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  1. #1
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    What rotor size do I use.

    I have an international standard disc mount on the front and rear of my newly purshased frame. I am new to discs and do not know what size rotor I need. If I buy a set of brakes with everything inclusive will it make things easier for me when I am assembling it. something I can just plug and play.
    When I buy the brakes I'll need some help on how I should put them on.

    see ya
    ionit.

  2. #2
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    Some clarification

    Quote Originally Posted by Ionit
    I have an international standard disc mount on the front and rear of my newly purshased frame. I am new to discs and do not know what size rotor I need. If I buy a set of brakes with everything inclusive will it make things easier for me when I am assembling it. something I can just plug and play.
    When I buy the brakes I'll need some help on how I should put them on.

    see ya
    ionit.

    Rotor size will be dictated by the type of riding you do, your weight, and the specifications dictated by the fork and frame manufacturer. Your ISO mounts on both frame and fork should definitely handle the caliper mounts for brakes with 6 " rotors. Many will even handle 7" rotors. My bike has a low-end Marzocchi fork, and I have 7" rotors front and rear, as I weigh 230+ lbs, and I want the braking power and heat dissipation the larger rotors offer. I would stay away from anything more than 6" if the stanchions on your fork are less than 30 mm. For 8" rotors, your bike and fork should probably be built up as a freeride or downhill rig, as they are built to withstand the punishment and can accommodate the larger brake rotors.

    Again, consult with your frame and fork manufacturers for what they recommend.

    Clyde
    'If Wal-Mart sold parachutes, who would jump?' Frank Havnoonian (quoting his father) Drexel Hill Cyclery

  3. #3
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    Quote Originally Posted by Call_me_Clyde
    Rotor size will be dictated by the type of riding you do, your weight, and the specifications dictated by the fork and frame manufacturer. Your ISO mounts on both frame and fork should definitely handle the caliper mounts for brakes with 6 " rotors. Many will even handle 7" rotors. My bike has a low-end Marzocchi fork, and I have 7" rotors front and rear, as I weigh 230+ lbs, and I want the braking power and heat dissipation the larger rotors offer. I would stay away from anything more than 6" if the stanchions on your fork are less than 30 mm. For 8" rotors, your bike and fork should probably be built up as a freeride or downhill rig, as they are built to withstand the punishment and can accommodate the larger brake rotors.

    Again, consult with your frame and fork manufacturers for what they recommend.

    Clyde
    That fork advice should be taken seriously... I was about to order a brake with a 200mm (roughly 8") front disk, after checking with Fox about the recommended disc sizing for the Float100 (which is not a thin or lightweight fork) I dropped to a 180mm (roughly 7"). Many forks are not equipped to handle the higher torque generated by larger rotors. That said; unless you are a weight weenie I would go as large as you can on the rotors (particularly front) as the increased power (from the increased leverage) is something you will appreciate every time you grab the lever.
    Normally for lightweight XC race bikes the norms are a 140-160 rear rotor and a 160 Front, for crosscountry/all-mountian bikes a 160-180 rear brake and 160-200 (full freeride bikes would be on the upper end of that)

    Hope this helps

  4. #4
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    help with Disc Brake fitting.

    Could I have a clarification on something. You say that the "Rotor size will be dictated by the type of riding you do, your weight, and the specifications dictated by the fork and frame manufacturer". I am 140 lbs and have a FreeRide Specific frame with a cromoly steel rear triangle. So I am not worried about over stressing it. Does this mean I can just forego the "specifications dictated by the frame manufacturer" because I already know it's strong enough and just buy any reasonably strong braking system.
    And how does the calliper adjust to accommodate the different diameter measurement of rotors? Do you have to buy a calliper that coincides properly to the diameter of the rotor? (exp: 160mm rotor needs a 160mm specific calliper.)


    Thanks Grumpy and Call_me_Clyde.

    Ionit.
    Last edited by Ionit; 02-14-2005 at 06:36 PM. Reason: typo

  5. #5
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    Quote Originally Posted by Ionit
    Could I have a clarification on something. You say that the "Rotor size will be dictated by the type of riding you do, your weight, and the specifications dictated by the fork and frame manufacturer". I am 140 lbs and have a FreeRide Specific frame with a cromoly steel rear triangle. So I am not worried about over stressing it. Does this mean I can just forego the "specifications dictated by the frame manufacturer" because I already know it's strong enough and just buy any reasonably strong braking system.
    And how does the calliper adjust to accommodate the different diameter measurement of rotors? Do you have to buy a calliper that coincides properly to the diameter of the rotor? (exp: 160mm rotor needs a 160mm specific calliper.)


    Thanks Grumpy and Call_me_Clyde.

    Ionit.
    As a cromo hardtail your frame will likely allow you to run a larger rear disc than you would want to anyway. Your front rotor size however, may be limited by the fork. (You are about 20% lighter than the average 170lb, but a larger rotor can easily double the brake jack (the force that tries to rip the wheel out of the dropouts when you apply the brake) so I would still follow manufacturers recommendations no matter what you weigh)

    Some brakes use "adaptors" to mount to the IS type disc mounts, in that case you just need the correct adaptor for the specific rotor size you want to run on each wheel.
    Other brakes mount directly to the IS mounts, here you will need the correct caliper to match your rotor choice. Also understand that the front and rear IS mounts are not in the same place in relation to the wheel (rear is 20mm closer to the axle) so, for instance a Hope #3 caliper mounted on the rear is set up for a 160mm disc but the same caliper used in front would require a 180mm disc. It's really not as complicated as it seems you just buy the set up you want for the front or rear specifically, the manufacturer will will match the rotor to the caliper (or adaptor for post mount type calipers) that is required.

  6. #6
    Nouveau Retrogrouch SuperModerator
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    The short answer:
    The rotors come with the caliper when you by the brakes.
    If you have no idea how to mount them on your bike have your LBS do it.
    mtbtires.com
    The trouble with common sense is it is no longer common

  7. #7
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    Excuse me for thread-jacking here, but while we're on the subject of rotor sizes... Is it possible to order an 8" Hayes adaptor for a QR fork? I have a Z1 SL (32mm stanchions) w/ Hayes discs, and would very much like to put on an 8" rotor. I notice Speedgoat's listing for Hayes adaptors has an option that says "... 8" and Psylo Tulio," but I was under the impression that Hayes did not sell 8" adaptors for QR forks...

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