ChasR
RR Helper
motivation
Posts: 10,194
Club RR Member Number: 170
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you need to calculate the piston area to compare braking effort e38 has 4 pistons, but the piston area is only the same as the 62mm [IIRC] single piston in the V8 e39 sliding calipers. Audi S4s have the same size pistons, but use a radial mount caliper that might be easier to fit. The 406 and fiat calipers have smaller piston area. Depending on size you may need a bigger master cyl. biggest 4 pots are on Lexus 430s This. When doing your calculations you have to double up the figures IIRC for sliding pot calipers ; the argument is that the opposing pistons are there to simply react against the opposing pistons. In my case there was a massive discrepancy.
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heathrobinson
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Broken everything
Posts: 848
Club RR Member Number: 111
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That I did not know! So, if I've got this right, my Granny callipers are 60mm, so 2827mm squared. Mondeo ones are 57mm, and 2551mm squared. The E38 four-pots have a total piston area equivalent to a 62mm dia piston, so 3019mm squared. However, as the single pots are sliding callipers, they're equivalent to a calliper with an area of 5654mm squared? Is that in braking force, or in working out what size of MC to use? Eg. If I change to the Beemer four-pots, would they be just over half as effective as what I have on there now? Why would anyone bother with all the added complexity when you'd need tice the sixe of calliper to achieve the same result? Or am I getting that wrong? It's late, I'm guessing I've misunderstood that fairly comprehensively! Were all things equal, the Beemer/Audi ones offer a little more force for a bit more travel than my current setup, which sounds about what I'd want. The mondeo ones sound like a step backwards except for the ease of fitting. Also, the Granny callipers that I'm referring to are the honking great single piston jobs off the Granada Scorpio Cosworth mk2cossie. I'm fairly sure that they're a bit bigger than the two-pots. I'd like to have a look at pad area too, as that's a difference between different designs of calliper. The ones I have at the moment have quite a deep pad. Anyone know how they compare to something like the beemer pads? Thanks again guys, I might be a bit befuddled at this hour, but I'm learning a good amount from all this!
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ChasR
RR Helper
motivation
Posts: 10,194
Club RR Member Number: 170
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That I did not know! So, if I've got this right, my Granny callipers are 60mm, so 2827mm squared. Mondeo ones are 57mm, and 2551mm squared. The E38 four-pots have a total piston area equivalent to a 62mm dia piston, so 3019mm squared. However, as the single pots are sliding callipers, they're equivalent to a calliper with an area of 5654mm squared? Is that in braking force, or in working out what size of MC to use? Eg. If I change to the Beemer four-pots, would they be just over half as effective as what I have on there now? Why would anyone bother with all the added complexity when you'd need tice the sixe of calliper to achieve the same result? Or am I getting that wrong? It's late, I'm guessing I've misunderstood that fairly comprehensively! Thanks again guys, I might be a bit befuddled at this hour, but I'm learning a good amount from all this! You are almost there . As said, sliding calipers effectively have a second piston for the matter of the Effective Piston Area (EPA). The EPA is what you are calculating. The EPA is critical for the master cylinder vs. slave cylinder relationship. In this case the slave is the EPA of the caliper, or your brake cylinder in a drum. But the latter is complicated due to drums having the "servo effect" but we can leave that out . Braking force comes down to a few things. As said, the bigger the disc the better the chance of slowing you down. Remember, a longer breaker bar always exhibits more force on a nut than a stubby ratchet, or your hand. This is what the purpose of the larger disc is. But of course, if you only have your finger pushing a pencil rubber onto a disc it ain't going to stop car! If you use your entire palm as well as a larger pad then you will exhibit more braking force. Likewise, a musclier person (the master cylinder) could use a bigger hand to brake the disc as opposed to a very small hand ; even he with a pencil rubber will not be able to slow down a rotating disc. Hopefully that hasn't confused you and that is a very basic way of putting it and it is how I "roughly" understand it. But it seems to fit! adam73bgt will set me straight I am sure! What is the piston size of the BMW calipers? It is a possibility for what you are saying, but the pistons would have to be around 30mm each! As for the 4 caliper arguement I am a cynic. There are benefits ; unsprung weight goes down with Ally 4 pots which helps handling and arguably braking too. Many 4 pots are less likely to flex over sliding pot calipers too which has an effect on braking power. But that said, people love the dick length factor. What sounds more impressive down the pub? "My sliding pot calipers have really improved the braking power over my 2 pot calipers" "Pffft, I've 4 pots. More is better. I've also got 19" wheels which help my handling too" Anyway, I've probably confused many people with the above but it is my take on the matter.
