In looking at replacing my disc brake rotors, and looking online I see there are different sizes available (between 180 and 203 mm). My question is, what dimension do I measure on my existing rotor? I'm assuming it's the outside diameter, but just want to be sure.

3 Answers 3


Yep, it's the diameter. Most likey 160mm, but double check. You'll need to get the same size rotors as your old ones unless you get new adapters for your frame.

Also, different manufacturers produce rotors of differing widths. Magura rotors tend to be around 2.0mm, while Avid and Shimano are around 1.8mm.

  • Before you increase disc size you need to check with the frame/fork manufacturer which disc sizes are supported. Most CC frames allow 180mm if not 160mm max.
    – arne
    Commented Feb 21, 2014 at 6:25
  • 2
    +1 for coming back 8 years later to improve the answer.
    – Criggie
    Commented Feb 18, 2022 at 3:56

Note that the thickness of the rotors may differ slightly, so you may have to adjust the brake pads a bit. Also note the difference between bolted and center-lock rotors. Most likely you have a 160 mm 6-bolt rotor though.

  • How do you adjust brake pads? I don't think you can tune them inwards or outwards.
    – NikoNyrh
    Commented Feb 20, 2022 at 14:37

You will need to replace your rotor with the same size as you already have. It is normally stamped on the rotor, the most common size is 160mm

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