The vast majority of eBikes use a mechanical disc brake system. Mechanical disc brakes are easier to repair and replace, while hydraulic disc brakes provide more stopping power due to the cable configuration.
The only arrangement that makes the drive motor spin fast on an e-bike is the mid-drive arrangement, where the motor drives the bottom bracket through reduction gears. Apart from all the reasons already mentioned, regenerative braking on e-bikes is rare because the electricity costs for charging and e-bike regularly are negligible compared to the other costs of e-bikes, especially purchase, depreciation and maintenance.
Electric bikes are too heavy and powerful for more classic bike brake designs, such as rim brakes or cantilevers, so discs are the way to go. Most quality electric motors spin between 5000 and 20000 RPM, but on e-bikes they don’t spin in that speed range. The drum brake is one of the most common braking systems on ebikes and can be found on the CityGo C7 HMS. I wouldn’t consider buying any ebike with rim brakes and don’t convert any bike you have with rim brakes to electric.
Other electric cars (Tesla) cheat a bit and make the motor braking huge, to avoid having the complicated (expensive and heavy) machinery to adapt between regenerative braking and disc braking when the driver hits the brake pedal. It’s one of the elements that make the Stealth the world’s most durable electric bikes, and the benefits for riders are impressive. In hydraulic setups, you can also find brakes that come with four pistons per caliper instead of the standard two, which are typically seen on some of the higher-end or heavier electric bikes. If this is the case, it’s a good idea to take the bike to your local shop to have it checked out by a bike mechanic.
Other major bike brake manufacturers, such as SRAM and Magura, have also jumped in with their own version of ebike brakes, but Tektro has notably embraced the motorized trend and offers a wide range. Most ebikes come with 160mm or 180mm rotors, but in my opinion, 180mm is the smallest rotor you should consider on the front wheel. Some electric or hybrid-electric cars (Toyota) simulate the typical amount of engine braking with regenerative braking, and at the same time have complicated (expensive and heavy) machinery to adapt between regenerative braking and disc braking using the brake pedal. The cause of this delay (or lack of it on nicer bikes) is the quality and fit of an e-bike’s cadence sensor.
I’ve tested a couple of ebikes with Rim brakes, and even with high quality pads that work decently in optimal conditions, the braking quality degrades so quickly in rain, snow or mud that they are simply no good.