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  1. #1
    aka Tom Reingold noglider's Avatar
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    What makes dual-pivot brakes work so well?

    I asked the most experienced mechanic at the bike shop what makes dual pivot sidepull brakes work so well. His quick snide comeback was, "They have double the pivots!"

    It looks, by the design, that it has more leverage, but then the lever might have half the leverage. The amount of travel at the lever is about the same. So what makes them stop better?

    A more general question: what good is improving the leverage of a brake caliper? V-brakes clearly have a lot more leverage, because the end of the arm, where we attach the cable, is very far from the fulcrum. But to counteract this, we use levers that have LESS leverage. Are we back to where we started? Or is this inherently better in practical use?
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    Another interesting fact is that the pivots are not symetrical so each pad travels in a different path. IMHO what makes them good is that the travel between each of the arms is mechanically linked and don't depend on a perfectly balanced spring to keep them centered allowing manufacturers to use weaker return springs which in turn requires less pressure on the levers to overcome.

  3. #3
    slow as I ever was Ex Pres's Avatar
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    Q1: Pivot point is closer to the brake shoe? (Just a shot in the dark), along with the arm between the shoe and the pivot being more straight (as compared to SP)
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    coprolite fietsbob's Avatar
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    I see only1 pivot is close to the shoe, on my on hand example, the other one is still the center,
    or other 2 , since there are 3 parts involved.
    the spring is just connected to one arm, but still spreads the 2 apart.

    Aero brake levers certainly have more leverage, compared to pre aero types.

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    aka Tom Reingold noglider's Avatar
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    Are you sure they have more leverage? Do the shoes move less for a given amount of lever travel at the handlebar? I guess I'll measure, next chance I get.
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    Quote Originally Posted by noglider View Post
    Are you sure they have more leverage?
    Yes.

    Do the shoes move less for a given amount of lever travel at the handlebar?
    Yes, but that's OK because they don't rely on a spring for centering which allows for tighter pad to rim clearances.

    Mechanical advantage is about 4:1 with conventional side-pull brakes and levers versus 5.6:1 for dual-pivots.

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    coprolite fietsbob's Avatar
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    It's really noticeable, I split up a set of single pivot Campag Record brakes.
    †he caliper remained on my RB1, I got Shimano Aero levers and put them on..

    the Pre Aero lever went on my SA drum brake bike , Mustache bars,
    the lower leverage pulls the kind of cable those need ..

    A second set went on my Cross Bike, the difference in the High Leverage Shimano
    on the end of the cable, and the lower leverage of the top mount brake lever ,
    in the middle of the same cable, results in a balancing act being adjusted for,
    to make them work at all well together.

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    I find myself wondering why dual pivot calipers aren't used everywhere. Linear pull/v-brakes are a pain to set up and adjust, and in my experience they hardly ever work well for any length of time. Their action relies on 2 separate spring-loaded arms that have to be 'balanced' and that balance never seems to be stable.
    Last edited by jim hughes; 08-19-11 at 03:13 PM.

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    Quote Originally Posted by jim hughes View Post
    I find myself wondering why dual pivot calipers aren't used everywhere. Linear pull/v-brakes are a pain to set up and adjust, and in my experience they hardly ever work well for any length of time. Their action relies on 2 separate spring-loaded arms that have to be 'balanced' and that balance never seems to be stable.
    Tire clearance, and a good set of V-brakes can be very powerful.

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    leverage....nope...having stiff caliper arms, good pads, and good cables and housing... improves the performance of brakes.

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    noglider, I'm no expert, but I think it's because instead of two arms pivoting from the caliper mount bolt's area there's only one. The second pivot point has a much shorter arm to the brake pad which increases the entire brake's mechanical advantage. Mechanically they're otherwise similar to single pivots, cable on one arm and housing on the other pulling the two arms (squeezing?) together when actuated.

    Close? (I kinda think you actually know.)

    Brad
    Last edited by bradtx; 08-19-11 at 04:38 PM. Reason: sp

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    Constant tinkerer FastJake's Avatar
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    Quote Originally Posted by jim hughes View Post
    I find myself wondering why dual pivot calipers aren't used everywhere. Linear pull/v-brakes are a pain to set up and adjust, and in my experience they hardly ever work well for any length of time. Their action relies on 2 separate spring-loaded arms that have to be 'balanced' and that balance never seems to be stable.
    You're either working with crap components or don't know how to set them up. I admit traditional cantis can be a pain, but V-brakes are probably the easiest to setup IMO and offer more power than any other type of rim brake. As mentioned, they also provide more tire clearance than most calipers.

