In Reply to: Re: Disk brake design, Ari [Profile/Gallery] , Thu, 16 Jan 2003 13:40:22

In theory, the pressure in the system that is transmitted to the pads is constant regardless of pad size. That's why a small master cylinder can drive 4 larger caliper pistons at each wheel. Pressure x Area = Force.
So if you increase area and hold pressure constant, you will get more force. That's the magic of hydraulics. So JJ, you're right, bigger pads will apply more force(up to a limit).

Another example is a hydraulic jack. A small amount of force from your arm can produce high pressure in a small cylinder. This high pressure is transferred to a large cylinder capable of producing the force to lift a car. Conservation of energy(no free lunch) dictates that you have to make lots of arm pumps on the small piston to move the big one a small amount, but the force is multiplied...not divided as Ari stated.

Therefore, with constant pressure, a larger pad will transmit more force. In practice, the limit to this is pad flex. If pads were truly rigid, you could use a tiny piston and a much larger pad. When cars need more braking force and need a larger pad, sometimes dual pistons are used to overcome this flex. Stopping effectiveness is also greatest on the outer area of the rotor where leverage is greatest.

I think this is the first one Ari has ever missed...I admit to several goofed posts, but not this time.

posted by 216.75.9...

• Disk brake design, JJ, Wed, 15 Jan 2003 20:24:45
  • Re: Disk brake design, Ari , Thu, 16 Jan 2003 13:40:22
    • Re: Physics error on pressure concept, rest is correct, JohnK, Fri, 17 Jan 2003 16:28:33 <-- Viewing This Message
    • Wow!, JJ, Thu, 16 Jan 2003 14:57:26
      • Yup, Ari , Thu, 16 Jan 2003 15:15:40
  • Upgrade to 9000 brakes...., Chaz, Wed, 15 Jan 2003 21:33:34
    • Re: Upgrade to 9000 brakes...., gorper, Thu, 16 Jan 2003 01:08:04
    • Chaz, you can do that ? How does it affect cars with, Alex Bucell, Wed, 15 Jan 2003 21:43:38
      • Re: Chaz, you can do that ? How does it affect cars with, Justin VanAbrahams , Thu, 16 Jan 2003 11:48:10
      • In theory, should work...., Chac, Wed, 15 Jan 2003 21:52:19
        • Chac=Chaz...oops, Chaz, Wed, 15 Jan 2003 21:53:23
          • Re: my saab seems "over braked"..., trog100, Fri, 17 Jan 2003 09:34:05

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