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  • #16
    Originally posted by paulm3 View Post
    for that price.. you might as well get a set of stop techs or ap bbk's???
    And, they'll be lighter too. The MC's OEM brake calipers weigh 3.26kgs each and those 135 6 pots weigh 5.19kgs each, so you'd be adding weight in the wrong place to the unsprung weight.
    /// 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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    • #17
      Over 5kg's for the BMW upgrade calipers is crazy! The Porsche Brembo calipers I fitted were
      over 1kg lighter the oem one's, which I thought were very heavy!
      Black S50

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      • #18
        interesting post from another forum regarding the BMW performance bbk set up :-

        qoute,

        I made the post below in relation to a question a UK member posted, asking about the value of changing to the BMW BBK system and also why it was so cheap in comparison to the 'proper' BBKs like APs or Brembos. His car was a 325i, he liked to do a little track work, but mainly his car was used on motorways/highways for his work commute. Thus my response is European focussed, with UK pricing - however the principles of the post remains the same and I think it might be valuable here too.



        Quote:
        Originally Posted by E92Fan
        The BMW BBK system is undeniably good value - 6pot Brembo calipers at the front, 4pot rears, drilled discs, different pads. For the money, it's unbeatable

        However, you have asked a very valid question as to why they are so cheap. The thing with 6pot brakes is that across the range there is a HUGE variation in quality and performance.



        Firstly, it would be an idea to understand a little bit about the design of multiple-pot calipers and the advantages/disadvantages of certain systems.

        Generally, and in the most simplistic view, the most important aspects of a brake caliper design are -

        a) the technical suitability of the caliper force in relation to the target vehicle
        b) how evenly it distributes braking force across the entire face of the pad,
        c) the heat resistant capability of that caliper in terms of the way it can dissipate heat away from the pads,
        d) the long-term durability and reliability of the caliper
        e) weight


        There is a common misconception that the greater number of pots the better the braking system. A bigger set, or a greater number, of caliper pistons will provide more clamping pressure on that axle, but could also have a negative effect on total brake performance. If the pistons are too large for the application it will lead to excessive pedal travel and the front/rear brake balance will be adversely affected, resulting in longer stopping distances. Clamping forces can also become so strong that you'll end up locking the brakes far too early, making brake modulation and control very difficult.

        In reality, the number of pots is not as important as the technical design and setup of each caliper to a particular vehicle. In the most simplistic terms, the greater the number of pistons/pots, the greater the surface area of pressure being applied to a brake pad, and hence the greater amount of friction generated (assuming the brake pad characteristics haven't changed in the comparison). However, it is more important that the correct braking force is distributed along the pad - having a more efficient 4pot system valved correctly for the vehicle will give much better braking performance than an oversized 6pot caliper with mismatched valving.

        A larger brake caliper normally leads to using larger-sized pads - however, just because a pad is larger doesn't mean that there is more braking force. A bigger pad of the same compound in the same location as a smaller pad will not actually give shorter stopping distances. The stopping force or torque reaction is derived from the pad friction coefficient, the diameter of the brake disc and the amount of pressure applied. A bigger pad does not apply more pressure, only the same pressure over a bigger area. The advantage of a bigger pad lies in its heat capacity and rate of wear - the larger the pad, the more it will be able to absorb initial heat, thus suffering less thermal shock and with the consequent advantage of greater pad life.

        However, there are sometimes problems with having larger pads - the popular Porsche calipers use a taller pad than most other systems, and whilst this taller pad gives slightly better heat characteristics, the system actually requires a heavier brake disc to match. This heavier disc has greater inertia and if the piston valving pressure is not adapted to suit, you actually end up with longer braking distances.

