Let's talk rotor size
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  1. #1
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    Let's talk rotor size

    What are people running these days?

    On my gravel bike i'm 160 front and back but on my road bike I have 160 up front and 140 in the back which I understand is common on road bikes. I read various threads on it and I'm still not sure what optimal is?

    What are the thoughts on why you should run each? I assume it depends on rider weight, how much braking one does and maybe preference?
    Last edited by Trek_5200; 03-07-2019 at 08:05 AM.

  2. #2
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    My guess for the larger rotors on the gravel bike is that it's capable of being used on single track and double track where there could be longer and steeper down hills.

    On the road bike, since the majority of your braking comes from the front wheel, the larger rotor is placed there. Too large of a rotor on the rear will induce too much lock up and reduce modulation. Also, keeping weight down. But I've seen road bikes with 140mm rotors front and rear as well.

    Last thing, you probably won't be able to fit anything larger than a 160 due to frame design and what the frame is capable of handling and braking leverage on the fork.
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  3. #3
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    Best rotor size depends on what you're doing.

    For most people JRA on paved roads, 140 F/R is fine. If you're a larger person 160F/140R...if you're on dirt/gravel roads or touring you will likely want 160F/160R....if you're on a tandem (or DH MTB) you are going to want to scale up 180F or 203F. Bigger rotors allow more modulation and also breaking power (and greater heat capacity) to slow down a larger inertia. Catch being, since larger rotors exert a larger MOI in use, you need heavier built forks.

    ...hence why responsible frame/fork builders specify a maximum rotors size. Use to large a rotor for what the frmaeset is designed for--and you'll find out how poor your dental insurance is.
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  4. #4
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    Quote Originally Posted by Marc View Post
    Best rotor size depends on what you're doing.

    For most people JRA on paved roads, 140 F/R is fine. If you're a larger person 160F/140R...if you're on dirt/gravel roads or touring you will likely want 160F/160R....if you're on a tandem (or DH MTB) you are going to want to scale up 180F or 203F. Bigger rotors allow more modulation and also breaking power (and greater heat capacity) to slow down a larger inertia. Catch being, since larger rotors exert a larger MOI in use, you need heavier built forks.

    ...hence why responsible frame/fork builders specify a maximum rotors size. Use to large a rotor for what the frmaeset is designed for--and you'll find out how poor your dental insurance is.
    funny!

  5. #5
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    Quote Originally Posted by frdfandc View Post
    My guess for the larger rotors on the gravel bike is that it's capable of being used on single track and double track where there could be longer and steeper down hills.

    On the road bike, since the majority of your braking comes from the front wheel, the larger rotor is placed there. Too large of a rotor on the rear will induce too much lock up and reduce modulation. Also, keeping weight down. But I've seen road bikes with 140mm rotors front and rear as well.

    Last thing, you probably won't be able to fit anything larger than a 160 due to frame design and what the frame is capable of handling and braking leverage on the fork.
    sounds like the blended approach is perfect. and i did read it elsewhere. but i also hear some people like 160/160. thanks!

  6. #6
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    I like to run the smallest rotor necessary. On my MTB, I run 180 front and 160 rear for the single track I ride. I'm 220 lbs.

    My wife's gravel bike is setup 160 front and rear which is way plenty for her 110 lbs (shhhhh, don't tell her I mentioned her weight)

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    Quote Originally Posted by JoeDaddio

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  7. #7
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    this post got me thinking . what road bikes support 180. i'm not aware of any

  8. #8
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    Quote Originally Posted by Trek_5200 View Post
    this post got me thinking . what road bikes support 180. i'm not aware of any
    None that I'm aware of either

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    Quote Originally Posted by JoeDaddio

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  9. #9
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    Quote Originally Posted by frdfandc View Post
    None that I'm aware of either

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    Sane here, not aware of any.
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