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  1. #1
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    Rotor Size and Grab

    Does the rotor size affect the grab of the brakes? AKA, I have 160mm G2 rotors with Juicy 7's. They are new brakes (maybe 15 miles total). They don't seem to lock the wheels up as compared to my buddy that has J5's with 185mm F/R. Now I am 6'4 and 210lbs, does that matter? Should I get bigger rotors? Or should i just not expect it to lock fully.

  2. #2
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    your pads might need to finish bedding in before you are getting full stopping power. give them a few more miles, but at your weight, it will probably be a good idea to upgrade to 185mm rotors.

  3. #3
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    YOu should be able to lock the back brake fully, but it does sound like they need a little more time to bed in as Call_me_Al stated above

    Find yourself a street with few cars, spin up to 15 mph and do a med pressure stop. Repeat 20 times for organic pads, 30 for sintered. You have to do this for each wheel.

    I agree with Call_me_Al above, a 185 rotor would be good for your weight. Overheating your front on a long downhill is rather scarey
    Lead by my Lefty............... right down the trail, no brakes.

  4. #4
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    I agree with what the others have said above about time to bed in...but how were those 15 miles? Distance doesn't really matter - it's about the terrain. If you're cruising flatland you may need more time to bed in. If those 15 miles were 'hard-on-the-brakes' miles, the bed in should be done.

    For your weight, a 185 up front would be better IMO for steeper stuff.

    To answer your question "Does the rotor size affect the grab of the brakes?" the answer is YES. Bigger rotors have greater leverage - simple as that. They have a larger total surface area as well for more effective heat transfer.

    If after a while, you cant lock the brakes on easy flat land, you may suspect air in the lines - are your levers squishy? If not and they just feel slippy, you may have contaminants on pad/rotor. Clean rotor with Isopropyl and sand the pads and rebed.
    Honestly... ahh I give up

  5. #5
    PCC
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    Larger rotors will allow you to lock up the wheels with less pressure at the levers. It's also true that breaking in your pads will improve the braking power of your existing brakes. If your pads are still breaking in then you may as well upgrade the rotors now anyway as you should break them in to the new rotors when you get them anyway.

  6. #6
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    I'll give it a little more time. I have a brand new 185 sitting around with the front adaptor. the only problem with that is, my front fork is only a dart 2, 100mm fork. it's not "recommended" to go above 160mm

  7. #7
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    Quote Originally Posted by highdelll
    To answer your question "Does the rotor size affect the grab of the brakes?" the answer is YES. Bigger rotors have greater leverage - simple as that. They have a larger total surface area as well for more effective heat transfer.
    Bonus question, if more surface area is better, wouldn't a lower end rotor with less holes be better than an alligator windcutter, or similar rotor with more hole than brake surface?

  8. #8
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    I've been riding J7's for 2 years with 160mm rotors. I rebuilt them and put a 185mm rotor on the front and it made a HUGE difference. Much better modulation, less pressure is required on the lever, and they now stop a lot faster. I usually bed in the rotors on the road but I didn't have time. The first 2 rides were a little scary without much braking power.

    Good luck.

  9. #9
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    Quote Originally Posted by mullet dew
    Bonus question, if more surface area is better, wouldn't a lower end rotor with less holes be better than an alligator windcutter, or similar rotor with more hole than brake surface?
    The surface area matters less than the diameter of the rotor. The surface contact of the pads remains relatively the same whether you are running 160mm or 180mm or 203mm rotors becaue the pad surface area remains constant. The reason you get better braking power from larger rotors is that, by using a larger diameter rotor, you are increasing the leverage that the brake has to act upon the rotating wheel. So, any disk brake can be improved by increasing the rotor diameter but trying to increase the braking power by changing the rotors without increasing the diameter will result in little to no change in braking power.

  10. #10
    ~Disc~Golf~
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    Quote Originally Posted by mullet dew
    Bonus question, if more surface area is better, wouldn't a lower end rotor with less holes be better than an alligator windcutter, or similar rotor with more hole than brake surface?
    To a point..
    More surface area offers better cooling.
    The holes cut weight, help clear pads of mud/water and may aid in preventing 'hydroplaning' (wrong word) from pad out-gassing in extreme temperature situations. Although the latter really only applies to motor vehicles I think.
    Honestly... ahh I give up

  11. #11
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    Quote Originally Posted by SycoCell121
    I'll give it a little more time. I have a brand new 185 sitting around with the front adaptor. the only problem with that is, my front fork is only a dart 2, 100mm fork. it's not "recommended" to go above 160mm
    I would keep the 160 on there then, at least for now.

    If the bed in is not enough, then make sure you are running sintered pads. I'm not sure if they are stock on J7s. They give the most stopping power. Sintered pads usually have a brass looking back plate

    You could also try different 160 rotor. Magura SL Drilled and Hayes wavey rotors both have more surface area to work with vs the G2. Although, as stated above, this will not make a huge difference, but some.

    If neither of these options are working for you, you could try the 185 mm rotor. Be careful here, you could get some weird torque on the fork while riding. This is diffentately one of those "try at your own risk" deals.
    Lead by my Lefty............... right down the trail, no brakes.

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