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BIG BRAKE KITS - The truth is out there....

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Hi all - so along with my other post I have been researching BBKs. 

 

Before I go on - I am 100% sure this has been posted and discussed millions of times online - But I was hoping I could get some clarity to my thoughts....

 

So I will write some stuff - and please feel free to discuss, correct contradict etc etc. What I am keen to ascertain is a sound engineering technically correct answer - not based on opinions or what is "felt" when driving.

 

So, as per I have been advised in other posts I should uprate the brakes BEFORE adding power. It seems logical but the question is WHY. 

 

Lets make some assumptions first.

 

I already have good quality sport tyres on the car and we are driving in a spirited fashion down a country road and we have to deal with either of the 2 situations. 

1. An emergency stop

2. Continued braking performance for the duration of the run.

 

Now, the primary and "perhaps only" reason to upgrade to a BBK is their ability to deal with the heat that is being generated hen braking and continue to function at optimal performance.

 

Given this statement - I am not convinced there is any reason to fit a BBK to a street car?? TBD.

 

In situation 1 above - the limiting factor of the stop is the grip of the tyres as the OEM brake set up will easily engages the ABS and without ABS it would easily lock the wheels. This means the brakes are stopping the car in as short a space as possible and a BBK would not offer any advantage.

 

In circumstance 2 - I am not quite sure I believe that you could be driving hard enough, for long enough, on a road where the corners are close enough to reach and exceed the operating parameters of the OEM set up. obviously as you brake hard into corners the heat generated will be extreme, but as soon as you are off the brakes they begin to cool and are ready for the next corner and unlike a track that corner is likely someway down the road.

 

There is also an argument whereby fitting them is actually a detriment due to un-sprung weight etc etc. Not to mention the huge cost....

 

I think perhaps people are somewhat "tricked" (I am not being cheeky here) as the BBKs feel better and give some sort placebo......

 

For the record - I want a BBK and I think they are cool...... but the engineer in me wants the right answer..... :)

 

Thanks to anyone willing to contribute

 

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29 minutes ago, stubobby said:

Hi all - so along with my other post I have been researching BBKs. 

 

Before I go on - I am 100% sure this has been posted and discussed millions of times online - But I was hoping I could get some clarity to my thoughts....

 

So I will write some stuff - and please feel free to discuss, correct contradict etc etc. What I am keen to ascertain is a sound engineering technically correct answer - not based on opinions or what is "felt" when driving.

 

So, as per I have been advised in other posts I should uprate the brakes BEFORE adding power. It seems logical but the question is WHY. 

 

Lets make some assumptions first.

 

I already have good quality sport tyres on the car and we are driving in a spirited fashion down a country road and we have to deal with either of the 2 situations. 

1. An emergency stop

2. Continued braking performance for the duration of the run.

 

Now, the primary and "perhaps only" reason to upgrade to a BBK is their ability to deal with the heat that is being generated hen braking and continue to function at optimal performance.

 

Given this statement - I am not convinced there is any reason to fit a BBK to a street car?? TBD.

 

In situation 1 above - the limiting factor of the stop is the grip of the tyres as the OEM brake set up will easily engages the ABS and without ABS it would easily lock the wheels. This means the brakes are stopping the car in as short a space as possible and a BBK would not offer any advantage.

 

In circumstance 2 - I am not quite sure I believe that you could be driving hard enough, for long enough, on a road where the corners are close enough to reach and exceed the operating parameters of the OEM set up. obviously as you brake hard into corners the heat generated will be extreme, but as soon as you are off the brakes they begin to cool and are ready for the next corner and unlike a track that corner is likely someway down the road.

 

There is also an argument whereby fitting them is actually a detriment due to un-sprung weight etc etc. Not to mention the huge cost....

 

I think perhaps people are somewhat "tricked" (I am not being cheeky here) as the BBKs feel better and give some sort placebo......