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adam73bgt
Club Retro Rides Member
Posts: 4,867
Club RR Member Number: 58
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That sounds about right to me Chas, I must find my braking book which breaks (ha) it all down fairly well.
Unfortunately I don't get to use the sums that much day to day so I tend to forget!
But yeah in terms of the pro's for opposed piston calipers, they're stiffer so you get improved pedal feel over a sliding caliper, you spread the force over the pad more so you can get less taper wear as the pad is pushed onto the disc in a more perpendicular fashion (this can be negated somewhat in using a twin piston sliding caliper as you spread the load more across the pad area). And they tend to be lighter as mentioned as well, plus the aesthetic value
Sliding calipers are pretty decent still in terms of performance, I mean if you have a look at the front brakes of most Jag F types you'll see they have sliding calipers (although large ones!) and my 750i had twin piston sliding calipers I believe and they could definitely bring its 2 tonne mass to a halt very sharply! while still fitting inside a 16" wheel
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the e38 calipers don't give any better performance over the iron sliding calipers. They are a little better than the aluminium early e39 sliding versions though. for calcs comparing single pot sliders with 4 pots you only add up the pistons on one half of the 4 pot.
E38 and S4 calipers pistons are bigger than most of the porsche ones, as they have to haul a huge barge down from 150
I think the lexus 430s have 4x 44mm pistons in their 4 pots, I bet they stop rather well
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the e38 calipers don't give any better performance over the iron sliding calipers. They are a little better than the aluminium early e39 sliding versions though. for calcs comparing single pot sliders with 4 pots you only add up the pistons on one half of the 4 pot. E38 and S4 calipers pistons are bigger than most of the porsche ones, as they have to haul a huge barge down from 150 I think the lexus 430s have 4x 44mm pistons in their 4 pots, I bet they stop rather well Curious why tou feel the 4 pots don't offer anything over the ATE sliders ?? You have experience with both as curious why the ATE setup utilises bigger disks instead over the 4 pots Surely due to not having as much clamping force ? So instead utilising the physics of leverage ?
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Dez
Club Retro Rides Member
And I won't sit down. And I won't shut up. And most of all I will not grow up.
Posts: 11,713
Club RR Member Number: 34
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Before you look at changing the calipers, look at changing the disc. It will have a far bigger effect on braking effort.
Our lupo was having trouble cooking the brakes on certain fast road sections, particularly if using heel and toe to keep momentum through the twisties. I could quite easily get the discs glowing orange without much effort , which ultimately lead to total brake loss as the fluid boiled.
I tried various uprated setups with little effect, in the end I just bought some g60 caliper carriers and 280mm discs, and despite my best efforts I've never boiled them again. The calipers, fluids, pads, master cyl etc are all the same, just the disc is 24mm bigger.
I figured that if all VW did when they needed a higher performance brake setup for their range was to make the discs an inch bigger, spending 100 quid on some discs and caliper carriers was a far more effective upgrade then spending 4 times that adapting some different calipers that after running the calcs only had marginally more braking effort available.
