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  1. #1
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    upgrade to bigger rear rotor

    Im upgrading my brakes from avid juicy 3s 180f 160r to avid elixir cr 185f and 185r.

    is there a downside to the rear being bigger from 160 to 185?
    usually the setup i see is the front always a size bigger than the rear

    Thanks in advanced

  2. #2
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    Just like on cars and motorcycles, front brakes do most of the work in hard stopping situations. In a really hard stop most/all of the weight will be on the front wheel. The bigger the rotor the more stopping power because of the lever effect, the force is applied a greater distance from the axle.

    Downside to having a big rotor on the back might be that it would be too easy to lock up the rear wheel.

  3. #3
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    It depends on how much you weigh, how steep the drops are and for how long that you are braking down them as to whether or not you need that larger rotor in the back.

    Otherwise, as stated, you may experience rear lock up issues which could cause a crash.
    fee-fy-fo-fum...

  4. #4
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    Quote Originally Posted by tim0s002
    is there a downside to the rear being bigger from 160 to 185?
    I think downsides would be unnecessary weight (minimal) and somewhat poorer modulation.

    The only positive I see is increased fade resistance if you wanted to routinely drag the rear brake on long downhills to check speed which could be a valid reason to have the rear rotor be larger than the standard 160mm. Not an ideal setup for me though.

  5. #5
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    The others have pretty much....

    hit on it. Way to easy to lock up the rear with a larger rotor in the rear. Since bike brakes don't have a metering valve to split the fluid and force between the front and rear brakes as an automobile does, and even then they still down size the rear brakes. You'r hands are the metering system on your bike. It is difficult to learn to modulate your hands differently from one another. Most people tend to pull both brake levers with the same amount of force. When you do that on a brake set up with the same size rotors front and rear you will likely lock up the rear wheel under moderate to hard braking. Any time you lock up a wheel you've lost control, because traction is control. That's the down side.

    As Clones 123 noted a larger rotor in the rear can be a plus if you tend to drag the rear brake on long down hills to keep speed under control. However this is not a recommended method, as it does lead to over heating the rear brake and heat fade. A larger rotor in the rear can help a bit. However the recommended method of feathering both brakes is more efficient.

    Anyway that's the reason that many setups use a larger rotor up front. The smaller less powerful rotor in the rear helps you keep from locking up the rear. I've even seen lighter riders swap out the 160mm rotor in the rear for a 140mm for a 160/140 set up.

    Your call of course. You can learn to use any set up you like. We even have one misguided soul at the shop that uses a 160 F/180 R set up because he tends to use his rear brake for 90% of his braking. Definitely NOT the recommended braking method, but I guess it works for the way he rides.

    So go ahead and use the 185/185 set up if you want. It'll just take you some time to get used to the extra power and to keep the rear wheel from locking up. I mean lets face it, many XC oriented bikes come stock with a 160/160 set up, and many folks never go to a larger front rotor and do just fine with them. Depends on your riding style. Just depends on how aggressively you ride.

    Good Dirt
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  6. #6
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    thanks for that input. it does seem very logical to use a smaller rear rotor. im pretty light at 130lbs
    i figured since some setup were 160f and 160r, it would be ok for 185f / 185r. when i use the brakes to control speed, i feather both f and r

    im gonna try it out and if i do lock up the rear too much then i could just change the rotor.

  7. #7
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    Squash, a side question if you and the OP doesn't mind.

    Have you seen a F180/R140 combo? What is the results?

  8. #8
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    Quote Originally Posted by tim0s002
    thanks for that input. it does seem very logical to use a smaller rear rotor. im pretty light at 130lbs
    i figured since some setup were 160f and 160r, it would be ok for 185f / 185r. when i use the brakes to control speed, i feather both f and r

    im gonna try it out and if i do lock up the rear too much then i could just change the rotor.
    I am heavier than you, but after smoking the front brake one too many times...I just went 203 F 160 R from 160 F 160 R.

    Cheaper fix as well.

  9. #9
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    Quote Originally Posted by Kaizer
    Squash, a side question if you and the OP doesn't mind.

    Have you seen a F180/R140 combo? What is the results?
    I've been running that setup with Martas on a few different bikes for quite a few years now. It works great for me. It's well balanced (I typically apply the same amount of pressure to both levers), I have plenty of power and I rarely lock the back wheel. My local trails are kind of tight and twisty with a lot of short ups and downs, really no extended downhills to overheat the brakes. I weigh about 170.

    If I were the original poster, I would just increase the size of the front rotor first and see how that works.
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  10. #10
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    There is nothing wrong with front and rear rotors the same size. Lots of bikes are set up that way.
    And 185 in the rear, may, or may not be overkill (some guys run 203/203 just because they are power hungry )
    Even if 185 in the back is more power than you need, it probably won't cause any problems. Too easy to lock up is not a major concern in the rear, and I bet you will still be able to modulate just fine. It will just take a little less hand force than a 160 would, and it really isn't a big difference.

  11. #11
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    i got the 160 rotor kit just incase the 185/185 doesnt work out. some of the trails ive been on does have some extended downhill so the extra stopping power would help (mind u that im pretty much a noob)

    im very curious as to how the 185/185 combo will work out for me, cant wait to get them on.

  12. #12
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    Quote Originally Posted by tim0s002
    i got the 160 rotor kit just incase the 185/185 doesnt work out. some of the trails ive been on does have some extended downhill so the extra stopping power would help (mind u that im pretty much a noob)

    im very curious as to how the 185/185 combo will work out for me, cant wait to get them on.
    I weigh 165. I use 180 in front and 160 in the rear. I drop down some very steep decents for miles at a time. No issues at all with this configuration. Unless you are over 200 pounds or close to it, you probably won't need the 185 in the rear.
    fee-fy-fo-fum...

  13. #13
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    I'm getting ready to reduce the rear rotor size on my 29er. I think the 180 that I installed is too much. I end up locking the rear tire up too much and believe that going down to a 160 rotor will be beneficial.

  14. #14
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    Quote Originally Posted by frdfandc
    I'm getting ready to reduce the rear rotor size on my 29er. I think the 180 that I installed is too much. I end up locking the rear tire up too much and believe that going down to a 160 rotor will be beneficial.
    So what kind of brakes and how much do you weigh?

  15. #15
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    I went downhill 180/160
    I felt the rotor after going down and the rear ended up quite a bit hotter, 160 is less of a heatsink mass.
    I wasn't trying to drag either of brakes and be sure to modulate both and don't overheat or lock up either one, maybe I am too much of a noob and wasn't riding it right.

  16. #16
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    Rotor size

    I run 180/140... and it works well for me. The 140mm rotor is almost able to hide behind the 34T cog on my cassette. It also looks even smaller on a 29er...

  17. #17
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    Quote Originally Posted by PoorCyclist
    I went downhill 180/160
    I felt the rotor after going down and the rear ended up quite a bit hotter, 160 is less of a heatsink mass.
    I wasn't trying to drag either of brakes and be sure to modulate both and don't overheat or lock up either one, maybe I am too much of a noob and wasn't riding it right.
    It was probably hotter because you used it more, not because the size made such a big difference.

  18. #18
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    Quote Originally Posted by Clones123
    So what kind of brakes and how much do you weigh?

    Avid Juicy 7's with Alligator rotors 180mm. I'm approx 170 lbs.

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