massive disc

stevie the freerider
stevie the freerider Posts: 212
edited December 2007 in MTB workshop & tech
i have just purchest an 8" hdro disc for my hardtail a cannondale chase 2006 as i am going "one brake" for the new year the warenty says that an 8" disc is fine but will it cause any problems in the long run? i am just concerned that it will cause flex or weaken the frame as it is used fo the od flat drop or trials manovers
cheers
stephen hall

Comments

  • supersonic
    supersonic Posts: 82,708
    Should be no problems at all. Actually a SMALLER rotor will flex the frame more!
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  • stevie the freerider
    stevie the freerider Posts: 212
    realy? i wouldnt expect that!!!
    i will deffanatly stick the 8incher on then
    thanks
    stephen hall
  • supersonic
    supersonic Posts: 82,708
    Not many people realise it, but for a given decelleration, smaller rotors input more force into the caliper and therefore the mounts and frame. One way to look at it is this - we all know that larger rotors are more powerful? So for a smaller rotor we need to pump the brake lever harder ie create more clamping force. So if more force is needed to stop the smaller rotor, more will be transferred into the caliper as the rotor tries to resist slowing down. I could show you the maths lol, but I am not that bored at the minute ;-)
    GT ZASKAR CARBON TEAM

    VOODOO CANZO

    Come and see me at https://www.facebook.com/biketyke/
  • Splasher
    Splasher Posts: 1,528
    supersonic wrote:
    Not many people realise it, but for a given decelleration, smaller rotors input more force into the caliper and therefore the mounts and frame. One way to look at it is this - we all know that larger rotors are more powerful? So for a smaller rotor we need to pump the brake lever harder ie create more clamping force. So if more force is needed to stop the smaller rotor, more will be transferred into the caliper as the rotor tries to resist slowing down. I could show you the maths lol, but I am not that bored at the minute ;-)

    Sonic, this is made up science. The rotor does indeed input less force to the caliper for a given deceleration, but since the caliper has been put artificially further away from the centre of rotation by using an adapter, the adapter just does the opposite and acts a lever, increasing the force back to same amount at the frame. In other words, the relationship between the centre of rotation and the frame mount does not change and so for a given torque, the force at the frame is unchanged regardless of the size of the disc.

    However, you can introduce much higher torques with a larger disc and that in turn can introduce much higher forces at the mount and this is where the risk lies. That said a Chase is a string frame so I don't think you'll have a problem.
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