        Piston/caliper design is also important - the cheaper calipers generally use stainless steel or aluminium alloy pistons coupled with simple dust boots, and are almost always of a two-piece cast aluminium design. The most expensive calipers may use titanium pistons (lighter and stronger), with much better high-temperature dust seals on each piston. They may also be of a forged monobloc design, which if designed using the correct alloys may well be stronger than a regular caliper, but may not necessarily be stiffer. A big brake kit will provide increased heat capacity, which means substantially more resistance to brake fade and caliper distortion with multiple stops from high speed. The stronger the caliper, the less the distortion and the more precise the braking performance. It will also give a firmer pedal due to stronger and stiffer components, as well as better modulation characteristics. The lighter the caliper the greater the reduction in unsprung weight, which will yield better handling and suspension characteristics on a properly setup car

        Some calipers also use a differential bore design, in which smaller pistons are used up front, with larger pistons at the trailing edge of the caliper. As the surface of the brake disc heats up, the clamping force of the pistons has to be increased to maintain braking force (due to increasing fade). If the caliper has multiple pistons (or multiple pairs of pistons), the brake disc surface is initially heated by the pistons pushing against the brake pad at the leading edge of the caliper, making the disc surface hotter when it rotates back to the pistons closer to the trailing edge of the caliper. Therefore it helps if the pistons closer to the rear edge of the caliper are larger as they can deliver greater pressure.



        So, with all that in mind then, why's the BMW BBK such good value?

        Pros
        Well, it's a basic 6 pot system (front), designed by Brembo as a two-piece aluminium caliper. It uses inexpensive standard compound Jurid/Textar brake pads (which are the regular BMW OEM pads), with basic one-piece drilled & slotted 338x26mm discs, simple individual piston dust seals and standard BMW brake hoses.

        Because the caliper, and entire brake system, was designed as an OEM piece for the 135i, BMW have managed to drive the cost of that caliper down and hence can pass on the savings to the aftermarket customer. The only difference is the brake disc, which on the Performance kit is the same intrinsic disc but now drilled and slotted. The ancillaries have also been built down to a price - this is not being disrespectful to BMW, but in reality you can't imagine BMW using a £1500 brake system as standard on the 135i. For regular road use and as a standard no-thinking-required replacement for standard brakes it's a very good kit. The vast majority of BMW drivers would be very happy with this BBK as it's a fit-and-forget system And compared to the brakes on a 325i (not so much to a 335i/d) it's a vast improvement.


        Cons
        However, when you start exploring the higher limits of the BMW BBK there are several failings that become obvious. Firstly, it is next to impossible to get aftermarket pads for that caliper - because it's a BMW-specific caliper and not a standard Brembo shape, the likes of Pagid and Ferrodo have been very slow in developing aftermarket pads for that application. The regular BMW pads are ok for road use, but on the track they start to fade and judder very quickly. The more aggressive driver or track-day enthusiast will probably find the limits of the pad quite quickly. To be able to change to Pagid race pads for use on a track for example might be very important and necessary. Continuing this theme, it isn't easy to change the pads on the BMW BBK - the caliper has to come off. Compare that to the top-end Brembo kits where the pads are held in by quick-release pins and you can do a pad change in mere minutes.

        The brake discs are one-piece items with integral bell (the bit that holds the disc onto the hub). There's no way to improve the brake disc by using aftermarket items from the likes of Performance Friction (who make arguably the world's best brake discs). The standard discs themselves also aren't as heat-resistant as they could be and will warp more easily under duress. The heat characteristics of the pistons also leave much to be desired - when out on track, under duress the pistons have a tendency to crack, whilst the seals will almost certainly disintegrate. This has been shown many times now on the 135i race cars. The caliper also displays quite uneven pressure distribution across the pistons - the last set of pads I used on my BMW BBK were noticeably warped with a 3.5mm height difference between the widest edges.

        These problems only showed up when the brakes were put to more serious use. I discovered all this first hand at the Nurburgring last summer, when I subjected the brake system to only a moderately torturous test I was actually disappointed at how spectacularly the calipers failed I was reminded though that they are also spectacularly cheap and not really designed for that sort of abuse!! To BMWs credit they replaced that first kit with a new set of calipers..!

