There are a variety of eBikes of every possible make, model, and style on the market. That makes sense, because rider needs and terrain vary. Choice allows you to match the right style of eBike to your needs.
What all eBikes have in common, though, is the need to stop quickly and safely, regardless of the other features. Whether you're braking to control your speed on a steep mountain descent, or making a panic stop to avoid an accident, brakes matter. Better quality eBikes use disc brakes to handle the stopping duties. Unfortunately, some models (typically budget eBikes) are still using obsolete rim brakes. Here's why that's a bad idea.
Rim (caliper) brakes are not sufficient for high-speed eBikes
Modern eBikes are faster and heavier than ever before. Many riders want more range, which means larger batteries. Those larger batteries, in turn, are heavier. More powerful motors add weight, too. Adding a trailer, or cargo to a rear rack? Again, more weight.
It all adds up to a need for much more braking power. The best way to get more braking power is to use a good quality disc brake, especially in combination with an oversize disc brake rotor.
Class III eBikes - those that go up to 28 MPH on pedal assist - can travel much faster than traditional "analog" or "acoustic" bicycles. Faster speeds mean stopping distances are increased, and heavier bikes make it worse.
Rim brakes just aren't up to this task. We've even test ridden some very low quality eBikes with low quality rim brakes that only really slow you down, and don't actually stop at all. Yikes!
Disc brake pads can last far longer than rim brake pads
Bicycle brakes work by creating friction between a brake pad and a rotating surface - a disc brake rotor, or a bicycle rim. If you're traveling faster, more braking force is applied, which in turn wears out the brake pads.
Disc brake pads are typically metal, or a metal / organic hybrid. Rim brake pads, in contrast, are often rubber. Those rubber blocks can wear very quickly. If you're riding an eBike with rim brakes that use rubber brake pads, keep a careful eye on the remaining brake pad thickness. Disc brake pads can typically go much longer in between changes.
Other benefits of disc brakes
On a rim brake system, the brake pad is slowly wearing away the braking surface of the rim (usually aluminum) during normal use. Eventually, over time, the rim will be worn out and require replacement. This happens faster in wet and bad weather, because road grit speeds the wear process.
On a disc brake system, the brake pad runs against a steel brake rotor instead of an aluminum rim. Wear is much, much slower, and when a brake rotor is eventually worn out, replacing it is much less expensive and much less complicated than replacing a rim.
What about mechanical disc brakes?
There are two primary types of disc brakes for bicycles. Hydraulic brakes force fluid through a tube, moving a piston which pushes the brake pad up against the rotor - very similar to a car. Mechanical disc brakes, in contrast, pull a steel cable through a housing, which in turn moves the brake pad.
Most high-end and mid-range eBikes with disc brakes use the hydraulic type, which are generally superior. You'll find mechanical disc brakes on some entry level to mid-range eBikes, generally as a cost savings measure. Mechanical disc brakes can still have plenty of braking power.
Sometimes hydraulic brakes aren't an option - for example, on folding eBikes where the hydraulic line can't be routed through a hinge. In that case, you'll find mechanical disc brakes instead as an alternative.
When you're on a budget, you'll compromise, but your safety isn't one of the features you should compromise on. If budget is limited, choose an eBike with a lower-end drivetrain, or smaller battery, or less expensive tires - just don't compromise on brakes.
Before you buy, make sure the brakes on the model you're considering meet your needs. The vast majority of eBike riders are best served by choosing a bike equipped with disc brakes.