than the ones offered on electric cars. Ebike regen is usually just on or off and has mild stopping power and is used in addition to manual brakes. Usually on an ebike regen happens when you softly apply pressure on the brake handle and you feel the regen brake kick in….compress the brake handle more and the regular brake activates. Variable regen for an ebike where you have variable amounts of regen based on how hard you hit the brake handle does not exist as of this writing.
Regenerative Braking and Efficiency
The efficiency gain of your regen system will largely be dependent on how hilly your riding environment is, and the style in which you ride. Basically: how often do you stop-and-go and how hard do you stop? Regen can add anywhere from 5-20% efficiency but average rider on the average terrain will get about 10% further distance per battery charge.
What about drag?
Regenerative brakes on an ebike create a bit of extra drag, even when not using the brake. This is because the motor is always engaged in an ebike with a regen system, so the motor is always turning even when coasting. This drag is so small its imperceptible when riding. However it does cut down a small bit on the efficiency of the bike. However, the positive effect on efficiency of a regen system, greatly outweighs the small negative effect created by this drag.
Regenerative Braking and Brake Wear
Regenerative braking can drastically reduce your brake wear and also keep your brakes from getting to hot on extended down hills. Also regen never squeaks and has a nice smooth feel to it. Its a nice and liberating feeling to be charging your battery while riding, rather than creating friction and heat with traditional brakes.
Which bikes are capable of adding Regen?
The easiest motor set up to add regen too would be a gearless hub motor. Geared hub motors have freewheels and therefore cannot have regen. Mid drives could possibly have regen but its harder to implement.
How easy is for a manufacturer to provide regenerative brakes?
On a gearless hub motor very easy. Its suprising that manufactures such as Pedego that sale their best selling bikes with direct drive hub motors have not implemented regen. You would think it is expensive and complicated but it is not. It would literally costs these companies less than $10 to implement it, by just changing to a slightly more expensive controller.
How is Regenerative braking implemented?
It is a simple circuit inside an ebike controller. Since the controller on a production bike already has wiring going to the ebrake (all production electric bikes must have an ebrake cut off), it requires no additional outside wires.
Which production electric bikes have regen braking?
With most modern production bikes choosing small geared motors, regen on a production bikes has been rare. The big exception to this is any Bionx powered production ebikes (Ohm, Smart, Grace, Trek, etc)
Although it is very easy for any electric bike with a gearless hub motor to have regen braking, only a few companies have implemented it. However most of the high end bikes with direct drive hub motors have implemented it such as:
What if i want to build my own electric bike with Regen?
It is easy. Just be sure you buy a direct drive hub motor such as the Crystallyte or 9c hub motor, and make sure the controller you buy has regen ability. The easiest way to build a bike with regen is invest in the Bionx kit (read review) which comes stock with regen.
What about variable Regen?
Variable regen is a real sweet spot for an electric bike and is not available yet. Ebike regen is usually a simple on or off.
The one exception to this is the Bionx kit which you can control the amount of variable regen on the dashboard if going down an extended hill. In the above photo you can see four bars of pedal assist, and if you hit the minus key on the dashboard, you can get 4 levels of regen. Pretty sweet. Bionx seems one step away from adding this to the brake lever where you can get different levels of regen depending on how hard you apply the brake. Kudos to Bionx for having the best regen system available for electric bikes.
Here is a video of how the Bionx variable regen works:
Technical testing information about Regenerative Braking
Justin Lemire Elmore, one of the worlds leading ebike engineers, did a great technical test piece on regenerative braking. You can read his findings regarding regen on this thread on endless-sphere.