    Quote Originally Posted by merlin55 View Post
    leverage....nope...having stiff caliper arms, good pads, and good cables and housing... improves the performance of brakes.
    Yes, but all things being equal a dual pivot will feel better and produce more powerful braking than a single pivot. I have a few bikes around the time Shimano switched from single pivot to dual (1990?) Even with everything else the same, the dual pivots are just better. That's not to say that perfectly good braking can't be achieved from a single pivot though.
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  13. #13
    Senior Member BCRider's Avatar
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    Merlin, on two of my older bikes with long reach single pivots I switched to dualies. No other changes to cables, housing or levers. The difference from the singles to the duals was like night and day. It's far more than the rest of the bits in the system. So it all comes down to the leverage ratio.

    The things like stiffer arms and better cables and housings helps a little. But the primary advantage of the duals is that there's just more pressure at the pad face for the same amount of lever effort.

    If someone made a single pivot that worked with standard levers but had the same leverage ratio as the dualies then this new single pivot design would fee the same. But to do that the arms would be sticking WAY out to the side by the amount that provides that jump from roughly 4:1 to 5.6:1 noted by Drew above. The location of the interarm pivot on the dualies give us the longer effective arm length without the arms sticking out to the side by so far.
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    biked well well biked's Avatar
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    Here's a couple of photos of one of my bikes (at different times with different tires, cables, etc) with the same '09 Campy Centaur group on it, complete with the Campy skeleton brakes. The rear brake is a single pivot, the front brake is a dual pivot. Campy's reasoning for putting a single pivot on the rear is that it will be less likely to lock up the wheel, and a bonus is that it saves a little weight.

    Hopefully, these photos will provide a good visual example of the two brake types, especially since they're from the same component group. I don't know why one is more powerful than the other from an engineering perspective, but apparently there is a difference because Campy put the single pivot on the rear using the logic that the single pivot brake would make it less likely to lock up the rear wheel.

    I do know I had bikes with single pivot sidepull brakes from years ago, and the main problem I had is that they were a pain to keep centered. As long as the rims were aluminum, the bikes stopped pretty well. Like most modern road caliper brakes, these Centaur brakes, even the rear single pivot, have a centering adjustment screw to keep the spring tension balanced and the brake centered, so even the single pivot brake stays centered.

    Dual pivot front:



    Single pivot rear:

    Last edited by well biked; 08-19-11 at 06:59 PM.

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    Senior Member BCRider's Avatar
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    Those pictures really shows the difference in the cable arm lengths. The effective arm length on the front is from the interarm pivot while the rear is from the single center pivot.

    On the front caliper the fixed pivot is a floating pivot which also connects the brake to the bike. But it's the free floating interarm pivot which determines the leverage ratio.
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  16. #16
    don't try this at home. rm -rf's Avatar
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    I have the same brakes. I never thought about how they get more leverage, so I took off the wheel and looked up from the bottom of the brakes.

    The right side pivot is bolted to a fixed arm, the piece behind the two pivoting arms. The left arm that is attached by the center bolt has a cam that is pushed up when the right side arm is pulled. So the long right side arm also helps to move the left side! Ingenious!

    The cam is the part to the right of the center bolt, that you can see through the gap in the split right side arm. It rests on a lip near the right side bolt.





    You can see the centering/adjusting screw is at the cam here:

    Last edited by rm -rf; 08-19-11 at 07:13 PM.

  17. #17
    Senior Member BCRider's Avatar
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    My bad! You're right, both pivots are fixed and the outer arm moves the other side with a pin that engages the stub from the rear arm where it extends towards the outer arm's pivot bolt.
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  18. #18
    aka Tom Reingold noglider's Avatar
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    OK, thanks, folks. The caliper of dual pivots is found to provide better leverage. If I used one of those calipers and used a low-leverage lever on the handlebar, would it feel like an old fashioned single pivot?

    My problem with V-brakes is that they work so well. A good V-brake doesn't go out of adjustment quickly. You do have to move the pads as they wear, but the balance of spring pressure doesn't change much over time if it's a good quality brake. Why is this a problem? Well, I think they're ugly, and I could dismiss them as a bad idea if they worked badly, but they don't, so I can't.

    I built a Surly Cross Check up for myself, and I had a choice between old fashioned cantilevers and V-brakes. V-brakes stop better, but I chose old cantis, because I love them, and they look so cool.

    My old 1982 McLean has Campy Record single-pivot brakes. I have strong hands, so they stop great for me. I just have to squeeze hard. But not everyone wants to, and that's OK.
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    Someone likes cantis? I've had few experiences with them that didn't end in wanting to throw them at something.

  20. #20
    aka Tom Reingold noglider's Avatar
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    I know, they take a long time to set up. But I'm a bike mechanic. I'm patient, and with my experience, it takes me less time than it takes other people.
    You don't read my signature anyway, do you?