 

For the record - I want a BBK and I think they are cool...... but the engineer in me wants the right answer..... :)

 

Thanks to anyone willing to contribute

 

Upgrading brakes is very long stretched term. 3 main questions before anything should be: how good is current brake setup? Do they get overheated often, if not, most likely they are not on limits so far. Next question, what will be power target? If not huge gains, like doubling factory power output, most likely brakes will handle that, if they were fine so far.

And third question: what purpose car mainly will be used for? If mostly track days or other sport events, you might think about more effective setup. If it's everyday street car. Most likely you won't be driving to limits most of time, unless your license has won on lottery.

 

Very noticeable difference always can be reached just with choosing more aggressive brake pads, brake discs, and fresh brake fluid. About pads need to be careful when choosing for daily car, because some brake pads have quite bad braking performance until brakes will reach some temperature, or some of them are very noisy when cold, which again can be very annoying on daily car. 

 

In my opinion there's a lot of things to consider before spending thousands on big calipers, because sometimes there can be more downsides than benefits, all depends on car and what's it's purpose. Those are just my own thoughts, some will agree, some disagree. But that's what discussion is made for:)

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4 minutes ago, Ray112 said:

Upgrading brakes is very long stretched term. 3 main questions before anything should be: how good is current brake setup? Do they get overheated often, if not, most likely they are not on limits so far. Next question, what will be power target? If not huge gains, like doubling factory power output, most likely brakes will handle that, if they were fine so far.

And third question: what purpose car mainly will be used for? If mostly track days or other sport events, you might think about more effective setup. If it's everyday street car. Most likely you won't be driving to limits most of time, unless your license has won on lottery.

 

Very noticeable difference always can be reached just with choosing more aggressive brake pads, brake discs, and fresh brake fluid. About pads need to be careful when choosing for daily car, because some brake pads have quite bad braking performance until brakes will reach some temperature, or some of them are very noisy when cold, which again can be very annoying on daily car. 

 

In my opinion there's a lot of things to consider before spending thousands on big calipers, because sometimes there can be more downsides than benefits, all depends on car and what's it's purpose. Those are just my own thoughts, some will agree, some disagree. But that's what discussion is made for:)

 

so for my own car - i am looking to one day supercharge it - so going from 230bhp to 350bhp.... one day - not yet.

 

my aim is to make a cross country sports saloon for my own pleasure which i am sure i will take on track at some point but it will be rare.

 

I think the brakes are big for the car - 324mm up front. Worth noting that a M5 e39 only has sliding 1 piston caliper.

 

i think your comments are all valid and everything I would consider - but i am hoping someone can actually comment with technical calculation?? I hope.... and thus prove one way or another

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The maths of it must relate to leverage - the bigger the disc the further out the pad and so the bigger the force to stop the rotation so one could stop the disc with less pedal effort or perhaps modulate the pressure better?

 

Thickness i think relates to heat soak and dissipation though of course a greater diameter will add to that capacity too,

 

I understand your point of if you can lock the tyres/ trigger ABS that's all you need. ie you can't do any more that that.

 

My experience running e34 M5 brakes on my e28 was that before i fitted them i could feel a degradation in performance with repeated stops when pushing on where say you have a number of roundabouts connected by dual carriage way so some big stops/ speed reductions needed in quick succession. With the bigger brakes better able to deal with the heat i never had an issue and nor did they ever fade on track days when they got a proper work out.

 

I suggest day to day a standard car would never get its brakes hot enough for any of this to be an issue but a faster car will potentially be stopping from higher speed so making more heat and thus more likely to get to the limit of the standard brakes envelope of performance.

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From an every day driving perspective, IMO, BBKs look cool, but are overkill when decent discs, pads, braided lines and fluid can make an OEM braking set up so much better. 

 

Having a daily driver that does the odd track day is also under sufficient braking with the above, IMO, but maybe more aggressive pads and a different set of alloys with track day specific tyres to be used etc. 

