Designing Brake Calipers

srcoates
srcoates Posts: 15
edited July 2010 in Workshop
Hello everyone,

As you can probably see this is my first post on here, but I have been reading regularly as a guest...

I wanted to tap into your opinions if I may... I have recently started riding a road bike and love every minute of it (apart from the occasional hill which appears to be irrationally steep!), however one thing I have noticed about my bike is that the brakes are relatively poor.

My bike has FSA Gossamer calipers (which I am aware aren't exactly going to be 'top of the range') andI rode a friend's bike with Ultegra brakes - the difference was huge (in terms of bite, feel and power). The main difference I could see between the components were that a) his were Ultegra and mine were Gossamer and b) his brake blocks were of the cartridge type, where as mine are the old fashioned block type (both Ultegra material).

I am a design engineer by trade and have decided to embark on designing my own calipers to replace mine rather than just buying new ones... I know I can get the weight out without any trouble, but where your help comes in is knowing what makes a 'good' brake caliper different from a 'fantastic' one? I currently assume that the lightest stiffest caliper is the holy grail. Is that correct? Also is it fair to assume that the cartridge type pads are the way forward due to their stiffness?

Feedback/advice gladly received! Cheers!

p.s. I know it would be easier and cheaper to go and get a pair of calipers from a bike shop, but that would be too easy!

Comments

  • PhilofCas
    PhilofCas Posts: 1,153
    can't add much, other than to say i have the "old fashioned block type" pads (bought the cheapest i could find) and my brakes are pretty decent (ageing Campag Xenon's), so design of the brake itself seems to be key
  • cooldad
    cooldad Posts: 32,599
    Cartridge pads are designed to be quicker to replace, they won't necessarily work better or worse.
    The caliper really makes the difference..
    I don't do smileys.

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  • cooldad
    cooldad Posts: 32,599
    ps see

    http://www.paulcomp.com/

    for machined bits
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

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  • Monty Dog
    Monty Dog Posts: 20,614
    Look at Zero Gravity, EE Brakes for inspiration - there are some very lightweight brakes about. Cartridge pads do make a difference - you can use a softer compound pad for more bite but the stiffer holder means that it doesn't flex and defeat the object. A caliper designed for machined parts needs to be different for forged parts to account for the metallurgy of the components.
    Make mine an Italian, with Campagnolo on the side..
  • srcoates
    srcoates Posts: 15
    Cheers guys.

    Monty, good point about the cartridge pads and brake compounds... That makes a lot of sense.

    I had seen the Zero Gravity brakes before but not the EE Brakes. I have to say they are very nice!

    Anyone got any experience with whether stiff is best (so to speak!)? I notice that Shimano make the rear calipers 'less stiff' to give an effective brake biasing...
  • dennisn
    dennisn Posts: 10,601
    Just to play devils advocate a bit here. Remember that you will be counting on these things to STOP your forward progress before that intersection or stop sign or train or whatever. I don't recall ever hearing about a modern brake set failing, so the basic design must be fairly good and they all resemble each other which probably says a lot for the general design itself. Good luck. Sounds like a nice project. Keep us updated. Who knows, we may ALL soon be buying your brakes.
  • srcoates
    srcoates Posts: 15
    Dennisn, I agree... It is rare that a design is widely adopted unless it is good (all-be-it not unheard of!) so I was thinking of sticking with a dual pivot design, at least to begin with.

    I think the first attempt will be a learning excercise regardless of the success of the outcome. My main objective will be to (safely!) exceed the performance of my existing calipers for a reasonable weight reduction (aiming for 1/4 to 1/3 off).
  • nicklouse
    nicklouse Posts: 50,675
    srcoates wrote:
    I notice that Shimano make the rear calipers 'less stiff' to give an effective brake biasing...

    are you sure as the arms are interchangeable. the only difference is the length of the mounting bolt and nut.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
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  • srcoates
    srcoates Posts: 15
    nicklouse wrote:
    srcoates wrote:
    I notice that Shimano make the rear calipers 'less stiff' to give an effective brake biasing...

    are you sure as the arms are interchangeable. the only difference is the length of the mounting bolt and nut.

    Just looked into it, yes you are right... That was me reading too much into a photo that didn't show them very well!!!
  • bigmat
    bigmat Posts: 5,134
    Some Campag brakes have a single pivot at the rear, to provide braking differential / reduce weight where its not needed. There are some lightweight single pivot (front and rear) brakes on the market as well.
  • mrushton
    mrushton Posts: 5,182
    have a look at the bontrager calipers and their xxx version. Slightly different but still v.good
    M.Rushton
  • synchronicity
    synchronicity Posts: 1,415
    Personally I think there is enough competion already in the brake caliper market. Now FSA & SRAM have joined in as well.

    also have a look at the TRP970SL brakes as well as M5 and Ax-Lightness for further inspiration. I think the ZG gravitas are supposed to be right up there with the best.

