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  1. #1
    PCC
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    Is there such a thing as too much braking power?

    My buddy has been on an upgrade binge on his brakes for the past few months now. His bike is a GT i-Drive 5 4.0 that originally came with Tektro Auriga hydraulic brakes with 160mm rotors. Since buying this bike he's upgraded the rotors, first to 185mm front then to 185mm rear. He just put a 210mm front rotor on his bike and, to break this new rotor in, a new Shimano BR-M765 Deore XT hydraulic brake set this past weekend. I've started the break-in process by riding to the top of the closest hill and dragging the brakes all the way down then riding to the top again and doing it again because he did a really long road bike ride the day before and he didn't want to climb that hill. He still needs to finish bedding in the new brake pads but now he's talking about upgrading the rear brake rotor to a 203mm, too. I think that he would try 220mm rotors if he could find an adapter for it. Is this too much? I keep telling him that he should just try this new setup out on the dirt and see how it does before changing anything else but he keeps insisting that he needs a 203mm rear rotor. Yesterday, I was telling him that the Deore XT hydraulic disc brakes are some of the best brakes available right now and that he's already running the largest rotors that, I feel, that he should be running and that, maybe, he should drop back down to 185s.

    He weighs about 200 lbs in full riding gear and his bike is about 30 lbs. We ride long-travel trail bikes more than anything else, so, I believe, his brakes are overkill. Way overkill.

    Thoughts?

  2. #2
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    Probably overkill. What's his reasoning?

  3. #3
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    The only thing more over kill, would be a stick in the front spokes at high speed

  4. #4
    PCC
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    I think what had happened was that the Tektros didn't have any real braking power so he kept upgrading the rotors thinking that more is better. The problem is that the Shimanos are going to be so much better than the Tektros that the larger brake rotors are just bringing it over the top, in my opinion. He hasn't actually ridden the bike since doing the last upgrade and the pads still have not fully bedded in, yet, so he just thinks that the new brakes will be about the same as his old brakes.

  5. #5
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    I guess this means you get cheap 'used' parts for your bike.....

  6. #6
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    Rotors that big probably aren't necessary but they won't hurt him unless he really sucks at modulating brakes. There's trade-offs with everything including larger rotors. The most obvious is that they're heavier, but they're also more flexy laterally and I kinda think they look wrong - especially those Shimano rotors with their narrow brake tract.

  7. #7
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    I just upgraded to a Shimano XT 203mm front rotor, which I use together with XT M775 calipers and levers. Just mounted the rotor and took the bike out for a spin today. The stopping power at the front is just incredible! I still have the 160mm rotor at the back and that works great! Anything bigger would be just mad.

    If he still thinks he need more stopping power, why not try out a 4 piston caliper, like the new Shinamo Saint, Hayes Stroker Ace or Hope Tech M4. Just a thought
    Mosso TI frame, RockShox REBA Team fork, Shimano XT package, XTR M975 wheels w/centerlock discs, Xpedo TI pedals.

  8. #8
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    I run formula k24's 200/180mm and i am 225lbs and ride quite agressively including some technical descents and these are very good and controlable with excellent modulation.
    He might also want to check his forks are warrantied and suitable to run these large rotors.
    I would have thought a 200mm on the rear would be wasted due to only limited rear braking.

  9. #9
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    8" rear does have a use - dragging your brakes on a long downhill to prevent overheating fronts. I can't think of a better use besides that though....

  10. #10
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    I could be wrong but I dont think dragging the brakes is how you bed new brakes, I think you are supposed to make several/many hard stops as you go down the hill and NOT drag the brakes.... I believe dragging the brakes will end up glazing the pads and cause you to end up with less power.