 

For a road legal track day car, a BBK is worth its weight in gold IMO, but that's because of the heavy brake use and the need of much more aggressive compounds and cooling requirements etc. 

 

I've had BBKs fitted to previous cars (Integra DC5, CRX, Evo VI etc) but they did a lot of track days, I've wanted to fit a BBK to my previous E39 and would love to fit one to my touring, but it'd be for aesthetics more than anything else and for me, that's a lot of moolah simply for looks... 

 

Horses for courses 

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If target power is around 350hp, most likely you will be absolutely fine with stock size brakes, just need to use some good quality, more aggressive  discs and pads. Another story if you want bigger brakes to look better, that's a different thing.

So most likely decision is yours to make. And you still can upgrade them any time after it's supercharged, and if you feel that brakes are not good enough.

My mate has built turbocharged e46 with over 700hp running on e85, he's still on biggest stock E46 brakes (not M3) with Ate power discs and pads. Not complaining about stopping. Ok, it's lighter car, but at the same time it's twice more power than you are planning.

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Yes, fresh OEM disc with a good pads (EBC colourful stuff, DS2500, etc) will go a long way to improving the E39 brakes. Bigger rotors are even better, but, as has been mentioned, I don't see much point in larger calipers off the track.
 

I don't think an argument of power makes much sense as these are heavy cars; even a 520i can be cruising at 80 mph and still have an idiot pull out on them.


Before COVID, I was driving a lot of new rentals with work. None handled anywhere near as nicely as the E39 (actually the new A4 was pretty good, but we wont get into that), but almost all had better brakes.

By modern standards and for a car of its mass, the E39 is way under braked and the stock pedal feel is not great. This is even more of an issue with cars that have the 298 mm up front. The 324 mm is ok, but the 345 mm is noticeably better (emergency stop and continual braking). Note that the M5's 345 mm is still smaller in diameter than a 2009 520d (348 mm).

If you can fit a larger diameter disc, do. The calipers on the 324 mm and 345 mm are the same (bar the expensive M logo), so you only need to change the carriers. If you are not going with floating rotors, it's not that expensive and upgrade. Rear brakes are another more expensive story. Although, @V8Warrior has a nice video on this.

As for pedal feel, braided lines help, a bit. Honestly though, I struggled to feel a difference between braided and fresh OEM lines (sure, there is a hell of a difference with old baggy lines). I think a better argument for braided is that PTFE is not going to swell and they are very, very, hard to damage. Swapping out the master cylinder for an E65/66/67 unit (34336785926) will make a bigger improvement. There's a lot on this in the m5board. Note, all E39s with DSC share the same master cylinder (34311165544), 520i to M5, and all have a soft pedal feel compared to something more modern.
 

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1 hour ago, sinner said:

Yes, fresh OEM disc with a good pads (EBC colourful stuff, DS2500, etc) will go a long way to improving the E39 brakes. Bigger rotors are even better, but, as has been mentioned, I don't see much point in larger calipers off the track.
 

I don't think an argument of power makes much sense as these are heavy cars; even a 520i can be cruising at 80 mph and still have an idiot pull out on them.


Before COVID, I was driving a lot of new rentals with work. None handled anywhere near as nicely as the E39 (actually the new A4 was pretty good, but we wont get into that), but almost all had better brakes.

By modern standards and for a car of its mass, the E39 is way under braked and the stock pedal feel is not great. This is even more of an issue with cars that have the 298 mm up front. The 324 mm is ok, but the 345 mm is noticeably better (emergency stop and continual braking). Note that the M5's 345 mm is still smaller in diameter than a 2009 520d (348 mm).

If you can fit a larger diameter disc, do. The calipers on the 324 mm and 345 mm are the same (bar the expensive M logo), so you only need to change the carriers. If you are not going with floating rotors, it's not that expensive and upgrade. Rear brakes are another more expensive story. Although, @V8Warrior has a nice video on this.

