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  • Brake Caliper Piston Sizing

    Greeting and Happy Holidays!

    I will be building a custom brake set-up soon and I still have a few questions. I know that there are lots of different opinions and specific applications options in this area, but I am looking to gain some knowledge into known working set-ups and what seems to work best on the E30 M3. I am interested in 4 pot set-ups, but all can respond.

    What Piston sizes for F/R?

    Calculations for checking balance F/R?

    Thanks.

    Matt

    I DID SEARCH. Unless I missed something there is nothing really covering this SPECIFIC topic. (Now that I said this, I am sure someone will find it!)
    Last edited by Matts M3; 12-28-2007, 06:00 AM.
    -Matt

    For Aftermarket Engine Management, Visit Electromotive Store:
    http://www.electromotivestore.com

    Own a shop and need a better website?
    PM me or Visit http://www.shop-websites.com

  • #2
    You may want to pose your questions to Lee resident braking guru I'm sure he could be of some help Check his posts...

    http://www.s14.net/forums/showthread.php?t=29376
    Rich!

    Comment


    • #3
      Matt,

      What I did (so this must be the ideal approach, pay attention) is to use the stock bias as a starting point. In stock form, the front and rear discs are the same diameter, so brake torque is entirely dependent on the caliper piston sizing....

      The stock front brakes have approximtely 4576.12 sq mm piston area, and the rears have 2267.8 sq mm piston area, so the rears have approximately 1/2 the piston areas and thus half the braking pressure of the fronts..... That is usefull to know.... Since you will be working with four pot calipers, keep in mind for comparison purposes that to calculate their piston areas, you only figure the area of two of the pistons on one side of the caliper. You will find most aftermarket 4 piston calipers will give you slightly more piston area than the stock E30M3 front pistons. That was one of the reasons I did not go with 6 piston front calipers, even though the bling value would have been substantial. All the ones I could find increased front piston area further still, which would throw my plan out of balance and result in too much pedal travel, since I planned to keep the 25mm master cylinder....

      There are several variables that are difficult to calculate, and one of the big ones is exactly what the stock proportioning valve does... I decided early on to remove it (actually I gutted it and left it in place) and replace it with an adjustable proportioning valve. Since my car was modified with lower suspension and other changes, I knew I was in over my head to try to calculate ideal brake bias mathematically. My goal was to use hardware that was close, then tune in the ideal balance for various conditions using the proportioning valve. Since the proportioning valve can only reduce pressure to the rear brakes, not increase it, you just have to make sure the rotors and calipers you install have at least slightly too much torque in the rear (rear lockup) when the proportioning valve is not in use. Then with it, you can reduce rear line pressure to get the balance you need for various conditions......

      Clearly, you are going to need MUCH less brake torque in the rear than in the front. You "could" use the same diameter discs front and rear just as the stock setup does, and if you had the same relative piston sizing front to rear on your aftermarket calipers, that setup could be made to work. The problem with that approach is that the front brakes will be doing vastly more work, and you will wind up with the front brakes on fire before the rears even heat up. Also, there is the weight issue of using such a large rotor in the rear.

      I settled on a 330mm X 28mm front rotor, based on what was used on DTM cars, prior BBKs for similar cars, and because it would fit comfortably under the wheels I am using. In the rear I used a 315mm X 25mm rotor. That is slightly larger than some will say is "ideal", but I wanted to retain the rear parking brake setup and that was the smallest rotor that would allow me to still use the stock parking brake drum. It was also large enough that I was certain that by approximating the stock front/rear piston bias, I would have "enough" rear brake torque. I then went with front and rear four piston calipers with approximately the same front/rear bias that came on the car stock.

      I also installed an adustable proportioning valve, and a Spa brake bias gauge. The gauge is a PITA to install, because you need to install pressure sensors in the front and rear brake circuits. However, I found it invaluable for setting the car up once all the hardware was installed. You can see exacly how different proportioning valve adjustments effect line pressure, and you get a good mental picture of what sort of bias you need for differing conditions.

