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Thread: 220mm rotors

  1. #1
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    220mm rotors

    Itís 2020, who now has 220mm rotors/adapters on the market? Ordered a new Pivot Switchblade and want to move the 203mm front rotor to the back, and put a 220mm on the front. They are Shimano Centerlock, so would prefer a centerlock rotor rather than using a 6 bolt adapter if possible.

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    Iím not aware of any centerlock 220-225mm rotors available atm. New large rotors like this have actually become available in just the last year, so Iíd expect more options to show up sometime in the nearish future.

    Hope makes a standard, and floating version of their 220mm rotor. Itís a standard 1.8mm thick.

    SRAM makes the centerline in 220mm, and its 2mm thick.

    Trick stuff makes a 223mm rotor, itís 2.05mm thick.

    And TRP makes a 225mm rotor that is 2.3mm thick. This one is too thick to be used with most calipers (TRP makes a special DH brake that uses this thickness rotor that this rotor is compatible with).

    Iíve currently got a 200mm front, and 180mm rear setup. Iíd love to get a new 220mm front rotor, and move the 200mm to the back. I just havenít had a way to easily justify the purchase yet .

  3. #3
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    Formula has one model with centerlock and 220mm, but it's the only one I recall.

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    I like the idea of thicker rotors for heat dissipation but I wonder how thick you can go without getting brake drag, assuming the XTR M9120ís are designed for 1.8mm.

  5. #5
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    Quote Originally Posted by Camstyn View Post
    I like the idea of thicker rotors for heat dissipation but I wonder how thick you can go without getting brake drag, assuming the XTR M9120ís are designed for 1.8mm.
    You are correct. Shimano brakes are designed around a 1.8mm rotor thickness.

    As far as I know, the thicker rotors aren't any better at heat dissipation (how fast they can release heat), but they ARE better at "heat soak" (ie, they have more thermal mass, and can absorb more heat).

    I have a set of TRP Quadiems, which also are designed around the same thickness of rotors. I reached out to their tech support and specifically asked about 2.0mm rotors (the SRAM centerline to be exact). As expected, the 2mm thick rotors may have some clearance issues with new pads. Since pads are a few mm thick, once they are worn in a bit, I doubt you'd notice any difference.

    I doubt the 2.3mm rotors would work with new pads though. Either the pistons wouldn't retract that far into the caliper body and have some serious rotor drag, or the actual track for the rotor in the caliper could be too small (depending on the brake).

    I'm likely to be going to go with the Hope or SRAM rotors if/when I make the change. Mostly due to availability, and the closer to stock thickness.

    Good luck making a decision .

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    Magura has 200ím rotors and PM 170 to 220 adapters available.

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    What forks are you running? Be aware that Fox doesn't warranty for anything over 203mm.

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    FWIW, I think many Rockshox forks are listed as 220mm rotor compatible (I know for sure the Yari and Lyrik are). It is a good callout to make sure that its compatible, before you actually make the switch.

    Also, I think Galfer also has a big rotor available now. Although I've not seen it for sale anywhere off the top of my head.

  9. #9
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    Went with the Hope floating rotor. Iíve heard good things about the Galfer rotors and am familiar with them from my motocross background but my shop carries the Hopes in stock. Itíll be nice when more companies offer the big brakes, Iím surprised they still donít considering how the WC DH guys have been using them for several years already.

  10. #10
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    As a data point-

    I'm 230lbs. I have a custom 29er aggro hardtail with xt 8100 4 pot front brake, 2 pot rear. Stock pads. 200mm XT front rotor, 180 rear. I have local 1700' expert+ fall-line trails, and while i've gotten the brakes HOT, i haven't exceeded their capabilities. That's super impressive; i'm very familiar with overheated brakes. I'm excited about 9" brakes, but while historically they were the next obvious step... now i'm not so sure.
    "Things that are complex are not useful, Things that are useful are simple."
    Mikhail Kalashnikov

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    Itís not just heat, itís also about braking torque.

    Acceleration due to gravity is constant, which means riders of all weights accelerate downhill at the same speed (ignoring rolling resistance and aerodynamic drag). So assuming theyíre at the same skill level (i.e. oneís not dragging the brakes) theyíll both be going the same speed as they approach the same corner in the trail. Theyíll both need the same amount of time to reduce their speed for the turn, which means the deceleration for both riders to hit their entrance speed is the same.

    But!

    The force required to impart that deceleration to both riders is totally different ó*given a constant acceleration, itís linearly proportional to rider weight (F=MA). The 260lb rider needs twice the force as the 130lb rider in order to reduce speed in the same way. That force is produced by the brake calipers squeezing the pads against the rotors. Assuming both riders are running the same brakes, that would require the heavier rider squeeze the brakes twice as hard as the lighter rider (plus some magic brake levers which apply force linearly and some magic brake pads to handle that heat).

    Or the bigger rider could run bigger rotors, which is the moment arm through which the braking torque is turned into braking force. Assuming the riders are running the same calipers, levers, pads, and rotor materials, braking torque is linearly proportional to rotor diameter. So the bigger rider can get a braking torque matched to their body weight by running a rotor thatís twice as big.

    tl;dr A 260lb rider needs 320mm brakes to get the same braking response as a 130lb rider on the same bike.

    Iíve got 220mm rotors front and rear, and it makes a huge difference.

  12. #12
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    Love the mathematical approach! Don't forget, the brakes are there to convert the kinetic energy of the rider + bike to heat & noise during deceleration. Since kinetic energy is 0.5*m*v^2, an increased velocity will increase kinetic energy much more than greater mass. With this in mind, a small rider travelling very quickly can still benefit from these larger rotors. In this case, the smaller rider gets the benefits of the reduced pressure needed for a given torque (saving the hands and arms), but also the benefits of increased heat capacity/dissipation.

    It goes without saying that a big, fast rider should run larger rotors without question.

    Btw I run 223 rotors as well and have tried some thicker (2.3) 246 rotors. They rubbed, but the braking was effortless. These are the future, 100%. Most newer trail forks are 180 post mount standard, so you can run the 223 rotor with an older 160-to-203 adapter.
    MTB scientist guy @ mtbphd.com
    Inventor & founder of BrakeAce

  13. #13
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    Hey mtb_phd, what rotors were these (the 2.3mm x 246mm ones)? Also, how did you attach the 246 rotor? Was that spaced out? What were the forks? I'm quite interested in this setup....

    Cheers

  14. #14
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    The ones I have are Galfer. Used the BrakeAce sensor + a 160-203 spacer to make it work on the Fox 34. Have also used it on a Fox 36 with a 180-203 spacer, but I'm not really sure what either of these forks are rated to.
    220mm rotors-246-galfer-brakeace-bike.jpg220mm rotors-246-galfer-brakeace-close.jpg
    MTB scientist guy @ mtbphd.com
    Inventor & founder of BrakeAce

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