D2 BBK ordered.....2-5 week wait tho : (
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You've ordered 356mm for front & rear?Jonny essex said:
Have you checked about the brake bias with this setup? There's a good reason that the OEM rear brakes are smaller than the fronts...
Also worthwhile confirming that the handbrake will still function correctly with this kit, as a number of people have reported problems with getting the handbrake to work effectively with BBKs
Jonny essex said:My rears are currently are only 15mm smaller, with the rears on the BBK only a 4 pot with front a 6 pot i cant think of any issues with balance under breaking.PerryGunn said:
Plus the kits retain the handbreak function
It's not really about 'thinking' though Jonny, or about the size difference, it's about knowing. Hopefully you've taken advice from the person who is installing it for you ?
Like your intended set up - brake bias will be important so I'm pleased it was brought up and you've checked.
I think the D2 set up will look brilliant (I think the standard discs on my 3.0si look small - especially rears). It's going to be useful too when you upgrade your power unit.
Looking forward to the photos when fitted
(PS - it's brakes not breaks)
:driving:
I think the D2 set up will look brilliant (I think the standard discs on my 3.0si look small - especially rears). It's going to be useful too when you upgrade your power unit.
Looking forward to the photos when fitted
(PS - it's brakes not breaks)
:driving:
Jonny essex said:My rears are currently are only 15mm smaller, with the rears on the BBK only a 4 pot with front a 6 pot i cant think of any issues with balance under breaking.PerryGunn said:
Plus the kits retain the handbreak function
simply if your rears are equal or brake more (think about weight distribution) than the front your car will become unstable under braking. in bad cases it will simply make the car swap ends. think of how easy it is in a go cart to make it spin under braking.
a simple proportioning valve will solve this.
im sure youve done the research so was there anything you had to do to the master cylinder i.e make it bigger as the volume of fluid being moved is greater? when you do your mega engine swap maybe consider going to a 2 master cylinder setup with a bias bar between them?
Thinking the brake balance will be OK isn't really good enough - what you have to remember is that the brakes don't stop the car, the tyres do!
Each tyre has a maximum amount of braking force that it can apply through it's contact patch, this is dictated by the weight over the tyre and the coefficient of friction of the rubber, if you exceed that amount the wheel will lock and the tyre will slide. Assuming identical tyres all round, in a car like the Z4 the front tyres are capable of generating greater breaking forces than the rears because you have the weight of the engine over the front axle plus the additional weight transfer forward during the braking process, this is why you tend to have bigger brakes on the front - for the same pad size bigger rotors are capable of applying more ft/lbs of torque.
The art with brakes is to balance the system so that all tyres are exerting roughly the same percentage of their maximum braking force when you hit the pedal - this doesn't mean that the amount of retardation at each wheel is the same just that when the fronts are at 25/50/100% of maximum retardation so are the rears. If you don't do this correctly you could end up with a situation where one set of tyres is locking up whilst the other set is comfortably within it's limits - best case is longer stopping distances (not what you expect from bigger brakes), worst case is loss of control and unexpectedly ending up in a hedge/wall/ditch...
Each tyre has a maximum amount of braking force that it can apply through it's contact patch, this is dictated by the weight over the tyre and the coefficient of friction of the rubber, if you exceed that amount the wheel will lock and the tyre will slide. Assuming identical tyres all round, in a car like the Z4 the front tyres are capable of generating greater breaking forces than the rears because you have the weight of the engine over the front axle plus the additional weight transfer forward during the braking process, this is why you tend to have bigger brakes on the front - for the same pad size bigger rotors are capable of applying more ft/lbs of torque.
The art with brakes is to balance the system so that all tyres are exerting roughly the same percentage of their maximum braking force when you hit the pedal - this doesn't mean that the amount of retardation at each wheel is the same just that when the fronts are at 25/50/100% of maximum retardation so are the rears. If you don't do this correctly you could end up with a situation where one set of tyres is locking up whilst the other set is comfortably within it's limits - best case is longer stopping distances (not what you expect from bigger brakes), worst case is loss of control and unexpectedly ending up in a hedge/wall/ditch...
My understanding about 2 pot 4 pot and 6 pot brakes is limited.... And mostly from a MTB background..
But the number of pots dose not actually add more power? But gives better modulation of power. The pistons are after all operated from the master cylinder and your foot.
What the larger number of pistons can do is potentially add a more even force over the pad - disc contact area giving a better feel???