      You need a safe location to test things. You will at times inevitably have too much rear brake until you get things completely dialed in, and that is SCARY.....

      Or you could just buy Lee's setup. I am sure he will weigh in any second and tell you why his are the best in the world........

      HTH
      Last edited by Ironhead; 12-28-2007, 06:57 AM.

      Comment


      • #4
        Lee is probably still typing haha... (no offense Lee, I think you are very knowledgeable and I would love your opinion)

        So what size pistons are you using Ironhead?

        Also I would like opinions on these caliper brands (all assuming RACING calipers): Alcon, AP, or Wilwood

        Pad availability seems a little scarce on ALCON calipers, but there calipers seem to be of awesome quality and performance.

        Please try to set aside your bias

        Matt
        Last edited by Matts M3; 12-28-2007, 07:09 AM.
        -Matt

        For Aftermarket Engine Management, Visit Electromotive Store:
        http://www.electromotivestore.com

        Own a shop and need a better website?
        PM me or Visit http://www.shop-websites.com

        Comment


        • #5
          Originally posted by Matts M3 View Post
          Lee is probably still typing haha... (no offense Lee, I think you are very knowledgeable and I would love your opinion)

          So what size pistons are you using Ironhead?

          Also I would like opinions on these caliper brands (all assuming RACING calipers): Alcon, AP, or Wilwood

          Pad availability seems a little scarce on ALCON calipers, but there calipers seem to be of awesome quality and performance.

          Please try to set aside your bias

          Matt
          Hello Matt,

          I have a customer that switched from Willwood to AP Racing at the end of last season and said that the difference was night and day. He was actually able to shave quite a bit of of his lap times. The other big difference is the price. Ap are $$$

          Comment


          • #6
            My fronts have 4956.96 sq mm, rears have 2289.06.

            I honestly don't have any real bias toward one brand or another. AP will probably be the most expensive, but other than strange initial problems with discs cracking (which AP replaced for free) I have been very happy with their hardware. Also, you can email them and get detailed specs and drawings of basically everything they make. That was huge for me, because I could get hats and brackets machined before I even had all the parts in hand.

            The only reason I did not go with Brembo was I could not find the same selection of components of different sizes that I could with AP. I am sure Brembo makes a similar selection, but their marketing seemed to be geared toward selling complete kits, and I could not find specs/drawings of their components.

            My perception of Alcon was the same as yours...limited selection and availability.

            Not sure what to say about Wilwood. For years they had a poor reputation, but I am not sure how justified it was. And a lot of the slams you hear about Wilwood come from people who dropped big coin on AP or Brembo stuff. One thing is certain, if you go with Wilwood you can save big bucks. Beyond that, I will let Lee do the cheerleading for them.....:cheer2: :cheer2: :cheer2:

            Comment


            • #7
              Hi Keith. That same person told me that there was no major improvement after the swap. He is soon going to sell his used Wilwood set-up on this forum at a very good price. I think it'll be worth considering it. It uses front and rear forged Superlite calipers and two-piece rotors. AP Racing are good products. But not necessarely better than others that cost way less. Usually, they are also costlier to maintain. Price of rebuild kits can be 5 to 8 times higher. Cost of rotors and pads can also be significantly higher.

              I am not partial to Wilwood BTW. And see no problem working with other components too as long as they work properly and offer the proper data (AP and Wilwood are great at that - Brembo offers no specs). Many people have been judging Wilwood products by hear say or bad experience with their lower end products. But, strangely, for almost the same price it is possible to get great stiff products: Superlite forged calipers, SL6R radial calipers, and the new W6A-W4A. I also like the AP CP5200 when used with a 32mm rotor. Not a big fan of the narrower AP 28mm rotors for all-out racing (I have several cracked and warped ones on my shelves). I do sometimes have some problems with Wilwood though. The latest one involves a pair of SL6R calipers that Wilwood claims was machined within tolerance. The two receptacles for the mount's pods are too small. Wilwood claims they are at the lower end of the tolerated specs. I say they are just beyond. The pods will need a little sanding to loose 0.25mm in diameter. First time in two years though. My production has been within 0.05mm tolerance since I started. To the point where ambient temperature will affect the fit.

