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  1. #1
    mtbr member
    Join Date
    May 2009

    203mm vs. smaller rotors?

    My '07 Stumpy FSR Comp in XL size has Avid Juicy 5, 203mm/185mm F/R rotors (same rotors on L size). I'm 235 lbs & favorite trail has 33+mph rutted large-rock downhill & long fast downhill section.

    I raced motorcycles long time ago; the Stumpy brakes are the best of anything I've ridden or driven powered or self-propelled. Incredible ability to hold them right before lockup for extended period w/ complete control & confidence. I can still hardly believe how good they are after two seasons of riding.

    Currently shopping for a FS 26 XC for a 650b conversion. Two folks stated my current brake rotor diameters are overkill. Any perceptible downgrade no matter how small would be unnacceptable.

    To what degree might smaller rotors cause any noticable downgrade in performance? I'm guessing it's a virtual certainty, exactly the opposite of the two afforementioned opinions. (The fork on at least one bike on the short list - '07 C'dale Prophet - apparently will not accept larger rotors because of caliper/slider's funny that the same feature than makes the fork work for 650b apparently makes it incompatible w/ larger rotors.)

  2. #2
    Old man on a bike
    Reputation: Bikinfoolferlife's Avatar
    Join Date
    Feb 2004
    Personally I do fine with 185f/160r, but the best way for you to find out is to simply try another rotor size. I tried 203s once and thought they were overkill. YMMV.
    "...the people get the government they deserve..."
    suum quique

  3. #3
    Weekend Warrior
    Reputation: daleksic's Avatar
    Join Date
    Aug 2007
    If you are happy with what you got or are used to I would stick with it. A bigger rotor provides (over same design) better cooling than a smaller rotor. Less brake fade. Also, the area the brake pad passes for every revolution of the wheel is larger (per turn), so you are getting more power than lets say a 140mm or 160mm rotor.

    I run XC and Urban Assaults and i have a 185mm front and 160mm rear and they work just fine (I weigh 190lbs with full gear). I do not do any downhill in Florida.

    I am absolutely certain that the quality of the rotor matters more than the size. I bet that a 160mm G3 rotor will be (in any situation) better than a 203mm Roundagon (the cheap stuff Avid sells). So as you are running avid, i would go with the G3. I understand that Hope, Formula and Shimano have really high quality rotors as well, but I don't know much about them. It's all about dissipating heat. Once it builds up, it heats up your pads and then your brake fluid, causing brake fade and brake failure. The quality of your pads matter as well. I'm not sure if soft Ceramic is the best way to go in your case.

  4. #4
    I think I need to Upgrade
    Reputation: AzSpeedfreek's Avatar
    Join Date
    Feb 2004
    For your size and what you are riding, stick with what you have. It is cheaper, and you are used to it besides Specialized speced the bike like that for a reason and that is that usualy a person riding an XL frame is a bigger person (weight wise) and we(I am 225 without gear) need a bit more braking power than someone that weighs 170 lbs to control our explosive downhill speed retention!!

  5. #5
    squish is good
    Reputation: Clutchman83's Avatar
    Join Date
    Apr 2006
    I think anybody who told you they are overkill is either a weight weenie, hasn't tried a 203mm rotor on the front before, or both. I prefer a 203mm on the front for all conditions. On my trail bike I run a 160mm rotor in the rear for weight consideration and I feel I can achieve better modulation with a smaller rotor. I've run 185mm on the rear and it was really easy to lock up accidentally. I run 203mm front and rear for the DH bike to prevent overheating on the rear but I'd go smaller if it wasn't a concern. At your weight a 203mm is fine, plus Juicy's aren't the strongest brake on the planet so it helps them out in that category.
    Bike good, work bad.

  6. #6
    mtbr member
    Join Date
    May 2009
    Many thanks for the enlightenment...esp concerning differences in rotor quality, something that completely swipped my wittle mind. At least I now know if I get stuck w/ a smaller rotor on the Lefty C'dale, I can upgrade the rotor & other brake components.

    I'm a retired Fire Capt who used to hawk mid-fi to ultra-high-end audio & some video gear on my days off, though I stopped hawking back in 2000 when a FD promotion jumped up the stress level. PM me for questions on the subject/free advice or close to; if I don't know the answers I can get them or refer you to the best forums for advice.

    I met & stood next to Mr. T. at the Consumer Elec Show decades ago...he was helping a vendor fill his display room by standing in the hall, hawking people. I was more interested in the 6' tall Playmate bunnies flanking him but couldn't miss how short was the little mohawk guy...maybe the range of 5-6.

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