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  • #46
    Another point that has not yet been made about the OEM's brakes, is that if the MC has OEM suspension, then the diving of the nose under heavy braking causes considerable weight transference to the front end and this seriously disturbs the natural 50/50 weight distribution and must also completely bugger up (technical term) the front/rear brake balance.

    However, if you have stiffer suspension on the MC, particularly at the front of the car, the diving under braking is considerably reduced, which to my subjective impression, seems to improve the braking capabilities of the car. Since the rear wheels have wider tyres than the front wheels, if the car can be prevented from diving, then the rear tyres are able to do more work in stopping the car, which will help the car to stop more effectively/quicker.

    So, upgrading the suspension will also give an improvement to stopping ability of the OEM brakes without doing actually doing anything to the brakes. So you effectively get two mods for the price of one.
    /// Exdos ///
    "Men who try the impossible and fail spectacularly are infinitely superior to those who reach for nothing and succeed" --Napoleon Bonapart

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    • #47
      I obtained my new OEM floating rotors yesterday, and they've gone straight into the deep freezer, where they will live at -23degs C for the next 10 days before I fit them to the car. I'm sure that this will confirm to everyone that I'm as a mad as a hatter ( I might even agree with you!) However, before you all roll on the floor with laughter, I've done some research on this before I decided to try this as an experiment. There are a few companies selling "Frozen Rotors"; these are "cryogenically treated" brake discs which have been super-cooled in nitrogen freezers at around -190degs C, and the resulting brake discs are supposed to last twice as long as normal discs and have better heat capacity, therefore are an improvement on OEM brake discs. Apparently, this technique has become common in sophisticated engineering to harden parts such as engine parts. The theory behind this is essentially a continuation of the "quenching" of metals after heat treatment, which is normally done by immersing hot metal into oil/water to "freeze" the crystal structure achieved at high temperatures.

      From my "Googling" on this subject, I've discovered that there's something called the "Martensite Start Temperature", which is relevant to this cryogenic treatment. Basically, steel has a crystalline structure, and it is normally in a pretty randomised state known as "Austensite" but the crystal structure can change to a more uniform "Martensite" state. The change from Austensite to Martensite is temperature dependent and the Martensite Start Temperature differs for different materials. Since "steel" is an alloy of Iron, and there are thousands of different steel alloys, I have absolutely no idea of the actual composition of the OEM brake discs, therefore, I have no way of knowing the Martensite Start Temperature of the OEM brake discs. However I have seen a "phase diagram" of Martensite Start Temperatures which suggests that the Martensite Start Temperature of some steels could occur just below 0degs C. The OEM brake discs have a great tendency to rust, therefore I suspect that there's a very high iron content with not too many other high temperature melting metals in the alloy mix, therefore I would guess that the Martensite Start Temperature of the OEM discs is likely to be nearer to 0degs C than -190degs C. Whether the Martensite Start Temperature is lower than the temperature inside of my (wife's) freezer, I have no idea, but I would guess that -23degs C is the lowest temperature that these two OEM brake discs have ever experienced since the metal in them was first cast, because if they've been quenched before, then that would've been in oil/water and would have been at well above 0degs C. Therefore, if there is any change to be had in crystalline structure by lowering the brake discs to -23degs C, then it should occur now for me.

      The thermal contraction that has occurred by placing my OEM discs in the freezer will make the discs the smallest physical size that they will have ever been, and hopefully this contraction will occur below the Martensite Start Temperature thus triggering the transition from Austensite to Martensite. During my "googling" I came across some anecdotal evidence that some racers in the USA put their brake rotors in their domestic freezers before use, and they claim that it makes their brakes better and longer lasting, and that's where I got the idea from. It may be just wishful thinking, but isn't costing me anything to try this idea.
      /// Exdos ///
      "Men who try the impossible and fail spectacularly are infinitely superior to those who reach for nothing and succeed" --Napoleon Bonapart

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      • #48
        I'm actually lost for words John, you obviously have far too much time on your hands to research all this information!

        What I can't quite work out (chemistry was never my strong point) is that surely the metal will return to it's original state when exposed to high temperatures again?
        Last edited by Chris; 10-07-2008, 10:34 AM.

        Current - BMW M6
        Previous - Estoril S50 '98

        KW V3's, ACS Splitters, H&R ARB's, Rogue Engineering rear top mounts,
        Carbon Induction kit, Supersprint Exhaust, BBS 19" CH alloys, Strong Strut

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        • #49
          Originally posted by exdos View Post
          Another point that has not yet been made about the OEM's brakes, is that if the MC has OEM suspension, then the diving of the nose under heavy braking causes considerable weight transference to the front end and this seriously disturbs the natural 50/50 weight distribution
          I dispute that it seriously disturbs the weight distribution. Weight distribution change due to soft springs is only a secondary effect. Braking substantially changes the effective weight distribution, but this happens even in the absence of suspension. I believe that you can get to the vicinity of 75/25 distribution in a typical car due to the fact that the centre of gravity of the car is not in the same plane as the braking forces: this would happen even if the car had no suspension.

          My back-of-the-envelope calculations suggest that the centre of gravity moves by at most 10cm due to suspension travel.

          I think that excessive suspension movement makes the car feel less stable under braking, but I'd be very surprised if it had any noticeable effect on a simple straight line stopping distance test.

