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  1. #1
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    Larger vs. smaller brake pad surface area ?

    The surface area on my current disc brake pads seems quite small (maybe the size of a nickel) I was looking @ a few other brake sets and they appeared closer to a quarter. What effect does larger or smaller surface area have on brake performance ?

  2. #2
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    All other things equal, a bigger pad would increase braking performance just as a larger rotor would. Difference in caliper designs definitely play a role too, though.
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  3. #3
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    Bwahahahahahahahahahahahahaha!

    Don't listen to him, Keen. Changes in the surface area of the pad affect the pressure of the pad upon the rotor, thus the amount of friction. Your question is much more complex than it would seem, and you can't reach any general conclusions from just that one bit of data.

  4. #4
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    Quote Originally Posted by RustyIron
    Bwahahahahahahahahahahahahaha!

    Don't listen to him, Keen. Changes in the surface area of the pad affect the pressure of the pad upon the rotor, thus the amount of friction. Your question is much more complex than it would seem, and you can't reach any general conclusions from just that one bit of data.
    So, don't listen to what, genius? Been baking in the socal sun a bit long?
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    Quote Originally Posted by RustyIron
    Bwahahahahahahahahahahahahaha!

    Don't listen to him, Keen. Changes in the surface area of the pad affect the pressure of the pad upon the rotor, thus the amount of friction. Your question is much more complex than it would seem, and you can't reach any general conclusions from just that one bit of data.
    Maybe you could elaborate and shed some light on the complexity ?

  6. #6
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    Quote Originally Posted by Bikinfoolferlife
    So, don't listen to what, genius?

    Don't listen to YOU.

    "Bigger pads, larger rotors."
    What does THAT mean?

    'Spose you just tell us about the relationships between area, pressure and friction.

    Bwahahahahahahaha!
    Dummy!

  7. #7
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    Quote Originally Posted by keen
    Maybe you could elaborate and shed some light on the complexity ?
    Sorry, Keen. There is insufficient data to reach any meaningful conclusion. But perhaps we can still help. Specifically, what brake components are you considering installing, and what is your desired goal in changing from your current setup?

  8. #8
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    Quote Originally Posted by RustyIron
    Sorry, Keen. There is insufficient data to reach any meaningful conclusion. But perhaps we can still help. Specifically, what brake components are you considering installing, and what is your desired goal in changing from your current setup?
    I currently run Hayes Mag brakes w/ G1 Calipers. I like the brakes but the calipers are quite dated. The new Hayes Stroker Trail calipers can be used w/ my Mag levers, according to Hayes. The calipers have the same diameter pistons but the Strokers have larger pads.

  9. #9
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    Quote Originally Posted by RustyIron
    Changes in the surface area of the pad affect the pressure of the pad upon the rotor, thus the amount of friction.
    You're wrong. All else being equal, you're right that there will be less pressure on the rotor with bigger pads, since the force from the pistons will be spread out over a greater area. However, this doesn't translate to more friction. Friction is proportional to the FORCE applied, not the pressure. So if you run pads made from the same material in the same brakes, power wouldn't change. The smaller pad would wear faster, and would not dissipate heat as well. But that's it.


    If you're going to spout off and call someone out on something, at least make damn sure you're right.

  10. #10
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    Quote Originally Posted by RustyIron
    Don't listen to YOU.

    "Bigger pads, larger rotors."
    What does THAT mean?

    'Spose you just tell us about the relationships between area, pressure and friction.

    Bwahahahahahahaha!
    Dummy!
    Heat is a large factor in a disc brake's performance. A larger pad can dissipate heat better, as can a larger rotor (which also has a torque advantage). That's what it means. Go back to your physics class and figure it out...
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  11. #11
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    Quote Originally Posted by Hardtails Are Better
    So if you run pads made from the same material in the same brakes, power wouldn't change. The smaller pad would wear faster, and would not dissipate heat as well. But that's it.
    I wouldn't be too sure about that. Why you suppose they put wider tires on sports cars? To not change friction at all?

  12. #12
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    Quote Originally Posted by vk45de
    I wouldn't be too sure about that. Why you suppose they put wider tires on sports cars? To not change friction at all?
    The contact area does not change the coefficient of friction. But a larger contact area means just that... more contact... This can help account for uneveness, bumps, etc.

