XCL rear rotor max size- Mtbr.com
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  1. #1
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    XCL rear rotor max size

    Does anyone know the max size that the XCL can take on the rear? I've been running an 8" front and 6" rear, but my rear is really tweaked. I'm not sure if it got warped from heat, or bent from loading it in my truck. I tried to straighten it out with pliars, and then hammering it out, but it's still a bit off.

    I am considering ordering a larger size, but just want to make sure something bigger will fit. Thanks!

    I've been using Formula Oro K18's if that helps.

  2. #2
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    xcl

    Hey,


    ride on my xcl a rohloff speedhub with a 8" rotor. Itīs closely but i had no problems.





    Quote Originally Posted by Scottandhisdog
    Does anyone know the max size that the XCL can take on the rear? I've been running an 8" front and 6" rear, but my rear is really tweaked. I'm not sure if it got warped from heat, or bent from loading it in my truck. I tried to straighten it out with pliars, and then hammering it out, but it's still a bit off.

    I am considering ordering a larger size, but just want to make sure something bigger will fit. Thanks!

    I've been using Formula Oro K18's if that helps.

  3. #3
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    185mm is as big as you can go.

  4. #4
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    185 mm on mine... you might be able to get a 203 in there. Wait til CHUMBAevo or MotoMatt chimes in for the straight scoop.

    Oh BTW I find getting the rear wheel back in with the bigger rotor can take some patience.
    Work is the curse of the biking classes.

  5. #5
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    Quote Originally Posted by neilster1
    185mm is as big as you can go.
    That's what I thought. I wonder how much a difference I'd notice going with the 7" vs the 6"?

  6. #6
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    Quote Originally Posted by chucko58
    185 mm on mine... you might be able to get a 203 in there. Wait til CHUMBAevo or MotoMatt chimes in for the straight scoop.

    Oh BTW I find getting the rear wheel back in with the bigger rotor can take some patience.
    Thanks, I think that the 180mm should be fine. There really shouldn't be a weight penalty between the 160 and 180mm.

    Now I have to decide between organic and sintered pads. Any suggestions?

  7. #7
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    organics wear faster but aren't as noisy as sintered pads. I consider any noise my brakes make as a warning to spiders and squirrels to get the %^&* out of the way!

  8. #8
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    sintered for better bite and power, organic for quieter ride and (sometimes) better modulation

  9. #9
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    According to Chainreactioncycles webpage, the organics offer more power.
    I've heard of people using different pads in the same caliper to get some benefits of each. Personally, I don't like that idea because they dissipate heat differently, and will wear the rotor unevenly.

    http://www.chainreactioncycles.com/M...?ModelID=17212

    Genuine Formula disc brake pads for the Oro caliper. Qrganic compound offers superior braking power and dissipates heat better than sintered pads, reducing the chance of brake fade.

  10. #10
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    Rohloff on an XCL?

    Quote Originally Posted by sukram
    Hey,


    ride on my xcl a rohloff speedhub with a 8" rotor. Itīs closely but i had no problems.
    So, How do you like that Rohloff on your XCL? Any problem making it work? I am seriously considering one next X-mas since I am SICK and F'ing tired of shearing off derailleurs and hangers . I am on my 3rd one this year and last year I trashed 3 derailleurs and hangers. I would be curious if you had any fit up issues on your XCL? Thanks!

  11. #11
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    On a small XCL its best to use a 160mm
    on a med, and large 185mm,

  12. #12
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    do you really need that much rear braking power?
    I'd go with 120 if they were available.
    I do run 203 on the front, where it matters.

  13. #13
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    if you could run a 120 in the back, I don't see why you need 203 in the front. rear matters for hauling down your back end from speed and there is a reason why it is always the same size or only one smaller than the front. Anything else feels unbalanced to me.

  14. #14
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    I run 160 in the rear and 203 in the front on my XCL and It feels really good. I do most of my braking with the front brake and this set up works really well. I had a 140 on the rear of my Ellsworth and it never felt right. I couldn't imagine having anything smaller than that on the rear.

  15. #15
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    I ordered the 185, so I will post up when I have it mounted if there is a noticeable difference. It should be quieter than the howling rotor on there now!

  16. #16
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    Quote Originally Posted by crazylax42
    if you could run a 120 in the back, I don't see why you need 203 in the front. rear matters for hauling down your back end from speed and there is a reason why it is always the same size or only one smaller than the front. Anything else feels unbalanced to me.
    If your bike is 20' long with low cg maybe, but on normal bike the front brake does over 2/3 of the braking.
    I run 203f/160r and applying same pressure on the levers the rear locks up way before the front.

  17. #17
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    Does it really give you more power, or does it just cool better so there's less chance of warping? I guess that grabbing the wheel further out has the mechanical advantage of being able to apply more torque to slow the wheel. I am not a physicist, so take that with a grain of salt, but I do know that a larger rotor has more metal in it, so it cools better...I previously raced cars...but now I supply the motor.

    Will a 7"rotor lock up quicker than a 6"? I think that MythBusters needs to investigate this.

    Actually, along that line, does a larger rotor adversely affect the horst link suspension? If it is able to generate more force, then will it lessen it's ability to remain active under braking? I would like to hear from the Chumba Engineers on this one.

  18. #18
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    Scott, I believe the bigger rotor has several advantages. First, there is a longer lever arm, so the same amount of pressure on the pads produces more braking torque. Second, the speed of the rotor surface past the pads is larger by the same proportion, and more speed means higher friction drag, all else being equal. So braking force (short of lockup) actually increases as the square of diameter. To put it another way, you need less pressure on the brake lever to achieve the same braking force. I guess you could interpret this as saying the 7" rotor locks up sooner than the 6".

    One of my buddies who is a backyard race car engineer also points out that all else being equal, a bigger rotor allows more precise modulation. So you'd have better control over the lockup point.

    Third, as you point out, the larger surface area can shed heat better. And this is also a square-law effect.

    I don't know enough about bike suspension to speculate on the effects of more brake torque on the Horst link.
    Work is the curse of the biking classes.

  19. #19
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    Nice answer Chucko!

    I will still need to compare to see if I can actually tell the difference. I can feel the modulation on the front with the 8" rotor, but I also thought that it could be from the Formulas vs Hayes that I used to run.

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