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heathrobinson
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Broken everything
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Club RR Member Number: 111
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I may have no choice Dez, if I can't get this bleedin' bleed nipple out the callipers might be fubar'd, and there's no point in me getting another set the same if I'm changing the disc size. It'd be as much work to refit a replacement of what I have as it would to fit something more common, and designed for a larger disc. I'm not averse to keeping what I have, I just think it might cost me more in the long run. I have easy access to a scrappy, and would like something with a slightly higher hydraulic advantage over what I have now, with a bit more pad on a larger disc. Don't ask for much, do I? Bigger discs are definitely a big part of changing though, If change I must. I've seen something suggesting that E38 four-pots are two 40mm pots and two 44mm pots. So effectively 1256sqmm + 1520sqmm = 2776sqmm, against the granny's 2827sqmm. Might have to look at lexus ones, as that would give me 3040sqmm of squeeze. Is there an area of car-building that isn't more complicated than you'd initially think?
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mk2cossie
Club Retro Rides Member
Posts: 2,954
Club RR Member Number: 77
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the Lexus ones would require more pedal travel for the same amount of effort with the bigger surface area. Those calc are about right from what I remember between the Granny 2pot and the E38 4pot, so thet in theory need less pedal movement for the same effort
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I'd agree with going with the biggest disc combo that would fit under the wheels, Using 280mm discs on a golf/lupo over 256mm discs with the same calipers makes quite a difference. e38 4 pots normally clamp a Diameter: 316.0 Thickness: 28.0 disc and the e39 sliders a diameter 324 thickness 30 disc. the E39 has a little less weight, but the brakes feel hugely better. However, the e38 brembos seem to be well liked on sierras, but do require a lot of clearance on the inside of the wheel, whereas you can get the same clamping force from the sliders, but with a lot more wheel fitment options. pedal travel can easily be managed through different master cylinder. the 324s will go under 17" wheels and you can squeeze huge M5 size 340mm discs under these particular 17s images.esellerpro.com/2493/I/526/3/Rim%2066.JPG The later BMWs have some huge stoppers, but the parts prices seem a lot higher, you can get the e39 stuff really cheap
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heathrobinson
Part of things
Broken everything
Posts: 848
Club RR Member Number: 111
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mk2cossie I thought that if I increase the size of the slave in comparison to the master that I get a larger amount of force, at the expense of the pedal moving further, so the larger (within reason) the slave, the bigger the squeeze, but with a longer pedal travel. Do you mean that for a given amount of push, my leg will travel further but exert a greater squeeze (note how I've learnt all the proper technical terms... )? Am I getting that right, or am I misinterpreting that somewhere? It's a long time since I did that lesson with syringes and tube in secondary school science... I'm not built like Desperate Dan, but I am fairly lanky, so a bit of extra movement ain't an issue if it stops me harder given my available leg effort, within reason. legend, those e39 stoppers are dirt cheap on the bay of Eee, and are so close to the granny callipers it's shocking! 60mm dia pistons too, even the bolt spacing seems similar from what I can find. The main advantage is that they're actually available at a reasonable preice, whereas the granny ones are either way to pricy or a ball of rust. They are looking like the way forward. With the Lexus jobs being 42mm pistons, their advantage has pistoff, so to speak. That'd give 2770sqmm of piston face against the E39/granny's 2827sqmm. The pad face isn't vastly different - 54mm x 115mm on the lexus and what I'm guessing is pretty much identical on the granny as their overall dims are 58mm x 156mm, which is surprising - I thought that the 4-pot callipers would be longer. The beemer pads look quite a bit larger, at 73mm x 156mm, although I'm not sure if that's a total dimension or just the effective pad size. Either way, they look to be a lot deeper than the other two.
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Oh and I have a few spare sets of BMW brembos here if you go that route too
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yep, bigger slave, bigger clamping force at the expense of longer pedal travel, bigger dia master then pedal effort goes up but travel goes down.
I have some of the early aluminium e39 calipers that fit the 316 discs you could have for the cost of postage. Postage would be a bit as they are still quite heavy/
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Mk3 Mondeo calipers with st170 discs were perfect for my mk4 escort. My escort was originally a 1.4 and after fitting the 300mm discs, the first drive was weird as I could feel the weight of them as I pulled away lol
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chubz
Part of things
Posts: 339
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Feb 20, 2017 14:22:33 GMT
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mondeo/focus st170 calipers with 300mm discs will also fit under 15'' wheels if you shave the outer edge of the caliper
good upgrade for sure
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