    Quote Originally Posted by PCC
    My buddy has been on an upgrade binge on his brakes for the past few months now. His bike is a GT i-Drive 5 4.0 that originally came with Tektro Auriga hydraulic brakes with 160mm rotors. Since buying this bike he's upgraded the rotors, first to 185mm front then to 185mm rear. He just put a 210mm front rotor on his bike and, to break this new rotor in, a new Shimano BR-M765 Deore XT hydraulic brake set this past weekend. I've started the break-in process by riding to the top of the closest hill and dragging the brakes all the way down then riding to the top again and doing it again because he did a really long road bike ride the day before and he didn't want to climb that hill. He still needs to finish bedding in the new brake pads but now he's talking about upgrading the rear brake rotor to a 203mm, too. I think that he would try 220mm rotors if he could find an adapter for it. Is this too much? I keep telling him that he should just try this new setup out on the dirt and see how it does before changing anything else but he keeps insisting that he needs a 203mm rear rotor. Yesterday, I was telling him that the Deore XT hydraulic disc brakes are some of the best brakes available right now and that he's already running the largest rotors that, I feel, that he should be running and that, maybe, he should drop back down to 185s.

    He weighs about 200 lbs in full riding gear and his bike is about 30 lbs. We ride long-travel trail bikes more than anything else, so, I believe, his brakes are overkill. Way overkill.

    Thoughts?

  11. #11
    PCC
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    WRT to bedding the pads in, the first pass was more like a series of gravity-assisted stops. That hill is about a mile long and the descent is about 200 vertical feet. On the second pass I did longer stops as there are a few stopsigns between the top and the bottom and I stopped at each stopsign.

    He actually likes the look of the large brake rotors. The front fork is a Fox 32 Vanilla RLC. He looked it up and, it appears, the 203 front rotor is okay with Fox. Anything larger, though, is not.

    WRT to cheap parts, so far I've only benefitted from a 185 IS to post adapter and a 185mm rotor but neither of these will work on my bike, which has older Hope Mono-Minis which are IS. I stuck those parts onto my son's bike that has BB-7s. Speaking of more braking power, I'm hoping to upgrade my brakes to 185s both front and rear on my bike.

  12. #12
    squish is good
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    I am a big proponent of a 203mm rotor front, 160mm rear for aggressive trail riding but a 203 is straight up overkill on the rear. I have one on my DH bike and it's a hairsbreath from nothing to locked. You're buddy needs to care less about how it looks and think more about having effective modulation. I agree that 160mm rotors on the front result in severe arm pump on just about any trail (that I would call fun at least ) so the big rotor makes sense there.
    Bike good, work bad.

  13. #13
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    Quote Originally Posted by vk45de
    8" rear does have a use - dragging your brakes on a long downhill to prevent overheating fronts. I can't think of a better use besides that though....
    That is why I like 8's. Better heat dissipation. I also setup for one finger braking and the extra power of the 8 reduces how hard I have to squeeze with one finger.

  14. #14
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    It sounds like your buddy is just on an upgrade binge, so he is not likely to listen to even the soundest of reasoning. The best you can do is just nod and smile.

    That said, he is almost certainly wasting his money. A larger rotor isn't going to stop you any faster in most situations, as your limiting factor is going to be traction, not lack of brake torque. A larger rotor provides only a relatively small amount of additional brake torque, and if a given rotor size is already capable of locking the wheel, additional torque is of no benefit. Mostly what a larger rotor provides is additional surface area and mass for quicker cooling during extremely heavy use, which seems unlikely on a relatively low-end fs bike... If he isn't regularly fading his 160mm rotors, he isn't going to stop any faster with 203's.

  15. #15
    "El Whatever"
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    Two words for your pal... MAGURA GUSTAV

    If that doesn't cut it for him, please report back. I'll be rolling on the floor laughing my arse off if he tries the Gustavs and find them not quite enough.
    Check my Site

  16. #16
    GO JIMMIE!!
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    Quote Originally Posted by Warp
    Two words for your pal... MAGURA GUSTAV

    If that doesn't cut it for him, please report back. I'll be rolling on the floor laughing my arse off if he tries the Gustavs and find them not quite enough.
    Or the old Shimano XT 4 Pots...
    My Bike: '03 Specialized HardRock FrankenBike
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  17. #17
    PCC
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    Sorry, folks, he won't be upgrading his brakes to Maguras any time soon as he's barely had his brand new Deore XT brakes for a week, now.

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