              Matt. To calculate piston size, I think that Ironhead clearly said it. In short, you must take in consideration the leverage effect (disc size) and the hydraulic effect (piston sizes). There is no reason to change the MC after a brake swap. As an exemple, Chris here, runs front 13" x 1.25" rotors and four 1.62" pistons calipers with rear 12.2" x 1.25" rotors and four 1.12" pistons calipers. Stock pressure limiting valve. The ball park is quite good. He's going to install a rear prop valve to get the perfect set-up, depending on track layout, fuel in the tank, and suspension stiffness.
              Last edited by LeeVuong; 12-28-2007, 07:44 AM.


              [email protected]

              1969 2002 racecar
              1989 M3 racecar
              e39 Touring

              Comment


              • #8
                Originally posted by keith View Post
                Hello Matt,

                I have a customer that switched from Willwood to AP Racing at the end of last season and said that the difference was night and day. He was actually able to shave quite a bit of of his lap times. The other big difference is the price. Ap are $$$

                Originally posted by LeeVuong View Post
                Hi Keith. That same person told me that there was no major improvement after the swap. Except for his lighter wallet.


                Cool! Conflict!.....:battle:



                Let the games begin!:nice!: :nice!: :nice!:

                Comment


                • #9
                  Conflict? Not really.

                  I have been friend with Keith's client (which I won't reveal the name) for a long time (around 15 years) and have discussed development of many elements in an M3. Exchanging ideas or just having plain fun. He even asked me how much he should sell his used kit and we came up with the same numbers. I was only reporting what that person told me. I hope it is not perceived as a confrontation with Keith. I admire his talented work. Just reporting. Sure, I too would like to have a racecar fully equipped with AP clutch, masters, brakes and such because it is what the works team used to have. But hey, if I can have another brand do the same work for less $$$, then I'll spend the money wisely. Cheers :chug:

                  For those who are interested, I have a client selling his front AP racing kit with CP5200 calipers and 330x28mm rotors. Kits is complete and a bolt-on. Was supplied by KVR.


                  [email protected]

                  1969 2002 racecar
                  1989 M3 racecar
                  e39 Touring

                  Comment


                  • #10
                    Ok Lee, now my question is:

                    What Wilwood calipers do you RECOMMEND?

                    Which do you think I might not be so happy with?

                    Matt
                    -Matt

                    For Aftermarket Engine Management, Visit Electromotive Store:
                    http://www.electromotivestore.com

                    Own a shop and need a better website?
                    PM me or Visit http://www.shop-websites.com

                    Comment


                    • #11
                      Hi Matt

                      Currently, two companies use some of Wilwood components on kits for BMWs. UUC and Massive (me) come to my mind. There may be others. Here are a couple of calipers I would recommend if you intend to do you own kit(s).

                      SL6R - Radial mounted caliper available with outer narrow body for extra clearance, and stainless steel pistons. This is a front caliper. Check part #120-7761-RS and #120-7762-RS
                      Being radially mounted, they require ore complex adapters/mounts than a lug mounted caliper.
                      http://www.wilwood.com/Products/001-...SL6R/index.asp
                      It is stiff, versatile and cost $350-$400. It uses 21mm thick pads.



                      A very stiff and cheaper option is the Superlite forged caliper. It is a lug mounted 4 pot caliper that uses the same pads as the above caliper.
                      It costs $150-$180 and despite its very low price, you get a lot of caliper. It is available for front and rear application. You won't be deceived. Fits 11.75" to 13" rotors.
                      http://www.wilwood.com/Products/001-...-FSL/index.asp


                      The new W6A and W4A are much bigger and to be used with 13" to 14.5" rotors. It has pads with a bigger area. Being a new caliper, it doesn't have yet the support from the usual known pads suppliers. That would use that caliper on heavy and powerfull e36-e46 racecars with 255 front slicks.
                      http://www.wilwood.com/Products/001-...-w6a/index.asp


                      For rear application. 4R/ST has the same body as the SL6R, only with 4 pistons. It is currently more expensive than th front caliper, but I am discussing with Wilwood to have a custom batch made with 1.12" stainless steel pistons at a much better price. Fits up to 13" rotors. I am also discussing with Wilwood for them to make that caliper available with 1.62" pistons for front application (for BMWCCA CR Prepared class).


