eBike Brakes

eBikes are heavier and often go faster than regular bikes. The ability to stop when you need it adds extra demands for the brakes. In this FAQ we will try to cover the most frequently asked questions about eBike brakes.

Terms:

• Brake disc: see rotor.
• Brake pad: The part of the brake that makes contact with the rim or the rotor. These are made of different materials, but typically a resin compound or ceramic metal. Ceramic metal holds up better at high temperatures, but is more expensive, and for daily use resin is adequate for most riders.
• Cable: A wound steel wire that goes from the lever to the caliper on cable-based brake systems.
• Caliper: The part of the brake mechanism that pushes the brake pads against the braking surface. Calipers either employ pistons or a lever (clamp) mechanism.
• Cut-off switch: This is usually a simple magnet inside the brake lever that detects when the lever moves more than a few millimeters, and sends the cut-off signal to the controller to stop the motor.
• Disc brake: A bicycle brake that uses rotors as the braking surface.
• Lever: The lever sits on the handlebars and is pulled to activate the brakes. Levers are either made for cable or hydraulic brakes. On eBikes they usually have an extra cable with a motor cut-off switch.
• Line (brake line): The tube that runs from the brake lever to the brake caliper and contains either oil or a cable.
• Hose: A sealed tube containing mineral oil.
• Hydraulic: A braking system that uses compressed oil to open or close the brakes.
• Piston: Pistons sit inside the hydraulic caliper and push the brake pads onto the braking surface.
• Rim: The outer side/edge of a wheel that sits just next to the tire.
• Rim brake: A bicycle brake that employs a clamp that uses the rim of the wheel as the braking surface.
• Rotor: A metallic disc that is mounted to the side of the wheel, around the central hub, and used for gripping onto when stopping. Usually made of stainless steel. Rotors exist with several different mounting methods requiring compatibility with the wheel hub they are mounted on.

Common brake types:

Disc brakes vs rim brakes

Disc brakes stop the bike by gripping a metal disc that is mounted around the center of the wheel. Commonly, the brake caliper and disc are mounted on the left side of the wheel, but some models can be on both sides. Rim brakes stop the bike by gripping the rim of the wheel using a single caliper that reaches both sides of the wheel.

Pros & cons of disc vs rim brakes

Rim brake pros:

• They are lighter and easier to maintain, and it’s easier to see when the brake pad is not sitting correctly on the rim or needs replacement.
• Gripping the rim at the wheel’s outer rotational point should provide better stopping power, but in practice this is rarely the case.

Rim brake cons:

• They don’t perform as well in wet conditions.
• The brake pads wear out the rim.
• Rim brake pads get hotter and can reach temperatures that may damage the adjacent tires or wheel rim, or cause the brake pad material to become soft and “glaze,” meaning the surface becomes smooth and loses the ability to grip properly.
• The need for a brake caliper to fit on both sides of the wheel also means there is a limit to how wide the wheel can be, as it creates challenges in bike frame designs.
• If the rim gets bent and has a wobble, you often have to sacrifice stopping power by adjusting the brake pads and moving them further from the rim.

Disc brake pros:

• Disc brakes generally provide better stopping power, as the precise caliper design ensures the brake pads are very close to the disc for maximum grip with minimal need for movement.
• They are available with 2 or 4 pistons for increased grip strength.
• The steel brake disc pulls heat away from the brake pads to prevent them from overheating and glazing, while reducing wear on the wheel rims. Stopping power is not affected by a slightly warped or bent rim or rotor.
• They perform better in wet or muddy conditions.

Disc brake cons:

• Disc brake systems are heavier, but that’s hardly a relevant issue on an eBike, as even mountain bikes and racing bikes use them these days.
• They are definitely more expensive.
• Maintenance is more difficult for several reasons. It’s harder to see when the brake pads need replacement without removing the caliper (but you can see it if you know what to look for).
• They have a very low tolerance for misalignments or bent brake discs (but it only causes annoying noises when riding).
• Aligning disc brakes to avoid noises on some models takes a lot of patience and practice.

Hydraulic vs Cable

Most bicycles, especially older ones, rely on cable brakes. It’s a simple system that has been proven for urban use on regular non-electric bikes for decades. Pulling the brake lever pulls on a steel cable that causes the brake calipers to close. Cable brakes are most common on rim brakes, but are also used for cheap disc brakes. Hydraulic brakes use a hose containing oil (typically mineral oil), where pulling the brake lever increases the pressure in the hose and causes the brake calipers to close. Hydraulic brake systems are more commonly used on disc brakes, but can also be found on niche rim brake systems.

Pros and cons of Hydraulic vs Cable

Cable brake pros:

• Cable brakes are generally quite simple to maintain, especially when it comes to rim brakes.
• They are also cheaper.

Cable brake cons:

• Cables are prone to stretching and rust, requiring periodic maintenance to ensure proper function. These adjustments are usually quick and small but should be done regularly to ensure reliable stopping power. Replacing the whole cable is a larger task but only required based on how much it is used or exposed to water.
• The most important limit of cables is that the stopping power relies a lot on the rider’s grip strength.

Hydraulic brake pros:

• Once a hydraulic brake is set up and working, the hydraulic system typically doesn’t need any maintenance for very long periods, as it’s a fully closed air- and water-tight system.
• The way the oil is compressed when braking means that you can stop the bike with very little effort—often one finger on the brake lever is adequate.
• Superior stopping power.

