brake disc rotors

acac
acac Posts: 348
edited June 2013 in MTB buying advice
hello all
i was thinking of replaceing my old rotors.
i would some lighter ones how about these.
dos any one know what these are like.
QUAXAR IRIS ULTRALIGHT DISC BRAKE ROTOR
http://www.xcracer.com/shop/viewproduct ... ductid=298

am useing superstar Semi Metallic/Organic pads.
will i still get plenty bit and power.



thanks
play hard ride hard

Comments

  • The Rookie
    The Rookie Posts: 27,812
    The disc design doesn't effect power at all as you are applying the same force to the pads.

    I use alligator on the rear (which are pretty similar) and on the front I use a Hayes which is ever so slightly heavier.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • acac
    acac Posts: 348
    am useing s/s Disc Rotor - Helix Design
    trying to lose bit a weight and one abit bent.
    i heard the design effects the power but i dont know, didnt think that it would
    play hard ride hard
  • spacedog
    spacedog Posts: 97
    The Beginner wrote:
    The disc design doesn't effect power at all as you are applying the same force to the pads.

    I use alligator on the rear (which are pretty similar) and on the front I use a Hayes which is ever so slightly heavier.


    I always thought, simply speaking, more metal means more friction and therefore more braking power. Ok, disc cooling will play a factor too.
  • thelonegroover
    thelonegroover Posts: 1,073
    Seems logical that more surface area would increase friction, thus increase braking. As you say more friction will also increase heat. So there will be a trade off between braking hand heating, depending on slots and holes etc. This is assuming the pad force is a constant.
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  • The Rookie
    The Rookie Posts: 27,812
    Surface area may sound like it would effect friction, but it doesn't.....after all you apply the force and the contact area then only effects force per unit area, but the same force is applied and creates the friction, go back to GCSE physics and you'll spot no area in the standard friction calculation.

    Friction=mu x force (for a solid on a surface mass x gravity) see no area!
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • thelonegroover
    thelonegroover Posts: 1,073
    Yes, thats true for pure friction or the coeficient of friction between the disk and pad. But the area does effect the friction force, the greater the area, the less the force, for the same friction force.
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  • thelonegroover
    thelonegroover Posts: 1,073
    Just to add, in your equation, area is a function of force.
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  • The Rookie
    The Rookie Posts: 27,812
    No, friction is coefficient times force applied, THERE IS NO AREA EFFECT.

    Think about it, if you double the area then you half the force applied per unit of area so you get the same friction - obvious innit!
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • spacedog
    spacedog Posts: 97
    GCSE Physics was a long time ago....
    Does this have something to do with an elephant wearing stilettos or have I got things mixed up?
  • The Rookie
    The Rookie Posts: 27,812
    Long time ago for me as well (well never as I did real exams - O-levels).

    Erm...sort of!
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • thelonegroover
    thelonegroover Posts: 1,073
    The Beginner wrote:
    No, friction is coefficient times force applied, THERE IS NO AREA EFFECT.

    Think about it, if you double the area then you half the force applied per unit of area so you get the same friction - obvious innit!

    It is confusing I know but I think we've just agreed.
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  • The Rookie
    The Rookie Posts: 27,812
    Thelonegroover wrote:
    Yes, thats true for pure friction or the coeficient of friction between the disk and pad. But the area does effect the friction force, the greater the area, the less the force, for the same friction force.
    Reading that again - sort of....friction is the total drag, so i wouldn't have put it how you have there

    The friction drag is independant of area, so a spidery disc creates the same drag as a solid disc.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • Giraffoto
    Giraffoto Posts: 2,078
    Spacedog wrote:
    GCSE Physics was a long time ago....
    Does this have something to do with an elephant wearing stilettos or have I got things mixed up?

    No, that's pressure. Or some bizarre dream that you've had. Friction = coefficient of friction x normal contact force, none of these concerns elephants or their choice of footwear
    Specialized Roubaix Elite 2015
    XM-057 rigid 29er
  • njee20
    njee20 Posts: 9,613
    Physics aside there was a noticeable degradation in brake power using KCNC rotors compared to Avid. Fine on the back, but a lot less bite on the front. Don't really care why but I changed back.

    Not use the Quaxars, but they look like they'll be alright.
  • Kowalski675
    Kowalski675 Posts: 4,412
    Wavy disc shapes came from the motocross world originally (although are now often found on road bikes, as a fashion). The thinking behind their design is that the leading edges of the pattern clean the disc and prevent pad glazing (but also wears pads out more quickly).
  • rapid_donkey
    rapid_donkey Posts: 448
    I replaced my Avid G3CS discs with Hope floating rotors. Main reason was the Avids were really noisy and screechy. The Hopes have eliminated that and also seem a touch more powerful too.
    Superstar also do floating rotors.
    Beware though, there is sometimes clearance issues between the rivets on floating rotors and the forks if you do get some. My Hopes fit straight on fine with a Fox fork.
  • acac
    acac Posts: 348
    hi i got the QUAXAR IRIS ULTRALIGHT DISC BRAKE ROTORs the other day.
    use them yesturday for three hour ride and there was not any less power if any think may have abit more power.
    very pleased with them :D
    play hard ride hard

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