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      05-01-2009, 03:26 PM   #1
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Best value BBK on sale?

Hi hi

Im currently looking into some new, namely more powerful brakes (front and rear) seeing as I plan to be hitting the 'Ring a couple of times this summer. Also would like to see some nice bigs rotors filling the emptiness of my 19's!

The ones I've looked into are:

BMW Performance BBK - 1125
Brembo GT 380x32 & 345x28 - 6000
Tarox 350x30 & 345x20 - 4500
StopTech 355x32 - 4900

Apart from the obvious price/OEM advantage, I have read positive reviews of the BMW BBK on here and nothing really that wrong with them. Even if I were to replace the hoses and pads after purchasing the BBK, it would still be more than half the cost of the others!

But am I missing something? I know the BMW BBK is from Brembo anyway, so why the massive price hike? Even the smaller diameter official Brembo BBK are about 5000!
Would they generally last longer than the BMW pads/discs?

Would be good to hear from you guys on this, seeing as you are generally more informed on the flesh and blood of E9x's. Has anyone any better suggestions or had experience with other brakes?

Thank you please!
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      05-01-2009, 05:52 PM   #2
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Well, I'm half caked, having been to a wedding all day, so excuse any misspelling, but I can vouch for the BMW Performance Brakes, with standard BMW brake pads, as Ant @ Speed Religion took me out in his 330d last week with this set-up, the brakes are unbelievable, I was amazed by them. For the price I thought they were great. I can't imagine how paying upwards of 6k would improve by any recognisable amount. Bed-time now...
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      05-02-2009, 07:30 AM   #3
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Hey mate, thanks for the quick reply with your 'DUI' type situation

I've heard the same about the BMW BBK. I just want to know why its significantly cheaper/ why the others are significantly more expensive..
The BBK is starting to look like a no-brainer though
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      05-02-2009, 09:23 AM   #4
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The BMW BBK system is undeniably good value - 6pot Brembo calipers at the front, 4pot rears, drilled discs, different pads. For the money, it's unbeatable

However, you have asked a very valid question as to why they are so cheap. The thing with 6pot brakes is that across the range there is a HUGE variation in quality and performance.



Firstly, it would be an idea to understand a little bit about the design of multiple-pot calipers and the advantages/disadvantages of certain systems.


Generally, and in the most simplistic view, the most important aspects of a brake caliper design are -

a) the technical suitability of the caliper force in relation to the target vehicle
b) how evenly it distributes braking force across the entire face of the pad,
c) the heat resistant capability of that caliper in terms of the way it can dissipate heat away from the pads,
d) the long-term durability and reliability of the caliper
e) weight


There is a common misconception that the greater number of pots the better the braking system. A bigger set, or a greater number, of caliper pistons will provide more clamping pressure on that axle, but could also have a negative effect on total brake performance. If the pistons are too large for the application it will lead to excessive pedal travel and the front/rear brake balance will be adversely affected, resulting in longer stopping distances. Clamping forces can also become so strong that you'll end up locking the brakes far too early, making brake modulation and control very difficult.

In reality, the number of pots is not as important as the technical design and setup of each caliper to a particular vehicle. In the most simplistic terms, the greater the number of pistons/pots, the greater the surface area of pressure being applied to a brake pad, and hence the greater amount of friction generated (assuming the brake pad characteristics haven't changed in the comparison). However, it is more important that the correct braking force is distributed along the pad - having a more efficient 4pot system valved correctly for the vehicle will give much better braking performance than an oversized 6pot caliper with mismatched valving.

A larger brake caliper normally leads to using larger-sized pads - however, just because a pad is larger doesn't mean that there is more braking force. A bigger pad of the same compound in the same location as a smaller pad will not actually give shorter stopping distances. The stopping force or torque reaction is derived from the pad friction coefficient, the diameter of the brake disc and the amount of pressure applied. A bigger pad does not apply more pressure, only the same pressure over a bigger area. The advantage of a bigger pad lies in its heat capacity and rate of wear - the larger the pad, the more it will be able to absorb initial heat, thus suffering less thermal shock and with the consequent advantage of greater pad life.