    Oh and I think the oveall leverage ratio between brake levers & calipers is the key to power. Then if you make things too light & your brakes flex, either in the calipers, or in the brake lines themselves, it reduces effectiveness and you end up with a mushy brake.
  • Wheelspinner
    Wheelspinner Posts: 6,608
    Want another variable? Remember the cable outer has quite an impact on feel and power too. Get some really good "compressionless" cable outer housings, will help as well.
    Open One+ BMC TE29 Seven 622SL On One Scandal Cervelo RS
  • srcoates
    srcoates Posts: 15
    Thanks for your input guys.

    synchronicity I agree there are lots of brakes out there already, but I don't intend on retailing mine. I will do a run of two for my bike only, and if people I know would like a set too then I will get them made as well. Even in short runs I will be able to get the brakes for a fraction of the cost of the big brands, but with the added satisfaction of having done them myself!

    So in summary the brakes need to be as stiff as possible, with as little mass as possible! Just as I thought, but I wanted to check that there were no curve balls that I wasn't aware of!

    Cheers!
  • Wheelspinner's correct about the brake cables - both inner and outers. I was appalled recently by the spongy performance of new Dura-Ace calipers I fitted - and then I changed the brake cables. What a difference!

    Making your own calipers would be a most interesting project - provided you've access to some decent 3D CNC milling equipment. Or you're pretty handy with hacksaws and files!

    I suspect the biggest headache will be sourcing the return springs, as they're usually pretty special to the design. Perhaps you could consider using an existing spring off an el cheapo brake set and starting your design from there.

    If you're talking short runs and getting them sub-contract machined, I doubt very much that the selling price of yours will have folk rushing at you with open wallets....best of luck, anyway, and keep us informed.
  • dennisn
    dennisn Posts: 10,601
    You might want to have a look at the old Campy C-Record brakes for ideas and inspiration. They were "different".
  • srcoates
    srcoates Posts: 15
    Thanks Nigel, I will keep the cables in mind... Certainly a valid point that I have to admit I hadn't considered before (the cable outer that is, I had just thought about the inner stretch...)

    For information, I will design them on CAD and get them run through FEA to optimise the stiffness. I will use my FSA ones (which I have the material specs & a representative CAD model of) as a baseline and improve from there. I will also model my friend's Ultegra calipers and see how they perform in FEA world. From that point I will get them CNC machined by a local firm. Depending on the final design I may shot peen them, then finally anodise them. You are right, the price for such a low volume wouldn't be too competitive
    but I still expect them to be cheaper than a set of EE brakes or Zero Gravity ones... (Don't get me wrong, I am not presuming that they will be as good as them either!)

    For the first iteration (that is presuming I am still interested after the first set!) I will use all the existing components off of the FSA ones that I currently own (springs, quick releases etc.)
  • dennisn
    dennisn Posts: 10,601
    FWIW brake calipers that are CNC'd may not be as strong as forged ones. Which is how
    the Big 3 component makers do it. I THINK.
  • srcoates
    srcoates Posts: 15
    Dennisn, you are right, forged will be stronger, but not night and day...

    The big manufactures will forge them because the manufacturing costs are lower for high production runs with forging (initial tooling costs are high, but that is then spread over thousands of components). You also get very little material wastage unlike machining.

    It is true that the grain structure is better in forged parts, but there is also an argument that cold forging aluminium will also have adverse effects on the material.

    Ultimately though strength isn't an issue with the calipers, it is entirely stiffness driven, and you will probably end up with huge factors of safety for the component stress in order to achieve the required stiffness. So in this situation it isn't really an issue.

    A lot of manufacturers use the 'forged to retain grain structure' line to grab peoples attention and to boost the appeal of the product. Whilst it is undoubtedly true to a degree, if a component is designed correctly you will get a better component out of CNC than forging due to the restrictions imposed by the forging process...
  • lae
    lae Posts: 555
    That's a really interesting project!

    I guess the fact that you can very easily loose traction on both wheels* means that caliper power is good enough. I suppose that gives three areas to work on

    1. Stiffness - for better feel through the brake and finer control
    2. Weight
    3. Aerodynamics

    I don't really know why calipers all use a one-bolt mount to the forks - rules and inertia probably. This seems to be a good area to increase stiffness, but would almost certainly mean building your own forks too (got an autoclave?). Perhaps a two-bolt mount at the fork crown, or a mounting system that's integrated into the fork blades itself (which could be built as an aerodynamic housing for all the pivots and stuff - and possibly by removing the arms could save weight too). The pivots, which are probably the main source of flex in a caliper, could be much more rigidly mounted in this way.

    Also it seems that the pad carriers themselves only have a single mounting point which could be quite flexible. If you could make your own carriers too, you could use two bolts rather than one, or a slide-on carrier that has a bolt at one end. Slide-on carrier would make adjusting the pad toe angle difficult though... A double-bolt pad carrier would increase the depth of the arms which would increase their torsional rigidity too.