        On normal road driving, the limits would not be anywhere close to being reached and so I would still recommend them as a significant performance upgrade to the standard brakes on anything up to a 330 (pre-LCI) under these conditions

        I would NOT recommend the BMW BBK for someone with a 335i or 335d, as there are too many disadvantages going to the BBK compared with the regular OEM setup - the main problem is the discs are much smaller and thinner and can't absorb anywhere near the amount of heat that the OEM discs can.

        A 335i/d owner would be better off keeping the OEM calipers and discs and instead change the pads to something more suitable for fast road, uprate the brake fluid to at least a DOT 4.1 level, and upgrade the OEM rubber brake hoses to stainless steel items.



        My thoughts

        If you are looking to use the car on a track on more than the odd occasion, or do LOTS of high-speed driving, then I would suggest you look at a higher-spec alternative. There has been mention of the £4000/£6000 Brembo GT kits etc, which are fabulous but massively over-specced for use on anything other than fully-fledged race cars.

        The Tarox kits have issues of their own - the cheap kits are exactly that - cheap and nasty. The 12pot systems are ridiculously expensive, and to be honest why on earth would anyone need a 12pot system? The individual pots themselves are tiny, the weight of the caliper is huge, and the performance doesn't justify the price.

        Probably the best value kit, and the one I'm now using to great effect, is the AP Racing 6pot front / 4pot rear system. The front 6pot system is a two-piece cast aluminium design using 355x32mm slotted and vented discs with separate bells, aluminium alloy pistons with individual high-temp dust seals and comes supplied with mounting brackets, braided hoses, Ferrodo DS2500 fast-road pads, and Dot 5.1 brake fluid.

        The rear system uses a 4-piston version of the same caliper, Ferrodo DS2500 pads, but uses the standard rear BMW OEM discs. I believe that Stillen Racing in the USA have a different version of the rear AP system that uses replacement discs as well.

        I have been using the APs for almost a year now, and I have nothing negative to say about them at all. They've handled every track day I've thrown at them, the durability is excellent, pedal feel very firm yet progressive, and are a huge improvement over the BMW BBK which I had on previously. It's no wonder they are used on so many race cars at the Nurburgring as the performance/cost ratio is staggeringly good value. I will be doing a separate write up on the APs so keep an eye out for that.

        Retail cost for the complete front AP kit (CP5575-1009.G8) is £1,887 + VAT and fitting .
        The rear kit (CP6625-1000BK) is £815 + VAT and fitting.
        (from Birds - www.birdsauto.com)
        (Product codes are for Black-coloured calipers - Red calipers also available)


        Bottom line - for normal road use on anything up to a 330 (pre-LCI), get the BMW BBK. For serious use, get the APs. If you just want to spunk a load of money on the big Brembo GT brakes, buy yourself a better car first...!!!!


        __________________

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        • #19
          dave: Thats a really insightful read, thanks for posting! I had my discs/pads replaced this year all round, so I wont be doing any big upgrades in the near future. Nevertheless it is good to know what are the options and how good they are


          Regarding the weight - the article I saw it was specifying e36 m3 caliper (which are the same as ours) weight as 5.1kg, being just 0.1kg lighter than 6-pots. But according to ETK is the same as exdos wrote...

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          • #20
            couple of pictures of a Brembo set up on a m coupe,



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            • #21
              Originally posted by inside View Post
              dave: Thats a really insightful read, thanks for posting! I had my discs/pads replaced this year all round, so I wont be doing any big upgrades in the near future. Nevertheless it is good to know what are the options and how good they are


              Regarding the weight - the article I saw it was specifying e36 m3 caliper (which are the same as ours) weight as 5.1kg, being just 0.1kg lighter than 6-pots. But according to ETK is the same as exdos wrote...
              not my comments but very interesting views, I am still tempted by the BMW performance kit and may have them fitted to my coupe, someone local to me is looking into having brackets made at the moment and I will post more details as I get them.

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