However, there are sometimes problems with having larger pads - the popular Porsche calipers use a taller pad than most other systems, and whilst this taller pad gives slightly better heat characteristics, the system actually requires a heavier brake disc to match. This heavier disc has greater inertia and if the piston valving pressure is not adapted to suit, you actually end up with longer braking distances.

Piston/caliper design is also important - the cheaper calipers generally use stainless steel or aluminium alloy pistons coupled with simple dust boots, and are almost always of a two-piece cast aluminium design. The most expensive calipers may use titanium pistons (lighter and stronger), with much better high-temperature dust seals on each piston. They may also be of a forged monobloc design, which if designed using the correct alloys may well be stronger than a regular caliper, but may not necessarily be stiffer. A big brake kit will provide increased heat capacity, which means substantially more resistance to brake fade and caliper distortion with multiple stops from high speed. The stronger the caliper, the less the distortion and the more precise the braking performance. It will also give a firmer pedal due to stronger and stiffer components, as well as better modulation characteristics. The lighter the caliper the greater the reduction in unsprung weight, which will yield better handling and suspension characteristics on a properly setup car

Some calipers also use a differential bore design, in which smaller pistons are used up front, with larger pistons at the trailing edge of the caliper. As the surface of the brake disc heats up, the clamping force of the pistons has to be increased to maintain braking force (due to increasing fade). If the caliper has multiple pistons (or multiple pairs of pistons), the brake disc surface is initially heated by the pistons pushing against the brake pad at the leading edge of the caliper, making the disc surface hotter when it rotates back to the pistons closer to the trailing edge of the caliper. Therefore it helps if the pistons closer to the rear edge of the caliper are larger as they can deliver greater pressure.



So, with all that in mind then, why's the BMW BBK such good value?

Pros
Well, it's a basic 6 pot system (front), designed by Brembo as a two-piece aluminium caliper. It uses inexpensive standard compound Jurid/Textar brake pads (which are the regular BMW OEM pads), with basic one-piece drilled & slotted 338x26mm discs, simple individual piston dust seals and standard BMW brake hoses.

Because the caliper, and entire brake system, was designed as an OEM piece for the 135i, BMW have managed to drive the cost of that caliper down and hence can pass on the savings to the aftermarket customer. The only difference is the brake disc, which on the Performance kit is the same intrinsic disc but now drilled and slotted. The ancillaries have also been built down to a price - this is not being disrespectful to BMW, but in reality you can't imagine BMW using a 1500 brake system as standard on the 135i. For regular road use and as a standard no-thinking-required replacement for standard brakes it's a very good kit. The vast majority of BMW drivers would be very happy with this BBK as it's a fit-and-forget system And compared to the brakes on a 325i (not so much to a 335i/d) it's a vast improvement.


Cons
However, when you start exploring the higher limits of the BMW BBK there are several failings that become obvious. Firstly, it is next to impossible to get aftermarket pads for that caliper - because it's a BMW-specific caliper and not a standard Brembo shape, the likes of Pagid and Ferrodo have been very slow in developing aftermarket pads for that application. The regular BMW pads are ok for road use, but on the track they start to fade and judder very quickly. The more aggressive driver or track-day enthusiast will probably find the limits of the pad quite quickly. To be able to change to Pagid race pads for use on a track for example might be very important and necessary. Continuing this theme, it isn't easy to change the pads on the BMW BBK - the caliper has to come off. Compare that to the top-end Brembo kits where the pads are held in by quick-release pins and you can do a pad change in mere minutes.

The brake discs are one-piece items with integral bell (the bit that holds the disc onto the hub). There's no way to improve the brake disc by using aftermarket items from the likes of Performance Friction (who make arguably the world's best brake discs). The standard discs themselves also aren't as heat-resistant as they could be and will warp more easily under duress. The heat characteristics of the pistons also leave much to be desired - when out on track, under duress the pistons have a tendency to crack, whilst the seals will almost certainly disintegrate. This has been shown many times now on the 135i race cars. The caliper also displays quite uneven pressure distribution across the pistons - the last set of pads I used on my BMW BBK were noticeably warped with a 3.5mm height difference between the widest edges.

These problems only showed up when the brakes were put to more serious use. I discovered all this first hand at the Nurburgring last summer, when I subjected the brake system to only a moderately torturous test I was actually disappointed at how spectacularly the calipers failed I was reminded though that they are also spectacularly cheap and not really designed for that sort of abuse!! To BMWs credit they replaced that first kit with a new set of calipers..!

