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  1. #1
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    Does Size Matter? Rotor Size that is.......

    I've been using 160mm rotors with my Oro K24s. Recently I borrowed a bike which had 180mm front, 160 rear Avid Elixir CRs and I went flying the first time I applied the brakes hard. Obviously, that wasn't so smart on my part, but it got me to thinking if, at 230lbs, I should be using 180s

    I'm also wondering if there is some relationship to wheel size. Say is it better to have bigger rotors for say, a 650b or 29er or a DH tire? I ride NE technical terrain.

    Thanks
    Bob
    We told you 650b rocks! Riding converted RFX for years!

  2. #2
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    I currently have 160mm rotors w/BB7's. I'm 240#'s & have no trouble stopping but I'm building up a new bike & was thinking of getting larger rotor for the front. I can easily see myself forgetting that firs time & grabbing too hard...

  3. #3
    Nouveau Retrogrouch SuperModerator
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    Quote Originally Posted by Spongebob
    I've been using 160mm rotors with my Oro K24s. Recently I borrowed a bike which had 180mm front, 160 rear Avid Elixir CRs and I went flying the first time I applied the brakes hard. Obviously, that wasn't so smart on my part, but it got me to thinking if, at 230lbs, I should be using 180s

    I'm also wondering if there is some relationship to wheel size. Say is it better to have bigger rotors for say, a 650b or 29er or a DH tire? I ride NE technical terrain.

    Thanks
    Bob
    Yes, it matters.
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  4. #4
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    im 195lbs and ive been overheating my 180mm rotor on a few trails. the lower section opens up and you can pickup some speed, and then it tightens up again and its really scary flying in with no brakes! more than likely putting the 203 back up front.

    you can always death grip a smaller/over heated rotor and your bike will stop.. but if you're running into that problem, its time to step up a size! if your 160's work for you though, no sense going bigger.

    have always had a 160 out back though. takes a lot to cook a rear.

  5. #5
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    160 works fine on my local trails but having 180 in the front might save me elsewhere so prob go that route eventually. Want to get my new bike up n' running then upgrade a few things in the future. Larger fr. rotor is def on the list..

  6. #6
    trail addict
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    160-180 is over 10% increase in the rotor's mechanical advantage, plus you get a little more surface area to dissipate heat... I could definitely get away with a 160 up front for my regular trails, but I really like having the 180 on the front.

    For DH or for heavier riders, size definitely does matter.
    You better just go ahead and drop that seatpost down to the reflector... the trail gets pretty rough down there.

  7. #7
    Bike builder
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    Yes, rotor size definately matters. But depending on your style of riding, you can may be able to get away with it.

    A couple of years ago I bought an XT front disc brake with 160 rotor. It was fine on the local trails but as soon as I took it up into the mountains for some "proper" riding, it became pretty obvious that it was out of its depth on longer downhill trails which needed a lot of heavy braking.

    So I swapped it for a 204mm rotor, and it's totally transformed. Super powerful, and never any fade nor pump.

    So yes, rotor size can make a massive difference.
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  8. #8
    master blaster
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    wouldnt it also depend on the brake unit being used?
    i have a 180 on the front with hayes stroker brakes and on another bike i have a 160 on the front with slx brakes and i find the slx have more grab to them.
    Quote Originally Posted by ISuckAtRiding View Post
    The dude is like 120lbs, tops lol he can run any tires he wants without issues, i'm sure.

  9. #9
    Slowest Rider
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    Definitely

    I had a Hayes 160 mm rotor and at my 250+ lbs, my brakes were COMPLETELY fading on any hill steeper than a driveway. On long descents, I'd need to stop every 500' or so and give my brakes a break, while whiffing up burnt abestos smell. Without breaks for my brakes, the fading was so bad I could pull the brake handles to the bar and have the bike move completely free underneath with no stopping whatsoever.

    I went to Saint 200 mm rotors on my new Heckler and it's a world of difference. I still see some minor fade on fast steep descents over 1000' but waaay better. And overall the braking is much easier, two fingers instead of full paw hard squeeze.

    If you're small, big rotors may not matter. But proportionally, a 200 mm rotor at ~320 lbs (with me, bike, and gear) is like only having a tiny little 100 mm rotor on someone half my size.

    It also depends if you live in Florida or the east coast, or in the big hills of California (like me) or other west coast mountains. When MTB in nearly-flat technical NJ woods for years, I'm not even sure I needed the clincher brakes.

    Incidentally, I find Gaffer pads are great. They last like metallic pads, but like resin pads they don't squeak. I keep a big stock of them and a couple emergency in my pack.
    Last edited by BigLarry; 04-21-2010 at 01:05 PM.
    It's not slow, it's doing more MTB time.

  10. #10
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    Quote Originally Posted by shiggy
    Yes, it matters.
    Not sure if this plain answer helps the poster.

    Spongebob, I think you would find have a slightly larger rotor up front easier for you to manage considering your weight, especially if you have extended steep descents. Your endo close-call was most likely just because you weren't used to the larger rotors on the Elixirs...and/or most likely you're used to slamming on your Oros hard to be able to stop. It's worth the small investment and I'm sure you'll get used to it quickly.

    Veloreality has a great point about the braking system differences though, some brakes just work better than others. I recently got the Elixir CR's and they are great...but need to go back to a 185mm front rotor. You can also consider the pad differences as well, i.e. metallic vs.organic. Not sure about wheel size in relation to need of a larger rotor. I'm curious as well.

  11. #11
    trail addict
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    Quote Originally Posted by veloreality
    wouldnt it also depend on the brake unit being used?
    i have a 180 on the front with hayes stroker brakes and on another bike i have a 160 on the front with slx brakes and i find the slx have more grab to them.
    It can vary from one model to another, but a bigger rotor with model x is still going to have more mechanical advantage than a smaller rotor with model x.
    You better just go ahead and drop that seatpost down to the reflector... the trail gets pretty rough down there.

  12. #12
    mtbr member
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    Spongebob, I think you would find have a slightly larger rotor up front easier for you to manage considering your weight, especially if you have extended steep descents. Your endo close-call was most likely just because you weren't used to the larger rotors on the Elixirs...and/or most likely you're used to slamming on your Oros hard to be able to stop. It's worth the small investment and I'm sure you'll get used to it quickly.

    Veloreality has a great point about the braking system differences though, some brakes just work better than others. I recently got the Elixir CR's and they are great...but need to go back to a 185mm front rotor. You can also consider the pad differences as well, i.e. metallic vs.organic. Not sure about wheel size in relation to need of a larger rotor. I'm curious as well.

    -------------------------------------------------------------------------------------------------------------------------------------------------------
    All excellent points. Great answers with good points. I always thought that my K24 Oro's were good stoppers, but I came from BB7's, so maybe not. One thing's for sure, that Elixir set up was superb and so much better than my Oro set up. Hmmmm.....
    We told you 650b rocks! Riding converted RFX for years!

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