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CTS-v Brake upgrade not so much of an upgrade?

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  • #31
    Originally posted by DaveP View Post
    I don't understand how you come up with the clamp force of caliper #3 being the same as caliper #1. Caliper#3 has TWO pistons. It produces TWICE the clamping force. Yet you still cite the force of the two calipers as being the same. Where is the force of the second piston going? Disneyland?

    I'm out. I'm not a brake engineer. I'm done arguing for 5 f-in days. There's no learning taking place. My 2nd Gen brakes work great and cost me less than $800 all-in, so there's no impetuous for me to solve this.. I'm out of ideas. Have a Merry Christmas.
    Funny thing about learning; it's always taking place. You just get to choose whether or not you want to participate.

    Why pressure from only one side?

    This can be a little confusing and some very smart people have gotten caught. But it really isn’t that hard to understand if we shift our thinking a bit. First, ignore whether or not the caliper is fixed or floating; it doesn’t matter, and in a minute you’ll see why.

    Imagine that you are holding a book between your two open hands. Now squeeze on the book. If your left hand is pushing with 25 pounds of force, then your right hand has to push back with that much force or the book will move across your chest. Each of your hands is a brake pad, and the book is the rotor. The force between the pad and the rotor is only 25 pounds, not 50. And it is the force between pad and rotor that determines the frictional force generated on the brake rotor.

    In this respect there is no difference between floating and fixed calipers. The other side just acts to keep the rotor centered in the caliper, one moves the whole caliper, the other moves the other pistons.

    But wait! There are still two pads, one on each side. If we replace one pad with a ball bearing surface the force on the rotor from the brake caliper would be reduce about half. So we have to count both pads, but using the force generated by one side of the pistons.


    • #32

      I continued to think about this for two weeks.
      Yesterday, I took my good friend who's a naval architect to lunch and drew two calipers. One single piston with 3" of area, and an opposing two piston caliper with 1.5" area each piston. I explained our 1" area Master cyl with 100# of input pressure, he got it right away. 100psi. He looked at the two diagrams and said the single was making 300# of clamp pressure, and the second one 150# of clamp pressure. I said, Ok, you and every brake site and the guy I'm discussing this with agree. I don't get it. He kept trying different analogies, and could tell that I just wasn't getting it. Very frustrating for me, because I'm not the dimmest bulb in the chandelier, and I just wasn't getting it.

      Today I've spent hours on working with Free Body Diagrams. I began to get it. I read more online brake calculators regarding opposing piston, fixed, and floating calipers, etc. I began to get it even a little more. Then I decided to come back to this thread, and I see the "hold a book between your two hands and apply force. Like a damn light bulb went on. I got it! Yeah! I can't wait to take the naval architect out to lunch and give him the same analogy. He spent a lot of time with me, and he will be pleased that I finally understand.

      So back to the OP's Ty that won't stop: The front caliper piston area is too small. The rear CTSv calipers are roughly half the area of the stockers you took off. You need different calipers.

      Yeah. I get it. Thanks for the patience.


      • #33
        Originally posted by DaveP View Post
        So back to the OP's Ty that won't stop: The front caliper piston area is too small. The rear CTSv calipers are roughly half the area of the stockers you took off. You need different calipers.
        Ok, so now I'm even more confused... haha. Here's the link to the FRONT calipers

        I don't know where RealFastV6 was able to find the piston sizing for the rear calipers, but perhaps he can find it for the fronts? If I'm just looking at the pics of these front calipers, the pistons don't appear to be THAT much bigger than the pistons of the rear caliper, if at all. Which has me scratching my head... If the rear calipers I have are roughly half the area of the stock calipers, and let's say the front brembo caliper pistons are even 5mm larger than the rears, wouldn't they still have less area than the stock calipers?... If I can quote The Shawshank Redemption "Am I being obtuse?". I still don't get it.

        If the brembo calipers have a smaller area than the stock syty caliper, and a master cylinder that's barely different from a syty... then how in the hell are the same calipers (when installed on a cts-v) throwing me through the windshield, but not performing worth a damn on my Ty? Is it because the CTS has 4-wheel discs? I'm not disputing anything either of you guys have said, I'm just trying to understand what I'm working with, cause if I go off of the math, there's no logical reason why anyone would ever want to replace the stock calipers for these, other than it looks nice behind some 18 inch wheels.


        • #34
          The fronts are MUCH larger than the rears. 40/44mm if I remember correctly, and remember that area is exponential so 2x the diameter is 4x the area.
          Last edited by RealFastV6; 01-11-2019, 08:34 PM.


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