          Paul

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          • #50
            Originally posted by Chris View Post
            I'm actually lost for words John, you obviously have far too much time on your hands to research all this information!
            I'm retired, you should try it!

            Anyway, what are you doing participating on this forum when you're supposed to be at work???????

            Originally posted by Chris View Post
            What I can't quite work out is (chemistry was never my strong point) is that surely the metal will return to it's original state when exposed to high temperatures again?
            On the face of it, that would appear to be the case, and that this phenomenon lies behind certain compounds that are being developed that display "memory".

            However, from what I've read, once the Martensite structure has occurred, then this crystalline structure is normally stable and there is no tendency for it to reverse back to Austensite until the metal is heated to very high temperatures (above that occurring in brake rotors in normal use).

            Here's just one link for you to get an idea of what all this is about. http://www.cdpautomachine.com/ecatalog/cryo.html
            /// Exdos ///
            "Men who try the impossible and fail spectacularly are infinitely superior to those who reach for nothing and succeed" --Napoleon Bonapart

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            • #51
              Originally posted by pdwarren View Post
              I dispute that it seriously disturbs the weight distribution.
              Are you arguing the semantics of my choice of the word "seriously" here, or that the weight shift is no greater in soft suspension than stiff/no suspension?

              Originally posted by pdwarren View Post
              Weight distribution change due to soft springs is only a secondary effect.
              Correct. But, surely this secondary effect has an additional direct effect on braking performance overall?

              Originally posted by pdwarren View Post
              I think that excessive suspension movement makes the car feel less stable under braking, but I'd be very surprised if it had any noticeable effect on a simple straight line stopping distance test.
              Paul
              Surely the fact that excessive suspension movement makes a car feel unstable under braking is because the car actually is unstable in such conditions? Surely you've experienced a car squirreling around when the front has dived under heavy breaking, thus making it hard to keep in a straightline?
              /// Exdos ///
              "Men who try the impossible and fail spectacularly are infinitely superior to those who reach for nothing and succeed" --Napoleon Bonapart

              Comment


              • #52
                Are you arguing the semantics of my choice of the word "seriously" here, or that the weight shift is no greater in soft suspension than stiff/no suspension?
                I agree that there will be more weight transfer with soft suspension, but it's relatively small.

                I disagree that this will have a noticeable impact on the stopping distance, as it's not actually obvious that any weight transfer is bad for braking performance, even if you have wider tyres at the back.

                The increased weight on the front tyres increases the available stopping force at the front of the car, proportionally. Static friction = coefficient of friction x normal force.

                The coefficient of friction is a property of the compound, not of the contact area or tyre width, so unless you've got stickier tyres on the rear, there's no benefit to having 100% weight on the front wheels, rather than, say, 60% on the front and 40% on the rear.

                Surely the fact that excessive suspension movement makes a car feel unstable under braking is because the car actually is unstable in such conditions? Surely you've experienced a car squirreling around when the front has dived under heavy breaking, thus making it hard to keep in a straightline?
                I've felt cars squirreling under braking, but I've never particularly associated it with soft suspension, let alone with the weight transfer due to pitching which is a very small component of the overall weight transfer under braking.

                I remember when I first drove my car after replacing the OEM suspension, and, having driven against cars on stock suspension on a track, I believe that the increase in driver confidence due to the cabin not pitching and rolling all over the place is far greater than the actual increase in performance.

                Paul

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                • #53
                  Originally posted by pdwarren View Post
                  The increased weight on the front tyres increases the available stopping force at the front of the car, proportionally. Static friction = coefficient of friction x normal force.
                  I agree, but since the car has a finite weight, then increasing the force on the front tyres, will proportionally reduce the force on the back tyres and thus reduce static friction on the rear tyres as per the formula. Provided the car can be kept absolutely straight, then I agree that this shouldn't matter. However, in my experience this isn't always possible under heavy braking, especially when the road is not perfectly dry/flat/smooth, and sudden weight shifting/rolling under braking makes a car unstable and difficult to control.


                  Originally posted by pdwarren View Post
                  I've felt cars squirreling under braking, but I've never particularly associated it with soft suspension, let alone with the weight transfer due to pitching which is a very small component of the overall weight transfer under braking.
                  Try hard braking with suspension like that of a Citroen 2CV and it would be interesting to know if you still think the same afterwards.


                  Originally posted by pdwarren View Post
                  I remember when I first drove my car after replacing the OEM suspension, and, having driven against cars on stock suspension on a track, I believe that the increase in driver confidence due to the cabin not pitching and rolling all over the place is far greater than the actual increase in performance.
                  I would agree that uprated suspension gives more driver confidence over OEM suspension, which is an intangible property of uprated suspension. However, uprated suspension also imparts greater performance capabilities to the MC over that which OEM suspension can achieve and that is tangible, whether we have the talent to exploit those increased capabilities or not.
                  /// Exdos ///
                  "Men who try the impossible and fail spectacularly are infinitely superior to those who reach for nothing and succeed" --Napoleon Bonapart

                  Comment


                  • #54
                    weight transfer to the front may actually increase braking performance as there is more grip at the front and therefore as most of the braking is done at the front its better. The larger size rear tyres won't have as much grip as the fronts underbraking as the weight is pushed forward. Stability is another matter.
                    Ex 2001 S54
                    New cars:
                    Lotus Carlton
                    350Z

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