  13. #13
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    Small pads generate more heat per unit of pad surface, so they use a broader range of operating temperatures. Pads can't be designed to be optimal at all temperatures, but can be designed to be effective at high temps or low temps. Larger pads allow the designer to select a pad that operates more powerfully in a narrower range of temps or have more consistent performance at a wider range of temps.
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  14. #14
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    Quote Originally Posted by XSL_WiLL
    The contact area does not change the coefficient of friction. But a larger contact area means just that... more contact... This can help account for uneveness, bumps, etc.
    Actually, this is wrong.

    Quote Originally Posted by wikipedia
    The force of friction is independent of the apparent area of contact. (Amontons' 2nd Law) (Amontons' 2nd Law does not work for elastic, deformable materials. For example, wider tires on cars provide more traction than narrow tires for a given vehicle mass because of surface deformation of the tire)

  15. #15
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    Not exactly wrong...

    The force of friction is independent of the apparent area of contact (in an ideal world)... The contact area does not change the coefficient of friction.

    Surface deformation allows for more contact (ie over bumps and uneveness). The actual coefficient of friction is not affected. Wider tires provide more resistance to slippery spots or grit on the road. Race tracks have gravel, dust, rubber beads and oil on them in spots that limit traction. By covering a larger width, the tires can handle small problems like that better.

    Also... your wikipedia excerpt is uncited.

    The reason for wider tires is not that the increased contact area automatically leads to more friction (though there may be some effects that depend on the area indirectly). The design parameter that determines the coefficient of friction between the tires and the track is the something related to the molecular compressibility of the rubber. In other words, "the softer the rubber, the better the friction." However, when you use a softer rubber, you need to make the tires wide enough to give them strength. So, "the softer the tire, the wider it needs to be", to withstand design forces and moments.

    Also, narrower tires will tend to abrade rather than get tacky. Sticky tires have a weak sheer strength. This is compensated for by using wider tires. The larger area is needed to support large tangential forces.
    Last edited by XSL_WiLL; 08-31-2009 at 01:23 PM.

  16. #16
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    Quote Originally Posted by XSL_WiLL
    Surface deformation allows for more contact (ie over bumps and uneveness). The actual coefficient of friction is not affected. Wider tires provide more resistance to slippery spots or grit on the road. Race tracks have gravel, dust, rubber beads and oil on them in spots that limit traction. By covering a larger width, the tires can handle small problems like that better.
    Friction is resultant on surface irregularities - at least abrasive friction is. It is caused by these irregularities grabbing on each other. The area of the brake pad (and a tire's footprint) is the apparent area only. What Amontons law basically states is that the real contact area is independent of the apparent area for non-deformable objects.

    You're basically explaining how increasing the apparent area of a deformable surface increases actual contact area which in turn affects the coefficient of friction. Is that not changing the coefficient of friction? hint: Force of friction = coefficient X normal force and you're not changing normal force significantly with larger tires.

    Here's a citation:
    http://books.google.com/books?id=HWL...age&q=&f=false

    If you're wondering why I brought this in, it's because we don't live in a perfect world. There is no such thing as a perfectly non-deformable surface, there's no such thing as a perfectly deformable surface, there is no such thing as a perfectly elastic collision, no such thing as a perfectly non-elastic collision, and so on.

  17. #17
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    No. I said that it is NOT affecting the coefficient of friction. A given material has a given coefficient.

    Either way... larger tires is a poor example.

  18. #18
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    From what I've observed...

    Larger pads with all else being equal:
    Do not affect one stop power
    Wear out slower
    Heat up slower and dissipate heat quicker
    Are sometimes more likely to squeal

    These are my observations mostly on cars but also with bikes. I'm no engineer.

    I think one of the biggest misconceptions is a larger pad will increase one stop power.

    My pads seem to have no problem transferring heat into the BB7 calipers. Maybe the heavier calipers could be a good thing in that way.

  19. #19
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    At equal pressure, bigger surface gives greater stopping power IMO... Why give all the manufacturer bigger pads with the stronger brakes? I just imagined, I replace my pad with a nail. Theoretically (acc. to your opinion) no change between a bigger surfaced pad and a pointed nail (minimum surface area)?? It is nonsense, I think...
    If the surface is less, you need more pressing power to reach the same affect to the disc. Just try to hold something with one finger, or more...

    Im not an engineer either...

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