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  1. #1
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    Why do rim brakes have more power than disks?

    Hello,

    I have a beater old Specialized hot rock kids 05 hardtail and I can easily do endos by just sitting down and pounding the brake when I am going like 3 mph and then I ride my friends GT Avalanche with cable disk brakes and I am not sure what kind they are but in order to endo I have to be going pretty fast and hit the brakes hard while leaning forward and pressing down on the front suspension in order for it to endo a tiny bit. I weigh 82 LBSs and am 4' 9 and also my friends hard rock comp disk is the same way and he does not have hydraulic disks either. I guess this is a disadvantage of disk brakes? or are there some disk brakes (Are hydraulic disks stronger???) that have just as much and more strength than my good 'ol beater rim brakes that same like they have wonderful grab? The back brake pads are toast with almost zero braking power and the pads are off and I only use the front brakes. Is there a smooth, lightweight brake that requires hardly any force to get the wheels to lock up? I dont like having to pull back so hard and it feels like there is so much resistance on the lever. Could someone possibly link me to a brake that requires barely any force to move the lever and is light weight?

    Thanks

  2. #2
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    On a rim brake, its stopping the wheel from the outside, on a disk its stopping it 160mm from the hub. The rim brake has much more leverage. simple.

    and Hydro disks are more powerful, but in clean conditions still dont lock up as well as rim brakes,which is good, in real riding conditions you dont want to lock up.

  3. #3
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    I wouldn't call doing an endo a way to gauge a brakes performance. Those cable disc brakes are probably entry level poo. A good set of hydro's will offer plenty of power and modulation !

  4. #4
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    its pure physics..the further the away from the axle the higher the leverage as power increase proportionally to the lever arm. 13" (26" rim diameter) is about 3 times the distance from 4" ( 8 " rotor diameter). Power up by the same amount.

  5. #5
    Former Bike Wrench
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    A standard MTB rim is actually closer to 23" diameter (22" where the tire bead seats) but otherwise you got the right idea

    Its the tire on a 26x2.1 that is about 26"

  6. #6
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    crappy rim brakes work pretty good, crappy disks are crap.
    Hell is eternally climbing manzanita trail on your singlespeed.

  7. #7
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    Go with hydraulic disc brakes. Just make sure you are using the right ones for what you do.

  8. #8
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    I have no problem doing an endo with one finger on the lever of my 203mm BB7s.

  9. #9
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    OP... i would suspect your buddies' brakes are either; POS's, incorrectly adjusted or somehow contaminated. with that said, the posters above are correct when it comes to leverage - simple matter of physics.
    but my understanding is this; with rim brakes the friction is much less than that of discs. the leverage disadvantage of discs is made up for with higher friction and lever pressure tends to be more linear than progressive [someone please explain this more elegantly].
    all in all, good, well-adjusted disc brakes should be able to send you o.t.b. just as 'easily' as v's
    oh yeah...my bb7 185's-- mucho better than my [adjusted to 'awesome' standards] v-brakes
    Honestly... ahh I give up

  10. #10
    opinionated mechanic
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    Quote Originally Posted by dvng
    its pure physics..the further the away from the axle the higher the leverage as power increase proportionally to the lever arm. 13" (26" rim diameter) is about 3 times the distance from 4" ( 8 " rotor diameter). Power up by the same amount.
    hmmmm...you'd think there'd be more to it than just that. like pad contact area, how the mechanical brake is set up (either disc or v-brake...it makes a difference), the coefficient of friction of the pad compound(s), what levers are being used, etc. a rim brake is not more powerful than a disc brake JUST because the diameter of the braking surface is bigger. w/ proper set up and proper friction between pad and rotor (ie:clean, uncontaminated parts), a disc brake should out perform a v-brake.
    wrenching for a pro team near you soon

  11. #11
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    With a clean rim, clean brake blocks.... a rim brake will probably outperform most discs.
    Gary Fisher Big Sur (custom build) - 2000
    Specialized Pitch Pro - 2008/2009

  12. #12
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    Why are rim brakes not standard on almost any bike over say $500 if they outperform discs? I really don't know, I am just curious.

  13. #13
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    Come and try your rim brakes through a Vancouver winter. I guarantee that on a snowy ride you will have no stopping power, but my discs will work for sure.

    Also, if ease of endo is a sign of power, then the most powerful brake would just be stuffing a good size stick through your spokes. Is that bikerfox posting?

  14. #14
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    Quote Originally Posted by jmw03j
    Why are rim brakes not standard on almost any bike over say $500 if they outperform discs? I really don't know, I am just curious.
    Because

    they are crap when it rains
    if you buckle the wheel they rub
    they damage the rim
    they are not an elegant design solution
    they are not cool
    Gary Fisher Big Sur (custom build) - 2000
    Specialized Pitch Pro - 2008/2009

  15. #15
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    Yeah these suck in snow I was ridin through 8 inches yesterday and it was cold when I got out of the snow I picked up speed and then hit the brakes and absollutely no braking power.

  16. #16
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    v-brakes do create a lot of power, most of which is lost in frame and/or fork flex. and, as other posters have stated, the pads wear your rims, and wet conditions reduce the braking to almost nothing, and everyone loves wearing out pads every other ride in the winter. and on and on and on...
    wrenching for a pro team near you soon

  17. #17
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    i don't think wearing out rim pads is a valid criticsm. they last forever.
    Gary Fisher Big Sur (custom build) - 2000
    Specialized Pitch Pro - 2008/2009

  18. #18
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    Quote Originally Posted by Hand/of/Midas
    On a rim brake, its stopping the wheel from the outside, on a disk its stopping it 160mm from the hub. The rim brake has much more leverage. simple.

    and Hydro disks are more powerful, but in clean conditions still dont lock up as well as rim brakes,which is good, in real riding conditions you dont want to lock up.

    The purpose of this thread has now been accomplished.

  19. #19
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    the internet police have arrived.
    Gary Fisher Big Sur (custom build) - 2000
    Specialized Pitch Pro - 2008/2009

  20. #20
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    Quote Originally Posted by Anno domino
    i don't think wearing out rim pads is a valid criticsm. they last forever.
    I've replaced 2-3 pairs in last winter. You can wear pads in one ride crossing streams when temperature is below the freezing point.

  21. #21
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    The rim brake has a leverage adavatage and no flex from the spokes, but you are comparing a kids bike that probably has a shorter wheelbase and fork.

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