On normal road driving, the limits would not be anywhere close to being reached and so I would still recommend them as a significant performance upgrade to the standard brakes on anything up to a 330 (pre-LCI) under these conditions

I would NOT recommend the BMW BBK for someone with a 335i or 335d, or with an LCI 330i or 330d, as there are too many disadvantages going to the BBK compared with the regular OEM setup - the main problem is the discs are much smaller and thinner and can't absorb anywhere near the amount of heat that the OEM discs can




My thoughts


If you are looking to use the car on a track on more than the odd occasion, or do LOTS of high-speed driving, then I would suggest you look at a higher-spec alternative. There has been mention of the 4000/6000 Brembo GT kits etc, which are fabulous but massively over-specced for use on anything other than fully-fledged race cars.

The Tarox kits have issues of their own - the cheap kits are exactly that - cheap and nasty. The 12pot systems are ridiculously expensive, and to be honest why on earth would anyone need a 12pot system? The individual pots themselves are tiny, the weight of the caliper is huge, and the performance doesn't justify the price.

Probably the best value kit, and the one I'm now using to great effect, is the AP Racing 6pot front / 4pot rear system. The front 6pot system is a two-piece cast aluminium design using 355x32mm slotted and vented discs with separate bells, aluminium alloy pistons with individual high-temp dust seals and comes supplied with mounting brackets, braided hoses, Ferrodo DS2500 fast-road pads, and Dot 5.1 brake fluid.

The rear system uses a 4-piston version of the same caliper, Ferrodo DS2500 pads, but uses the standard rear BMW OEM discs. I believe that Stillen Racing in the USA have a different version of the rear AP system that uses replacement discs as well.

I have been using the APs for two years now, and I have nothing negative to say about them at all. They've handled every track day I've thrown at them, the durability is excellent, pedal feel very firm yet progressive, and are a huge improvement over the BMW BBK which I had on previously. It's no wonder they are used on so many race cars at the Nurburgring as the performance/cost ratio is staggeringly good value.

Front AP kit (CP5575-1009.G8) is around 1,900 + VAT and fitting .
The rear kit (CP6625-1000BK) is around 890 + VAT and fitting.
(AP Racing product codes are for Black-coloured calipers - Red calipers also available)



Bottom line - for normal road use on anything up to a 330 (pre-LCI), get the BMW BBK. For serious use, get AP Racing brakes.

And if you have a 335i or 335d, or LCI 330i or d, but don't want to go to the expense of a proper BBK, then I suggest a brake fluid upgrade to Castrol Super Response Dot 4, a pad upgrade to something by Pagid or Cool Carbon or Ferodo, and a brake line upgrade to Goodridge Stainless Steel lines
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      05-02-2009, 11:49 AM   #5
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Originally Posted by E92Fan View Post
The BMW BBK system is undeniably good value - 6pot Brembo calipers at the front, 4pot rears, drilled discs, different pads. For the money, it's unbeatable

However, you have asked a very valid question as to why they are so cheap. The thing with 6pot brakes is that across the range there is a HUGE variation in quality and performance.



Firstly, it would be an idea to understand a little bit about the design of multiple-pot calipers and the advantages/disadvantages of certain systems.


Generally, and in the most simplistic view, the most important aspects of a brake caliper design are -

a) the technical suitability of the caliper force in relation to the target vehicle
b) how evenly it distributes braking force across the entire face of the pad,
c) the heat resistant capability of that caliper in terms of the way it can dissipate heat away from the pads,
d) the long-term durability and reliability of the caliper
e) weight


There is a common misconception that the greater number of pots the better the braking system. A bigger set, or a greater number, of caliper pistons will provide more clamping pressure on that axle, but could also have a negative effect on total brake performance. If the pistons are too large for the application it will lead to excessive pedal travel and the front/rear brake balance will be adversely affected, resulting in longer stopping distances. Clamping forces can also become so strong that you'll end up locking the brakes far too early, making brake modulation and control very difficult.

