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Differences in rotors include size, thickness, pattern cut out of the metal and attachment to the hub. What other differences are their and why? Reason I ask is I recently built up a budget mountain bike and most parts I bought or borrowed from other bikes. One part I borrowed is the discs from another very cheap mountain bike I had (an Apollo) - they seem thicker and heavier than the discs on a Kona Hoss that I have. The brakes on my bike build aren't working brilliantly. Braking is ok but there isn't much modulation. They aren't expensive brakes but they were bought new - Shimano alivio and I'm wondering if the type of discs do play a part?

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  • Some discs have an etched braking surface but can't think of any other differences which would affect braking performance. Have you bedded your brakes in?
    – OraNob
    Jan 26, 2016 at 8:37
  • I've been on 5 25 km rides in muddy wet conditions (Wakerley woods in Northamptonshire, UK) - they are bedded in. The discs are thicker and I wondered if that might be because they are made from cheaper steel.
    – Andrew Welch
    Jan 26, 2016 at 8:39
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    If the disc brake surface is a cheaper polished steel one - you could roughen it with emery cloth. Also you may want to change your pads to sintered metallic pads.
    – OraNob
    Jan 26, 2016 at 8:53
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    Sintered pads would be an option.
    – Andrew Welch
    Jan 26, 2016 at 9:16
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    A clean braking system is important too. Oil + brakes = no good.
    – Batman
    Jan 26, 2016 at 22:50

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There's also the rotor design. There should be holes such that the whole brake pad presses over a void, and several times in the rotation. Some really poor rotors don't have holes arranged right, so one circle of rotor is plain metal the whole way. This doesn't clean the pad and contributes to bad braking.

Thickness is partially to cope with heat. More mass takes longer to heat to extreme levels. Less mass is lighter for riding. Also thicker rotors will resist bending more-so than thinner ones of any quality.

Rotor Size or Diameter is a design thing, not a quality thing. You need the rotor to suit the location of your calipers, and they will depend on the fork mounts and the rating of the fork. Same goes for the ISO 6 bolt holes or for the centerlock style - it is yet another competing standard with relatively minimal effective braking differences.

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  • Interesting regarding the optimal layout of the holes in the discs. Tempting to drill some more holes in it :)
    – Andrew Welch
    Jan 27, 2016 at 8:50
  • @AndrewWelch Don't do that. Your drill could heat the rotor and destroy its tempering (same as a long hard braking session where the rotor goes rainbow-coloured) The rotor will probably be too hard for a normal drill bit anyway. You'd be best off just replacing the rotor with a better one if its not working well enough for you.
    – Criggie ♦
    Jan 27, 2016 at 11:48

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