Hydraulic brake cons:

• More expensive than cable systems (but worth it).
• Riders need to learn the behavior and limits of the brakes, as they can be very powerful.
• While maintenance is rare, it has a high level of difficulty that requires special equipment and “bleeding” the brake system to remove air bubbles.

eBike-specific brake types: Safety, Opener vs. Closer switches

eBikes can use regular bicycle brakes, though we would never recommend it. It is important to consider the benefits of eBike-specific brakes, also known as “safety brakes.” A safety brake has an electronic connection that stops the motor when you pull the lever. This makes sense—why would you want the motor to be pushing the bike forwards if you’re trying not to move forwards? The only case where this makes sense is if you want to do a rear-wheel burnout… if you like the smell of burning rubber, the squealing noise, the stained pavement, and wasting money on new tires, while riding around with a motor that’s actively fighting you when you try to stop.

Safety brakes have one major caveat, and it’s the manufacturer’s chosen circuit type, which is either “opener” or “closer.” These terms refer to how the brake lever communicates with the controller, which then tells the motor to stop pushing. Either the circuit gets closed to allow a current (signal) to pass through, or it is interrupted (opened), and these tell the controller that the brakes are being used.

So why is that a problem? Just get the right one! Well… many online bike shops don’t actively tell you which type they have in stock, which they should. Because if you use the wrong type, the bike will think the brake is being used when it isn’t, and think it’s not being used when it is!

Brake rotors and sizes

Rotors usually come in two types: solid or floating. Regular (solid) discs are machined from one piece of stainless steel. “Floating” rotors have an inner and outer part, allowing for improved cooling to prevent the disc from warping under heated usage. Rotors come with different mounting mechanisms. The most common is a 6-point star shape requiring screws, but make sure you get what you need.

The wider the disc brake diameter, the better stopping power you have—or at least that’s according to physics, specifically torque and leverage. Most eBikes use a brake disc diameter of 160mm, 180mm, or 203mm. The size difference is not enough to make a very considerable difference in stopping power, especially since the brake pads aren’t getting bigger. The biggest gain from a wider diameter in these cases is cooling. The bigger brake disc will absorb more heat away from the brake pads, and that will improve braking power, as hot pads generally don’t grip as well as cool ones.

To increase the disc size on your bike, simply replace the disc. But the caliper will need an adapter that moves it outwards from the center axle, and that requires an adapter that’s built for your frame mount and your brake caliper.

A few tips:

Motor cut-off switches have some common easy-to-fix issues.

The fastest way to troubleshoot if the brakes are causing an issue is to simply unplug the cut-off cables on the brakes and see if it changes anything. This will instantly uncover if any electronics issues are caused by brakes.

If your brake lever is not open enough when relaxed (far enough away from the handlebars), the cut-off switch can be permanently engaged and the bike won’t move. This can be caused by not enough oil in the hydraulic brake hose or a too-short brake-line cable, but usually it can be resolved by adjusting a small screw on the brake lever that moves the lever further out. The screw is usually located on the inner side of the brake lever, but it differs from brand to brand.

Motor cut-off switches can be affected by water, incorrectly registering that the brake is in use. Usually, a magnet is used for engaging the switch to reduce the chance of this happening, but it may still occur. If you suspect this is the issue, you need to wipe your brake levers after riding in the rain and/or give them time to dry out.

Placing a throttle or other electronic control unit on your handlebars, too close to the brake lever, can cause the cut-off switch to incorrectly engage. This is caused by parts or wires that are not adequately shielded from electromagnetic interference. Usually, this can be resolved by moving them apart just a few millimeters.

Contamination and cleaning

Don’t touch your brake pads or rotors with your fingers. Don’t get any oils or soaps on them. This will introduce contaminants that will usually just cause a squealing/squeaking noise, but can affect braking power. Water is not a problem.

To clean brake pads or rotors, use a proper bicycle brake-cleaning solvent. If you have issues with squealing brakes even after you clean them, you can try Swiss Stop brake silencer. It’s a graphite-based spray that you apply to the brake pads. Take the pads out, scrub them on sandpaper to remove the outermost layer of contaminants, then apply a thin layer of spray to the pads and let it dry before reassembling the brakes. At first they will not grip very well, but after a few stops they should start to improve and squeak less.

Cleaning disc brake calipers can be done by taking out the pads. Then insert something that is roughly the same thickness as the combined rotor and pads (about 3–4 credit cards, or if you bought the brakes new, they come with a special plastic gadget) and gently squeeze the brake lever to extend the pistons. DO NOT OVEREXTEND THE PISTONS — this can introduce air into the brake line or cause the mineral oil to leak out. Use brake cleaning solvent with an old toothbrush, or Q-tips to clean the inside of the caliper and the sides of the pistons so they can slide in and out freely.

Aligning the caliper to the rotor

If you’re lucky, you can align the caliper by simply loosening it from the frame or adapter enough for it to move, then pulling and holding the brake lever to center it on the rotor, and tightening the caliper mount screws again while you hold the lever. This works on perfectly straight rotors and calipers with a lot of piston movement, like Tektro. If you have Magura, though, the space between the brake pads and rotor is so small that the slightest wobble in your rotor will make alignments tricky and time-consuming. Magura brakes are totally worth it with their 4-piston calipers though!

Keep it cool

Try not to keep your brakes locked after coming to a stop. When hot brake pads are in constant contact with a hot brake rotor, that area will cool down at a different rate than the rest of the rotor, and this can cause the rotor to warp (bend). As soon as you’ve stopped, release the lever so the rotor can cool down evenly.