    Weight could be saved by re-designing around a double cable system - BMXs use a y-shaped cable that could possibly be used to pull on both halves of the caliper separately, meaning that there's no need for the very substantial arms that cross over the top of the wheel.

    * is a lightweight ABS system needed? Motorbikes have it...
  • chriskempton
    chriskempton Posts: 1,245
    Take a look at Planet X's own brand brake calipers as well - they offer forged and CNCed in (to my eye) a virtually identical outward design.

    They offer a very good price and weight with reasonable performance as well so worth a look.
  • satanas
    satanas Posts: 1,303
    Some dubious assumptions being made here IMHO.

    First, stiffer isn't always better. Yes, it's good if the parts of the arms between the pads and the pivots don't flex too much - otherwise the brakes might squeal - but it's not always a bad thing if the upper bits flex a bit as this can give better feel; this comes down to personal preference.

    Second, more powerful isn't always a good thing. What is most important is for the brakes to be powerful enough, and to have the best modulation possible. It can be annoying/dangerous if the brakes grab at high speed - as my DA 7800s sometimes tend to do. I also have the DA 7400 brakes and IMO these have a better balance between power and feel, whereas DA 7700s were widely criticised for lacking power, which I would agree with. So, it's not so simple even for Shimano to get things right in my experience, and I'd be very reluctant to buy the supposedly 25% more powerful DA 7900 brakes if they're grabbier than the 7800s.

    Re Campag Delta brakes: somebody always says these are the greatest things since sliced bread <sigh>. I worked in the industry when these were around and have ridden them (unfortunately). Yes, they look different - and IMO worse - but they were heavier than the sidepulls of the time, less powerful, had poorer clearance, were harder to work on, and more likely to fail mechanically, or have parts go AWOL. They also required a totally non-standard 3.5mm Allen key for the cable clamp bolt. They were terrible things IMO, and I worked for the importer at the time, so had wanted to like them. This proved impossible.

    Bottom line is that I would much rather have a reliable brake with good feel and good clearance than something "cool looking" with poor spares availability, and more chance of failure. IME, cold-forged brakes from the larger companies do what is needed, and are both easy to get spares for and unlikely to need any. This is good. The reason why smaller companies use CNC machining rather than cold forging is due to economics, and *not* because the result is a superior product, claims to the contrary notwithstanding. They may be better conversation pieces/pose value but is that really a sensible reason to shell out lots of cash for something that is often functionally inferior?
  • srcoates
    srcoates Posts: 15
    Thanks Satanas... Interesting post.

    I can see what you mean with regards to stiff calipers being harder to modulate (and more 'grabby').

    I agree with your synopsis on the manufacturing techniques as well. Too much is read into manufacturer's claims for using a specific method (regardless of whether they are a large or small company), as ultimately it will come down to manufacturing a cost effective product.
  • satanas
    satanas Posts: 1,303
    Another point: Back when the Commonwealth Bank Classic was held here in Oz I worked for the sponsor of one of the teams and serviced their bikes. Although these guys were theoretically amateurs, many became pros soon afterwards. All these guys (over a number of years) insisted that their brakes were adjusted as far from the rims as possible while still (just) working. The idea was that then the brakes wouldn't rub under load, could tolerate a bit of misalignment from wheel changes, etc, and that the wheels could go out of true a bit without causing a drama. If anyone dared tighten the brakes we heard about it immediately!

    On the other hand, many "weekend warrior" types seem to believe that good brake adjustment = as close to the rim as possible. Bad idea! Apart from the problems listed above, it is often quite difficult to apply the brake if it's adjusted too tightly - unless one has very large or powerful hands. This can be particularly the case if one mostly brakes from the hoods, rather than the drops. In fact, I usually adjust my brakes so that my hand is at a comfortable stretch when the pads hit the rim; this is generally the most comfortable if long descents with lots of hairpins are likely. The result is between the other two cases, i.e., neither super tight or super loose.

    So, I think there are a number of important things for brake callipers:
    1. Powerful enough
    2. Good modulation
    3. As much clearance as possible under the calliper
    4. Reliable
    5. Stiff where needed
    6. Light weight - but not so light that it compromises any of the above points
  • srcoates
    srcoates Posts: 15
    Fantastic, thanks satanas,

    Exactly the kind of feedback I was looking for.

    Cheers!
  • rake
    rake Posts: 3,204
    im wonder srcoates, are you able to machine a bearing shim from aluminium to make a sram htII bb convertor.
    a tube off 11.5mm length with 22mm internal diameter, 25mm external diameter for 7mm with a 29mm diameter shoulder for the other 4.5mm. cheers. could be interested in a quantity of them. its to press fit into a standard sized 6805 deep groove rubber sealed bearing and close slide fit over a 22mm shaft.
  • srcoates
    srcoates Posts: 15
    Hello Rake,

    I am afraid not. I will be getting someone else to machine the parts I design. Try a local machine shop. I think you will be suprised how little they will charge you...