As for pedal feel, braided lines help, a bit. Honestly though, I struggled to feel a difference between braided and fresh OEM lines (sure, there is a hell of a difference with old baggy lines). I think a better argument for braided is that PTFE is not going to swell and they are very, very, hard to damage. Swapping out the master cylinder for an E65/66/67 unit (34336785926) will make a bigger improvement. There's a lot on this in the m5board. Note, all E39s with DSC share the same master cylinder (34311165544), 520i to M5, and all have a soft pedal feel compared to something more modern.
 

Sinner

 

thanks for the post - whilst we've still not got to the technical answer I am curious for - I really appreciate your input as it gives me some realistic upgrades that will improve things. and they come without significant cost.

 

What it is all driving towards is that the braking system is still going to overheat before reach the limiting factor of the tyres - which I am not convinced about - other than severe prolonged use. Good feel doesn't always translate to an improvement in stopping distance though....

 

So - I have opted for Stoptech discs and pads and I have already has my callipers refurbished and painted so I would be reluctant to go for the 345 upgrade as I've already spent some cash - but I will bare it in mind for when  they need done. 

 

I am interested in the master cylinder upgrade you mentions - do you know if its a direct swap.

 

thanks so much

 

as a final note - I am still puzzled by the fact that you say modern brakes are way better but the limiting factor in a one stop emergency is tyre grip so why have braked gotten bigger and what is it doing for us....

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I think your engineering intuition is generally correct, and I agree with what is being said here.

 

Point 1 - I think if you experiment you'd find at high speeds you don't engage the ABS quite so quickly even if you would at low speed. The inertia of the wheels is significant enough to keep them going round fighting the brakes. That's where some extra braking torque of bigger brakes could be used. Particularly in modern cars that tend to have bigger heavier wheels. Also like Duncan says - feel and modulation. I think these factors are why modern cars have bigger brakes and feel 'better' even though your old car with small brakes can easily engage the ABS at lower speeds.

 

Point 2 - not sure where you live, but try a spirited drive through Milton Keynes! :) Reach 80-90, slam on the brakes for a roundabout, rinse and repeat. In my previous car - 3.0 Vauxhall Omega - I'd have significant brake fade and have to go easy way before getting through town! Never done it, but expect a similar story on the E39, although I think the 530 brakes would be a little bigger than the Vauxhall's. That kind of punishment really shows up the weakness of stock brakes on a heavy car! Better discs and pads would go a long way there, but bigger would be better too.

 

Probably not a concern for you, but is for me now I'm in Norway - my 530 is shit in snow on my old 17" staggered wheels so I wanted smaller for winters. I cant go any bigger than the current 530 brakes with my 16" winters. Something to think about if effective winter driving is a concern.

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47 minutes ago, Liam79 said:

Point 2 - not sure where you live, but try a spirited drive through Milton Keynes! :) Reach 80-90, slam on the brakes for a roundabout, rinse and repeat. In my previous car - 3.0 Vauxhall Omega - I'd have significant brake fade and have to go easy way before getting through town!

 

^This

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On 27/12/2020 at 17:16, stubobby said:

 

so for my own car - i am looking to one day supercharge it - so going from 230bhp to 350bhp.... one day - not yet.

 

my aim is to make a cross country sports saloon for my own pleasure which i am sure i will take on track at some point but it will be rare.

 

I think the brakes are big for the car - 324mm up front. Worth noting that a M5 e39 only has sliding 1 piston caliper.


My E93 weighs 1800kg & puts out 300bhp as standard with the same torque as the M3 but also just has big single pot sliding caliper. 
 

Our Cerbera is only just over 1000kg has huge AP racing 4 pot calipers & discs with separate bells & rotor, but we have still boiled the the fluid on track. 
 

On the road there isn’t any noticeable difference between them. On the other hand I have no intentions of spending a full day thrashing the E93 round on a track day. 
 

