How to Measure Bike Brakes

Written by jay angel
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How to Measure Bike Brakes
Bike caliper brakes must be measured to ensure proper fit. (brakes image by Tomasz Plawski from

Caliper brakes are the type that have arms that reach around the tire and brake pads that provide the friction that slows the bike down. The brakes are attached to the frame with a single bolt. The brake is measured from the centerline of this bolt to the middle of the pad. This measurement is referred to as the brake's reach. The reach can be compared to a similar measurement on the bike from the middle of the bolt's hole to the middle of where the brake pad will sit. If these two measurements agree, then you have the right-sized brake for the bike.

Skill level:

Things you need

  • Engineer's rule (measurements in mm)
  • Allen wrenches
  • Small crescent wrench

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  1. 1

    Measure your caliper brake using your engineer's ruler from the middle of the mounting bolt to the middle of the brake pad. Take the measurement in millimetres to ensure maximum accuracy.

  2. 2

    Measure your bike using the engineer's ruler from the middle of the brake mounting bolt hole to the middle of the rotor. Ensure that this measurement is also taken in millimetres.

  3. 3

    Adjust your brake pads if the measurements don't agree. Most calipers have an Allen type of adjustment bolt. Use an Allen wrench to adjust these. Older models have a bolt used to adjust the brake shoes. A small crescent wrench can be used to adjust these types of calipers. Move the brake pad so that the measurement to the middle of the pad agrees with the measurement you took in Step 2. Tighten the screw when you are done with the adjustment.

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