                      Another rear caliper is the above mentionned Superlite with 1.12" pistons.

                      All the above calipers have stainless pistons and NO rubber dust boots.

                      Many kits I have seen, use the family of Dynalite calipers. They are most likely the ones to have given Wilwood a bad reputation. They have smaller pads and are soft calipers. Meaning not as stiff. I do have a few customers with those on their e30 (non-M) kits that are satisfied, but I don't use them anymore, except for rear application on lighter cars such as the BMW 2002. But even then, my own 2002 racecar has rear Superlite.

                      S-O-F-T
                      Last edited by LeeVuong; 12-28-2007, 10:00 AM.


                      [email protected]

                      1969 2002 racecar
                      1989 M3 racecar
                      e39 Touring

                      Comment


                      • #12
                        Excellent!!! Thanks Lee.

                        I am still in debate between Alcon and Wilwood, as I can get Alcon's for not much more $$$$$ but there seems to be only 2 options for brake pads.

                        I appreciate all the help. I will post my process, and results.
                        -Matt

                        For Aftermarket Engine Management, Visit Electromotive Store:
                        http://www.electromotivestore.com

                        Own a shop and need a better website?
                        PM me or Visit http://www.shop-websites.com

                        Comment


                        • #13
                          Every single US manufacturer of pads has many references for SL6R/Superlite calipers. Hawks, Performance Friction, Carbotech, Ferrodo, Portefield. And because they may sell lot more pads for these calipers, they end up costing much less. Per exemple an HT10 set for SL6R costs $115-$125, while it is $170-$200 for a BMW OEM caliper.

                          Also, when you pick a caliper. Make sure that the pad height will fit the rotors you also intend to use. Most AP, Alcon and Brembo calipers use tall pads (about 50 to 55mm), while the SL6R caliper uses a longer but shallower pad (about 45mm). Then figure what is the cost of replacement rotors.
                          Last edited by LeeVuong; 12-28-2007, 10:28 AM.


                          [email protected]

                          1969 2002 racecar
                          1989 M3 racecar
                          e39 Touring

                          Comment


                          • #14
                            Originally posted by LeeVuong View Post
                            Conflict? Not really.

                            I have been friend with Keith's client (which I won't reveal the name) for a long time (around 15 years) and have discussed development of many elements in an M3. Exchanging ideas or just having plain fun. He even asked me how much he should sell his used kit and we came up with the same numbers. I was only reporting what that person told me. I hope it is not perceived as a confrontation with Keith. I admire his talented work. Just reporting. Sure, I too would like to have a racecar fully equipped with AP clutch, masters, brakes and such because it is what the works team used to have. But hey, if I can have another brand do the same work for less $$$, then I'll spend the money wisely. Cheers :chug:

                            For those who are interested, I have a client selling his front AP racing kit with CP5200 calipers and 330x28mm rotors. Kits is complete and a bolt-on. Was supplied by KVR.

                            Hello Lee,

                            No problem . Just sharing some info I got from a friend. Willwoods are definatly alot more affordable.

                            Comment


                            • #15
                              All I would add, is that if some of the Wilwood calipers are in the $400 range, that is pretty close to what most of the AP stuff costs.

                              I generally believe you get what you pay for, but there is also clearly a point of diminishing return beyond a certain $$ amount.

                              For example, I would question how Wilwood can make a $150 caliper that is of the same quality as a vastly more expensive item from another manufacturer. The fact that Wilwood also makes calipers that cost 2 -3X as much as the cheaper ones, tells you the cheap Wilwood calipers are definitely lacking something.... What, I cannot say.

                              I imagine though, like Lee says, the upper end Wilwood stuff is probably good quality.

                              Comment

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