The 530i did have average brakes till I put new standard discs & pads all round, refurbished the calipers & fitted braded lines & hard lines. That transformed it & for normal road use it feels every bit as good as the other two now. 
 

One other point to consider about supercharging is insurance. I was just chatting to them about how much it would be if I remapped my 335i up to 400bhp, only about £50 more as its not a huge increase. They did say a guy had just supercharged his M3, it would have been about £300 (same as my 335i) but with the supercharger it was going to be £700! 
 

If you’re ok with higher premiums I should look into the turbos off an N54, it’s just the next version of the M54, I just had mine off for new waistgates & the exhaust ports looked very much like they could just bolt on:

 

nYb5KLU.jpg
 

Of course you’d still have the oil & water pipes to workout as well as exhaust & inlet, so a supercharger is probably easier! 
 

Edit - I forgot to add after rebuilding the calipers & fitting braided flexibles the pedal feel was much improved. Not sure which made the most difference as I did them all at the same time!

There is a special bleeding sequence you need inpa to do, I did that too, not sure it it helped also...

Edited by Andyrt200
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30 minutes ago, Andyrt200 said:


My E93 weighs 1800kg & puts out 300bhp as standard with the same torque as the M3 but also just has big single pot sliding caliper. 
 

Our Cerbera is only just over 1000kg has huge AP racing 4 pot calipers & discs with separate bells & rotor, but we have still boiled the the fluid on track. 
 

On the road there isn’t any noticeable difference between them. On the other hand I have no intentions of spending a full day thrashing the E93 round on a track day. 
 

The 530i did have average brakes till I put new standard discs & pads all round, refurbished the calipers & fitted braded lines & hard lines. That transformed it & for normal road use it feels every bit as good as the other two now. 
 

One other point to consider about supercharging is insurance. I was just chatting to them about how much it would be if I remapped my 335i up to 400bhp, only about £50 more as its not a huge increase. They did say a guy had just supercharged his M3, it would have been about £300 (same as my 335i) but with the supercharger it was going to be £700! 
 

If you’re ok with higher premiums I should look into the turbos off an N54, it’s just the next version of the M54, I just had mine off for new waistgates & the exhaust ports looked very much like they could just bolt on:

 

nYb5KLU.jpg
 

Of course you’d still have the oil & water pipes to workout as well as exhaust & inlet, so a supercharger is probably easier! 
 

Edit - I forgot to add after rebuilding the calipers & fitting braided flexibles the pedal feel was much improved. Not sure which made the most difference as I did them all at the same time!

There is a special bleeding sequence you need inpa to do, I did that too, not sure it it helped also...

 

Thanks for post... useful and welcome.

 

SO.....

 

calipers rebuilt and and factory fresh courtesy of biggred - CHECK

new Stoptech slotted discs and pads - CHECK

braided lines - CHECK....

 

will add some pics

 

might do the master cylinder as recommended earlier

 

they'll probably make it onto the car in a year or so :)

 

as for the SC - not concerned about insurance as it wont be a daily so will just put up with it - see my other post ref rebuilds

 

 

 

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ESS supercharger?

 

17 hours ago, stubobby said:

 

they'll probably make it onto the car in a year or so :)

 

 

Oooh careful with those long term plans! I had those... then suddenly you have three babies and they are 'on hold'! :)

 

Get it done while you still can! :lol:

 

EDIT: Ah I just seen from your project thread it already happened and you're on the other side! :) Maybe hope for me?

Edited by Liam79

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On 07/01/2021 at 08:16, Liam79 said:

ESS supercharger?

 

 

Oooh careful with those long term plans! I had those... then suddenly you have three babies and they are 'on hold'! :)

 

Get it done while you still can! :lol:

 

EDIT: Ah I just seen from your project thread it already happened and you're on the other side! :) Maybe hope for me?

 

yeah - hopefully ESS

 

havent even been back out in months now - but to be fair its super cold up here

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