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Thread: rotor size

  1. #1
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    rotor size

    Sort of a cross post.

    I need a new wheelset for my RM Blizzard, so while I'm doing that, I'm gonna switch over to disc brakes as well. Should I go with a 185 front/160 rear combo, or stick with 160's front and back?

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    I'm not convinced the 180 rotor gives you a big advantage if any on an XC bike. I suppose it will dissipate heat a bit better? Initial power shouldn't be any different. Some of it may be marketing as larger rotors look cool in the catalogs, websites and showrooms. For XC work I can't see a problem with 160's F&R. I actually see a bunch of weight weenies on the race circuit using 140mm on the rear. I have 180/160 right now but my bike may see 160mm in the front next year as it is lighter and I can drop the adapter.

  3. #3
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    A 185 rotor will give you about 15% more stopping power assuming the same caliper/pads and effort over a 160 rotor at the cost of slightly greater weight.

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    Quote Originally Posted by waltermitty
    A 185 rotor will give you about 15% more stopping power assuming the same caliper/pads and effort over a 160 rotor at the cost of slightly greater weight.
    How does a larger rotor with the same caliper give you more power? I understand there may be less heat and therefore less fade with a larger rotor but where is the power coming from all things being equal? Leverage?

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    Quote Originally Posted by Tinshield
    How does a larger rotor with the same caliper give you more power? I understand there may be less heat and therefore less fade with a larger rotor but where is the power coming from all things being equal? Leverage?
    leverage

  6. #6
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    Yes. All other being equal 185mm rotor equals 15% higher top braking force due to increased leverage. 203mm rotor will give you another 9% over the 185.

    You are still limited by grip on the front when speaking of the top. However with larger rotor it also takes less force on the lever ( 15% less ) to achieve the same braking force as on 160mm rotor.

  7. #7
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    Excellent info guys thanks.

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    On the RM thread, given the layout of cable stops on this older frame, there's a recomendation to go with mechanical discs instead of hydraulic. No need to dremel out or fabricate hose guides, nor need to cut housing and bleed them to run them through the existing guides. Thinking of going this way, as it's cheap, simple, and I would assume, effective?

  9. #9
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    For what it is worth: I recently switched from 185 to 160 in the front on one of my rides ('09 Turner Sultan w/ ElixrCR) and do not notice much difference. I'm 190# rider 6'2" and most of my riding is XC/trail/someMTN (I do not ride 20+ minute steep downhills very often). I intentionally stopped on downhills before and after for comparison purposes.

    My other ride is still setup w/ 185 F (Fuji Tahoe SL w/ Juicy 7's) and I'm going to do the same. The Fuji's brakes "grab" more and have almost caused endo's on occasion (with no more than 2 fingers on the brake lever at any given time). I could have left 185's on the Sultan but a friend of mine has been after me for a while to lose some weight and give a 160 up front a try.

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