E-MTB brake rotors

How to choose a brake rotor for your electric mountain bike

An electric mountain bike weighs 22 to 26 kg and descends just as fast as a non-electric mountain bike: the rotor absorbs much more energy each time you brake and dissipates it as heat. Manufacturers address this with thicker, larger rotors, sometimes incorporating the speed sensor magnet.

2 mm thick instead of 1.8 mm

• E-bike brake rotors can be as thick as 2 mm — Galfer Wave, Magura MDR-P — versus the standard 1.8 mm: more material means greater thermal mass and less warping when hot.
• Check that the piston clearance accommodates this thickness: a 2 mm rotor reduces the available clearance accordingly.
• Magura MDR-P combines an aluminium body with a steel braking surface to dissipate heat faster; MDR-C is a one-piece steel rotor, simpler and cheaper.

203 mm is becoming the norm

On a trail or enduro electric mountain bike, 203 mm has become the standard at the front, and many bikes also use 203 mm at the rear. Moving from a 180 mm to a 203 mm rotor requires a caliper adapter, and you need to check the maximum rotor diameter permitted by both the fork and the frame.

The speed sensor magnet

Shimano brake rotors RT-EM300, RT-EM600, RT-EM810, RT-EM910 and RT-CL900 are available with an integrated magnet that replaces the spoke magnet for the STEPS speed sensor. There are two variants: a standard magnet, or an external magnet for remote sensors. If your bike reads speed from the rotor, replacing it means choosing exactly the same variant — otherwise the assistance will no longer be regulated correctly and the display will show an error.

Center Lock or 6-bolt

• Centre Lock : splined fitting and lockring, quick to install, predominant on Shimano hubs.
• 6-bolt : six Torx bolts, predominant on Magura, SRAM and Hope hubs.
• Center Lock to 6-bolt adapters are available; the reverse is much rarer.
• Some Magura brake rotors are available with matching brake pads — a pairing designed to work together, useful when replacing both.

To find out more: How to maintain your electric mountain bike

See also: Electric mountain bike speed sensors · E-bike brake pads · Mountain bike disc brake adapters