A couple of questions about rotor sizing.- Mtbr.com
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  1. #1
    Big Paws on a Puppy!!
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    A couple of questions about rotor sizing.

    Sorry guys for yet another set of dumb questions but can someone please explain what the difference is between an Avid 185mm rotor and other manufacturers 180mm rotors?

    What will the extra 5mm do for me besides a slightly larger diameter rotor?

    Is it just a matter of a larger rotor surface for the brake to grab on to?

    Am I okay to use a 180mm rotor with Avid disc brakes?

    I know I'll need the same sized adapters, I'm just trying to make sense out of the 5mm size difference.

    Thanks in advance for the help!
    ‎"My bicycle masters boardwalk and quagmire with aplomb." - Tom Nuttall

  2. #2
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    What is there to make sense of? What exactly is so difficult? 185 mm is 5 mm larger than 180mm. This means that if you run a 180mm with a 185mm adapter the pad will not make full contact. The pad will wear unevenly. And if the wear is advanced enough, the pads will contact before they will clamp the rotor.

  3. #3
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    Quote Originally Posted by XSL_WiLL
    What is there to make sense of? What exactly is so difficult? 185 mm is 5 mm larger than 180mm. This means that if you run a 180mm with a 185mm adapter the pad will not make full contact. The pad will wear unevenly. And if the wear is advanced enough, the pads will contact before they will clamp the rotor.
    Thanks! I think I got it now.
    ‎"My bicycle masters boardwalk and quagmire with aplomb." - Tom Nuttall

  4. #4
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    if i have a 6 inch rotor can i switch to an 8 inch rotor without cahnging anything

  5. #5
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    Quote Originally Posted by 06fishp
    if i have a 6 inch rotor can i switch to an 8 inch rotor without cahnging anything
    you will need the right adapters for your calipers ... there are many to choose from as seen here
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  6. #6
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    Quote Originally Posted by Ratman
    Sorry guys for yet another set of dumb questions but can someone please explain what the difference is between an Avid 185mm rotor and other manufacturers 180mm rotors?

    What will the extra 5mm do for me besides a slightly larger diameter rotor?

    Is it just a matter of a larger rotor surface for the brake to grab on to?

    Am I okay to use a 180mm rotor with Avid disc brakes?

    I know I'll need the same sized adapters, I'm just trying to make sense out of the 5mm size difference.

    Thanks in advance for the help!
    Yup, pretty simple, Avids rotors are 185mm and most others are 180, and then Hope uses 183's just to make things more interesting!

    The why of it is, who knows!? To make any sense of it at all, you'd have to talk to the folks at Avid. And even then, unless you get really lucky, it's doubtful that the CS techs are likely to know for sure.

    But as XSL_WiLL said, without the sarcasm, and as you noted, you do need to use the correct size adapters for the rotors that you use.

    Good Dirt
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  7. #7
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    Quote Originally Posted by 06fishp
    if i have a 6 inch rotor can i switch to an 8 inch rotor without cahnging anything
    Your first post you want to go from a 6" rotor to a 8" rotor.

    That's a big increase, why do you think you need a 8" rotor ?

    More info.

    What's sort of bike do you have ?
    What brake do you have ?
    What fork do you have ?
    What sort of riding do you do ?

    Fork manufacturers have maximum recommended rotor sizes in the specifications for their different fork models, some forks they only recommend for a 6" rotor, some forks they recommend no bigger then a 7" rotor, some forks it doesn't what size rotor you put on.
    Most fork manufacturers don't seem to recommend putting on a rotor that's larger then 7" if the fork has standard QR dropouts.

  8. #8
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    If you've got a 180setup and get a 185mm rotor then you can shim it out with 2.5mm's of spacers / washers if that helps, been there done that.

  9. #9
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    Quote Originally Posted by cobba
    Your first post you want to go from a 6" rotor to a 8" rotor.

    That's a big increase, why do you think you need a 8" rotor ?

    More info.

    What's sort of bike do you have ?
    What brake do you have ?
    What fork do you have ?
    What sort of riding do you do ?

    Fork manufacturers have maximum recommended rotor sizes in the specifications for their different fork models, some forks they only recommend for a 6" rotor, some forks they recommend no bigger then a 7" rotor, some forks it doesn't what size rotor you put on.
    Most fork manufacturers don't seem to recommend putting on a rotor that's larger then 7" if the fork has standard QR dropouts.



    I have an 06 gary fisher piranha with a monituo axel fork. i do all types of riding from road to dirt jumping

  10. #10
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    My front Alligator is 180mm but I had a 185mm Avid before. Well using a 160mm mount does the trick for this situation. I am not sure if this would work for everyone but it was stated to work for this specific rotor in my searches.
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  11. #11
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    Quote Originally Posted by Mr Pink57
    My front Alligator is 180mm but I had a 185mm Avid before. Well using a 160mm mount does the trick for this situation. I am not sure if this would work for everyone but it was stated to work for this specific rotor in my searches.

    a 160mm rear IS mount is the same as a 180mm front IS Mount thats why it worked.

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