But the number of pots dose not actually add more power? But gives better modulation of power. The pistons are after all operated from the master cylinder and your foot.
What the larger number of pistons can do is potentially add a more even force over the pad - disc contact area giving a better feel???
Machine monkey said:
there is also the question of contact point. i.e the force can only be transfered vis the contact of the pistons with the pads. if the 4 pots area = less than whats there then there will simply be less force transmitted.
brakes pose loads of great questions and swapping them needs consideration. its worth looking into as it can be quite interesting. things like over cooling, unsprung weight, biasing. its not a simple bigger is better formula
my westy uses sierra 1.8Lx front brakes. sounds pathetic, looks puny, but were designed to stop a 1.8T jelly mold. therefore have no problem with the 325kg axle weight. i would get better feel if i swapped to solid discs from vented. 4 pots would reduce unspring weight, the solid discs wouldnt cool as well as the vented. i could probably achieve a similar increase in performance by getting some groved drilled ones and different pads. interestingly some of the more successful race guys still use drum rear brakes over a disc
Machine monkey said:
It's the total piston area that amonts to the clamping force (pressure x area = force). They use more brake pods to spread the load evenly (brake pads flex).
The larger the pad (compared to the pot) the more the need to spread the load (and use more pots).
But most speculation here about brake bias won't be any problem. The z4 is so much front biased, that you'd have to do very strange things to get it rear biassed.
Ontopic: I'd gone with floating discs, especially at the front (better brake feel, lighter disk because of aluminium center etc), and for the rear i'd gone with 1 size smaller disk than the front (again for unsprung mass reduction). Keeping your unsprung and rotational mass as low as possible gives a performance benefit in multiple ways (both a acceleration gain as a handling gain). Rear brake force is something there's almost always enough off (rear brakes hardly get hot compared to the fronts).
Unless you install them for the looks of course, then decide on what looks best in your eyes
Jonny essex said:
not at all. (well im not) i was more interested in what the knock on effect of changing the calipers would be. my other experience is that its not a simple case of bigger=better as there is more to it than. e.g i wanted to go to wilwood 4 pots. all round. it would reduce my unspring weight (worth considering for your application although i would specualte the BBKs are made of lightweight stuff to compensate for this) but the flip side was it would increase my pedal travel as more fluid would be displaced in the system. to compensate for this i would need to change my master cylinder and move the pivot point of my pedal (both easilly done on that car) but moivng the pivot point would then change the force i was applying on the pedal .....
i was also pointing out that if you had the same braking force at both the front and back (guidoc has answered that) you would also be getting some odd handling again solvable using either a bias bar or simply using shitty pads at the back. at the end of the day your rear brakes really dont do loads of braking and do alot to keep the front of your car at the front when you do brake
for a laugh to see how it was i purposely made my rear brakes lock before the front. it was scary and unpredicable but mostly the car wanted to swap ends at any given point during braking
Jonny, I don't think anyone is offering anything other than good advice. I certainly wasn't having a pop, or St least I didn't intend to. I know nothing about brakes in the way others on this thread do, but I know it's not as simple as just slapping them on. Assuming you've done your research and spoken to your mechanica nd have bought on the basis of knowing what else needs done, it's all good
I fitted my Ksport 8 pots today on my zed, although i'm still in the process of bedding them in i can say honestly...just wow!. this is how a zed is meant to stop!, the pedal feel and modulation is massively confidence inspiring and i now feel i can take the car by the scruff of the neck and DRIVE it instead of semi consciously planning ahead thinking 'can i stop?'...no brake balance issues either. Anyway, sorry for the hijack, mini review over. 
Jonny essex said:
How are they going to tweak though, not a lot you can do unless a bias is being fitted. As above though if this is the setup that has been recommended then fine, but assuming they will be ok because there is 2 pots less on the back could be a mistake.
I think you're all blowing things waaaay out of proportion to be honest!... anyone is welcome to come and have a quick go in my car with these new k sports on and just see what a difference there is in stopping power. I'm a newbie on here and a newbie to the z4, but i'm in no way a newbie to building and setting up cars of all kinds with a strong history of track driving and if i thought for a second i was putting myself or others on the road in danger i would'nt of fitted these brakes in the first place!.... if anyone on here can honestly tell/feel a major brake imbalance (to the point where it feels dangerous) on public roads then i'd say you're driving in a fashion which is only going to end badly.