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    Quote Originally Posted by noglider View Post
    OK, thanks, folks. The caliper of dual pivots is found to provide better leverage. If I used one of those calipers and used a low-leverage lever on the handlebar, would it feel like an old fashioned single pivot?

    My problem with V-brakes is that they work so well. A good V-brake doesn't go out of adjustment quickly. You do have to move the pads as they wear, but the balance of spring pressure doesn't change much over time if it's a good quality brake. Why is this a problem? Well, I think they're ugly, and I could dismiss them as a bad idea if they worked badly, but they don't, so I can't.

    I built a Surly Cross Check up for myself, and I had a choice between old fashioned cantilevers and V-brakes. V-brakes stop better, but I chose old cantis, because I love them, and they look so cool.

    My old 1982 McLean has Campy Record single-pivot brakes. I have strong hands, so they stop great for me. I just have to squeeze hard. But not everyone wants to, and that's OK.
    One of my bikes has 600 DP calipers operated by SunTour GPX levers and braking power is less than another bike with 105 DP calipers and matching brake levers. Better than braking performance of any SP caliper set (last was a set of Cane Creek SL200) I've had, YMMV.

    Brad

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    I think dual pivots work well because the arms are shorter than single pivot and most modern dual pivots are strongly made using forging. Both of these add to stiffness which makes all the difference in braking.
    Mechanical advantage is something you can play with in design, eg cable pull at the brakes and leverage at the arms, but I dont think you can add much power to hand braking.

    My cantilever brakes suffer from bending in the cable stop. A stiffer stop would improve the system a lot but I cant get one that fits. My steel stop has a long drop so I can bend the cable.

  23. #23
    AEO
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    Quote Originally Posted by Nerull View Post
    Someone likes cantis? I've had few experiences with them that didn't end in wanting to throw them at something.
    The most annoying thing about canti brakes is not the tediousness of setting up them up properly or how they protrude outside of the frame.

    It's that after all that work, if your work was too good, they can shudder, because of their ridiculous mounting method. If the brake pads grip well enough to bend the fork, then the brakes will grab even harder, then the brakes will slip and the fork will be sprung back until the pads grip again and the whole cycle will repeat itself until you let go of the brakes. Even a crown mounted cable stop is no guarantee to stop this, so it's a flawed design from the start.

    I've had this happen on a 1-1/4" fisher evo size fork and that was annoying enough for me to slap on V-brakes for that bike.

    If you must design a mission critical component, such as brakes, make sure that frame integrity won't affect the operation of it. plain and simple rule that cantis violate.
    Last edited by AEO; 08-20-11 at 05:33 AM.
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    Quote Originally Posted by AEO View Post
    The most annoying thing about canti brakes is not the tediousness of setting up them up properly or how they protrude outside of the frame.

    It's that after all that work, if your work was too good, they can shudder, because of their ridiculous mounting method. If the brake pads grip well enough to bend the fork, then the brakes will grab even harder, then the brakes will slip and the fork will be sprung back until the pads grip again and the whole cycle will repeat itself until you let go of the brakes. Even a crown mounted cable stop is no guarantee to stop this, so it's a flawed design from the start.
    I have a Surly Cross check with Shimano's BR-R550 cantis. Due to the straddle cable design and the fact they use V-brake type cartridge pads, set up, adjustment and pad alignment isn't very difficult or tedious. Certainly far better and easier than the LX cantis I had on a '92 Trek MTB.

    Their stopping power with the OEM pads was decent and somewhat better with Kool Stop Salmon replacements but not as low effort as any of my other road bikes with dp side pulls.

    They do have a tendency to squeal that comes and goes. Toeing in the pads reduces it for a time but it eventually returns and that alone has had me contemplating V-brakes and the required lever change.

  25. #25
    AEO
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    Quote Originally Posted by HillRider View Post
    I have a Surly Cross check with Shimano's BR-R550 cantis. Due to the straddle cable design and the fact they use V-brake type cartridge pads, set up, adjustment and pad alignment isn't very difficult or tedious. Certainly far better and easier than the LX cantis I had on a '92 Trek MTB.

    Their stopping power with the OEM pads was decent and somewhat better with Kool Stop Salmon replacements but not as low effort as any of my other road bikes with dp side pulls.

    They do have a tendency to squeal that comes and goes. Toeing in the pads reduces it for a time but it eventually returns and that alone has had me contemplating V-brakes and the required lever change.
    no, no, the thing is, cantis just aren't designed correctly to begin with and some combinations just won't work at all without shuddering, no matter how much they are adjusted. I've literally tried different pads, toe-in levels, and even makes of cantis, but this one fork I could not get to stop shuddering.
    Food for thought: if you aren't dead by 2050, you and your entire family will be within a few years from starvation. Now that is a cruel gift to leave for your offspring. ;)
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