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  1. #1
    curious noob
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    Brake rotor questions.

    I've been considering getting new brake rotors for my bike, but I have a few concerns.

    First is cooling. I currently run Avid BB5s with 160mm G2 rotors and speed dial 7 levers. I really want to reduce rear end weight, so I'm eyeing the Alligator Cirrus. Will the cirrus cool as well the the G2? I could see it working two ways:

    1. The G2, with more material, will conduct heat better, distribute the heat and heat up slower.
    2. The Cirrus, with less material, will heat up faster, but with a higher surface area:volume ratio, will cool faster, neutralizing the faster heating.

    Secondly, I want to increase power in the front, but don't want to spend a lot of coin or change the front end weight. The 203mm Alligator cirrus rotor weighs the same as the 160mm G2, but according to the math, should provide 30% more stopping power*.
    *Assuming a 15mm braking surface width(w), we get the radius of the rotor(r), and the formula for "leverage" should be (r-w/2).
    My big concern though is again related to heat (sort of). Will such a large rotor with so little material maintain it's true? Will this rotor start wiggling more easily?

    Third, will these "porous" rotors shred my brake pads? Would it be a good idea to run something with bigger pads like a BB7?

    Fourth, is there a reason no one seems to run alligator rotors in spite of their light weight, low cost, and general sexiness?

    Fifth, has engineering school totally corrupted the way I think about these things, or are these sound questions?

    The main reason I want more power in the front is to get into endos more easily, as well as to be able to keep only one finger on the brake when I'm going down a steep slope.

    Thanks.
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  2. #2
    Rub it............
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    1. Larger rotors in size disperse heat much faster, due to the larger diameter. Your #2 way is what it will be.

    2. You are limited to the size by the fork. My best guess is that your max size will be 180/185mm. When switching to a 180mm rotor, you will need a new adapter to make the 180mm rotor work.

    2a. I've been running the Alligator rotors for over a year now, zero warping problems. I even put them on my new 29r build. But I am using the serrated version.- looks like a saw blade.

    3. As long as you properly setup the brake calipers, you should not have any pad problems.

    3a. Yes you should upgrade to the BB7's. They will provide a much better braking experience than the BB5's

    4. I went to the Alligator rotors to stop brake noise. With the stock Avid Roundagon rotors that come with the BB7's and the inherent noise with Juicy 7's, these are my savior - unless the brakes get wet, then its noise anyway. No matter what you do.

    5. Engineering screws up with common sense thinking IMHO, but yes these are some sound questions.

  3. #3
    curious noob
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    Sorry, the first question was not about size. It was a cirrus vs a G2 of the same size.

    I'm running a rockshox reba 20mm axle, and it says on the website that the max rotor size is 210mm.

    Thanks though!
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  4. #4
    Rogue Warrior&Anarchist
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    210mm is the max rotor size made.
    mountain biking is not a crime, so quit giving me dirty looks before I bunnyhop your car

  5. #5
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    You will save about 20 or 30g going from one rotor type to another.......not worth it, and who knows how well they'll work/eat pads when you're done. If you want to save weight there are far more effective ways of doing it.

    What you can do is to improve your existing brake power, and perhaps drop a rotor size in the rear and be able to stick to the same size at the front. I've noticed the Avid G3 rotor has way more power than the G2. I had a set of Juicy ultimates where I swapped to G3 and the difference felt like at least 20% more usable power. You could end up with 6" front and 4" rear, have better brakes than when you started and also lose weight too!!

    If you want the lowest G3 weight then the XX spec rotors with the alloy carrier are 10g/end lighter than stock steel.
    Rimmer - "There's an old human saying - if you talk garbage, expect pain"

  6. #6
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    if you're overheating your brakes, get bigger rotors. brakes are one of your major safety bits on the bike, dont goof around with stuff like that.. stopping is important, more important than 50 grams

    i have the alligator sawblades.. cant complain. they're cheap and quiet.

  7. #7
    curious noob
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    I don't doubt the importance of brakes. They're the component I take the most pride in, really. Right now, I'm thinking I'll do a 203mm Cirrus in the front. It's big so I really can't go wrong with power or heat. If it's a good performer, I'll then try a 160 or a 180 in the back. I figure as long as I'm increasing the size, any loss of relative power will be negligible. Also, I'm running sintered pads so I'm not super worried about eating them. If I do eat them, it will give me an excuse to buy these bb7 calipers off someone I know.

    I've read nothing but good things about the sawblade design, but I like the cirrus because they are "rotationally symmetrical" if that means anything. The braking area has no "bias" in any particular direct, only the supports do. I've been trying to learn to ride backwards and want my brakes to perform the same both ways.

