How to Replace a Disc Brake Rotor

How to Replace a Disc Brake Rotor

Rotors are a wear item, like pads but slower. Most riders never think about replacing one until the brakes feel weird, the rotor looks visibly thin, or they bend one badly enough that truing won’t bring it back. This guide walks through replacement for both 6-bolt and centerlock hubs, plus the adapter that lets you run a 6-bolt rotor on a centerlock hub.

When to replace

  1. The rotor is worn out. Measure the braking surface (the outer ring the pads contact) and compare it to an unused part of the rotor (usually the inner spider). If the braking surface has thinned by 0.2-0.3mm or more, replace it. The Loam Goat 5 In 1 Disc Brake Tool has built-in wear gauges for Shimano, SRAM, Magura, and Hope rotors that show you when it’s time to swap.
  2. It’s badly bent. If you’ve tried truing and it’s not coming back, replace it. (see: How to True a Bent Disc Brake Rotor)
  3. You’re sizing up or down. Common rotor sizes are 140, 160, 180, and 203mm. Going up usually gives you more braking power and better heat management, but you’ll likely need a new caliper adapter, and possibly a different caliper, to keep the pads centred over the larger rotor.

Quick wear check without a calliper: drag a paperclip or pick across the braking surface, then off the rotor into the spider. If you can feel a distinct step where the braking surface ends, the surface has worn down. That’s a replacement.

While you’re in there, check the pads. If they’re getting thin, swap them at the same time. (see: How to Replace Your Disc Brake Pads)

Pick the right rotor

Two things to match:

  1. Diameter. Same size as your old rotor, unless you’re deliberately sizing up. If it’s not printed on the rotor, measure the outer diameter.
  2. Hub interface. 6-bolt or centerlock. Look at your hub: six small bolt holes around the disc surface means 6-bolt. A splined central interface means centerlock. They’re not interchangeable without an adapter.

Some rotors are also compound-specific. If the rotor says “resin pads only” or similar, run organic pads only. Sintered pads on a resin-only rotor will glaze the rotor fast.

6-bolt rotors

Tools

  • T25 Torx wrench (most common, sometimes T20 or hex)
  • Torque wrench in the 0-10 Nm range
  • Medium-strength anaerobic thread locker (Loctite 243 or similar)
  • Clean rag and isopropyl alcohol

Removal

  1. Wheel off the bike.
  2. Remove the six rotor bolts. Engage the wrench fully into each bolt head, the recess is shallow and stripping is easy if you’re not careful.
  3. Lift the rotor off the hub.

Installation

  1. If the new bolts came with thread locker already applied (you’ll see a coloured patch on the threads), they’re ready. If they’re bare, add a small amount of anaerobic thread locker to each bolt or to the hub’s threaded holes. Don’t use grease or oil on the threads. Brake heat will wick oil out toward the braking surface and contaminate the pads.
  2. Note the rotation arrow on the rotor (if there is one). Most rotors are designed to spin in one direction. Match the arrow to the direction of wheel rotation. If there’s no arrow, put the side with branding/writing facing out.
  3. Handle the rotor by the spider arms or the inside edge. Skin oils transfer to the braking surface and contaminate the new rotor.
  4. Drop the rotor onto the hub. Line up the holes.
  5. Hand-thread all six bolts. Don’t cross-thread them. If a bolt won’t start easily, back it out and try again.
  6. Tighten the bolts with the wrench until they’re close to but not quite touching the rotor face.
  7. Rotate the rotor clockwise (looking at the disc side) so the leading edge of each rotor hole pulls up against the bolt. This pre-loads the rotor against the bolts in the braking direction, which reduces the chance of the rotor shifting under hard braking.
  8. Hold the rotor in that position and snug the bolts down lightly.
  9. Set your torque wrench to spec (typically 4-6 Nm, check your rotor’s instructions). Tighten in a star pattern: skip across the rotor each time rather than going around the circle. This pulls the rotor down evenly.
  10. Wipe both sides of the braking surface with isopropyl alcohol on a clean rag.

Centerlock rotors

Tools

  • A centerlock lockring tool. The Loam Goat 5 In 1 Disc Brake Tool has a centerlock wrench built in (and it also works on BSA bottom brackets). For splined lockrings (internal teeth) on quick-release hubs you can also use a cassette lockring tool. Thru-axle hubs need a notched-style lockring tool because the axle is too big for the splined tools to fit over.
  • 3/8” ratchet or torque wrench
  • Clean rag and isopropyl alcohol

Removal

  1. Wheel off.
  2. Engage the tool on the lockring. Turn counter-clockwise. Some require real force to break loose.
  3. Pull the rotor off the hub.

Installation

  1. No grease on anything. The splines on a centerlock hub are dry-fit.
  2. Note the rotation arrow on the new rotor. Match it to wheel rotation.
  3. Handle the rotor by the spider only.
  4. Slide it onto the splines.
  5. Hand-thread the lockring on.
  6. Torque to spec, usually around 40 Nm for centerlock. That’s significantly tighter than 6-bolt. By hand on a wrench held 8 inches from the lockring, that’s about 44 lbs of effort.
  7. Wipe both sides of the braking surface with isopropyl alcohol.

6-bolt rotor on a centerlock hub (adapter)

Two adapter styles exist:

  1. The adapter splines onto the hub, and you bolt the 6-bolt rotor onto the adapter. Treat it like a 6-bolt install: thread locker, star pattern, 4-6 Nm. Then thread the lockring onto the adapter and torque to the centerlock spec.
  2. The adapter has its own engagement tabs that mate with the rotor’s bolt holes. Drop the rotor onto the adapter’s tabs, thread the lockring on, torque to spec. No bolts involved.

Either way, finish with the same alcohol wipe.

After installation

Spin the wheel and check for rub. A new rotor is sometimes slightly different from the old one, just from manufacturing tolerances, and your caliper alignment might need a quick touch-up. (see: How to Fix a Rubbing Hydraulic Disc Brake or How to Align Mechanical Disc Brakes)

Then bed the brakes in before your first hard ride. (see: How to Bed In New Brake Pads)

This article is based on Park Tool’s video How to Replace a Disc Brake Rotor.

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