    I do like the sawblade look more though. Having a 203mm sawblade would look genuinely scary.
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  8. #8
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    Ok. I've decided that i'll stick with 180. I talked to some guys at the shop, and they said 180 was a nice improvement and that 203 would just be overkill. Too much power and too likely to get bent up on rocks.
    I'm definitely going to start with the front first before I try anything with the rear. I plan to order an alligator wind cutter, which is the sawblade version. It seems to be relatively popular and have good reviews all around.
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  9. #9
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    Quote Originally Posted by AlexRandall
    You will save about 20 or 30g going from one rotor type to another.......not worth it, and who knows how well they'll work/eat pads when you're done. If you want to save weight there are far more effective ways of doing it.

    What you can do is to improve your existing brake power, and perhaps drop a rotor size in the rear and be able to stick to the same size at the front. I've noticed the Avid G3 rotor has way more power than the G2. I had a set of Juicy ultimates where I swapped to G3 and the difference felt like at least 20% more usable power. You could end up with 6" front and 4" rear, have better brakes than when you started and also lose weight too!!

    If you want the lowest G3 weight then the XX spec rotors with the alloy carrier are 10g/end lighter than stock steel.
    +1 on 120mm back rotor. Most of the actual stopping power is in the front. I have 120mm in the back and it can easily lock. It provides better modulation too and cuts 20-30g.

  10. #10
    curious noob
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    They make 120mms? I thought the smallest they got was 140.
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  11. #11
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    Quote Originally Posted by drbroccoli
    They make 120mms? I thought the smallest they got was 140.
    Me too.

  12. #12
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    Quote Originally Posted by bvibert
    Me too.
    Haha. I was converting from inches to metric and just woke up.
    Yes, 140mm.

  13. #13
    curious noob
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    Would it be possible to mount an IS brake directly to the IS rear mount and create a 120?
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  14. #14
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    Quote Originally Posted by drbroccoli
    Would it be possible to mount an IS brake directly to the IS rear mount and create a 120?
    Good question, assuming someone can make one. I find the 140mm even too strong for the rear.

  15. #15
    curious noob
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    Maybe at that point v-brakes make more sense.
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  16. #16
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    Quote Originally Posted by drbroccoli
    Maybe at that point v-brakes make more sense.
    True...but one nice thing about rotors is that I can run through a stream and I can stop

  17. #17
    curious noob
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    Quote Originally Posted by veritechy
    True...but one nice thing about rotors is that I can run through a stream and I can stop
    Yo dawg, I put a rim in your rim so you can brake while you're wet. /just shoot me now.

    Mount a 20 inch bmx wheel on a specially machined axle parallel to your main wheel....
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  18. #18
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    Quote Originally Posted by drbroccoli
    Yo dawg, I put a rim in your rim so you can brake while you're wet. /just shoot me now.

    Mount a 20 inch bmx wheel on a specially machined axle parallel to your main wheel....
    Hilarious man. What happened to light weight and stuff? I thought you were a weight weenie

  19. #19
    curious noob
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    I'm hardly a weight weenie. Given the choice however, I'd rather have less....
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  20. #20
    curious noob
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    Oh, finally. I ordered the rotor. 180mm. I found that Avid adapters are designed for 185mm. Will I be ok using a shimano 180mm compatible rotor? I'm running post mounts.
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  21. #21
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    Quote Originally Posted by drbroccoli
    Oh, finally. I ordered the rotor. 180mm. I found that Avid adapters are designed for 185mm. Will I be ok using a shimano 180mm compatible rotor? I'm running post mounts.
    Should be ok. I think I have the same setup.

  22. #22
    curious noob
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    Quote Originally Posted by frdfandc
    1. Larger rotors in size disperse heat much faster, due to the larger diameter. Your #2 way is what it will be.

    2. You are limited to the size by the fork. My best guess is that your max size will be 180/185mm. When switching to a 180mm rotor, you will need a new adapter to make the 180mm rotor work.

    2a. I've been running the Alligator rotors for over a year now, zero warping problems. I even put them on my new 29r build. But I am using the serrated version.- looks like a saw blade.

    3. As long as you properly setup the brake calipers, you should not have any pad problems.

    3a. Yes you should upgrade to the BB7's. They will provide a much better braking experience than the BB5's

    4. I went to the Alligator rotors to stop brake noise. With the stock Avid Roundagon rotors that come with the BB7's and the inherent noise with Juicy 7's, these are my savior - unless the brakes get wet, then its noise anyway. No matter what you do.

    5. Engineering screws up with common sense thinking IMHO, but yes these are some sound questions.
    What kind of power do the Alligators offer relative to G2s?
    Science works.

    "Beliefs are what divide people. Doubts unite them."-Sir Peter Ustinov

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