In reality, the number of pots is not as important as the technical design and setup of each caliper to a particular vehicle. In the most simplistic terms, the greater the number of pistons/pots, the greater the surface area of pressure being applied to a brake pad, and hence the greater amount of friction generated (assuming the brake pad characteristics haven't changed in the comparison). However, it is more important that the correct braking force is distributed along the pad - having a more efficient 4pot system valved correctly for the vehicle will give much better braking performance than an oversized 6pot caliper with mismatched valving.

A larger brake caliper normally leads to using larger-sized pads - however, just because a pad is larger doesn't mean that there is more braking force. A bigger pad of the same compound in the same location as a smaller pad will not actually give shorter stopping distances. The stopping force or torque reaction is derived from the pad friction coefficient, the diameter of the brake disc and the amount of pressure applied. A bigger pad does not apply more pressure, only the same pressure over a bigger area. The advantage of a bigger pad lies in its heat capacity and rate of wear - the larger the pad, the more it will be able to absorb initial heat, thus suffering less thermal shock and with the consequent advantage of greater pad life.

However, there are sometimes problems with having larger pads - the popular Porsche calipers use a taller pad than most other systems, and whilst this taller pad gives slightly better heat characteristics, the system actually requires a heavier brake disc to match. This heavier disc has greater inertia and if the piston valving pressure is not adapted to suit, you actually end up with longer braking distances.

Piston/caliper design is also important - the cheaper calipers generally use stainless steel or aluminium alloy pistons coupled with simple dust boots, and are almost always of a two-piece cast aluminium design. The most expensive calipers may use titanium pistons (lighter and stronger), with much better high-temperature dust seals on each piston. They may also be of a forged monobloc design, which if designed using the correct alloys may well be stronger than a regular caliper, but may not necessarily be stiffer. A big brake kit will provide increased heat capacity, which means substantially more resistance to brake fade and caliper distortion with multiple stops from high speed. The stronger the caliper, the less the distortion and the more precise the braking performance. It will also give a firmer pedal due to stronger and stiffer components, as well as better modulation characteristics. The lighter the caliper the greater the reduction in unsprung weight, which will yield better handling and suspension characteristics on a properly setup car

Some calipers also use a differential bore design, in which smaller pistons are used up front, with larger pistons at the trailing edge of the caliper. As the surface of the brake disc heats up, the clamping force of the pistons has to be increased to maintain braking force (due to increasing fade). If the caliper has multiple pistons (or multiple pairs of pistons), the brake disc surface is initially heated by the pistons pushing against the brake pad at the leading edge of the caliper, making the disc surface hotter when it rotates back to the pistons closer to the trailing edge of the caliper. Therefore it helps if the pistons closer to the rear edge of the caliper are larger as they can deliver greater pressure.



So, with all that in mind then, why's the BMW BBK such good value?

Pros
Well, it's a basic 6 pot system (front), designed by Brembo as a two-piece aluminium caliper. It uses inexpensive standard compound Jurid/Textar brake pads (which are the regular BMW OEM pads), with basic one-piece drilled & slotted 338x26mm discs, simple individual piston dust seals and standard BMW brake hoses.

Because the caliper, and entire brake system, was designed as an OEM piece for the 135i, BMW have managed to drive the cost of that caliper down and hence can pass on the savings to the aftermarket customer. The only difference is the brake disc, which on the Performance kit is the same intrinsic disc but now drilled and slotted. The ancillaries have also been built down to a price - this is not being disrespectful to BMW, but in reality you can't imagine BMW using a 1500 brake system as standard on the 135i. For regular road use and as a standard no-thinking-required replacement for standard brakes it's a very good kit. The vast majority of BMW drivers would be very happy with this BBK as it's a fit-and-forget system And compared to the brakes on a 325i (not so much to a 335i/d) it's a vast improvement.


Cons
However, when you start exploring the higher limits of the BMW BBK there are several failings that become obvious. Firstly, it is next to impossible to get aftermarket pads for that caliper - because it's a BMW-specific caliper and not a standard Brembo shape, the likes of Pagid and Ferrodo have been very slow in developing aftermarket pads for that application. The regular BMW pads are ok for road use, but on the track they start to fade and judder very quickly. The more aggressive driver or track-day enthusiast will probably find the limits of the pad quite quickly. To be able to change to Pagid race pads for use on a track for example might be very important and necessary. Continuing this theme, it isn't easy to change the pads on the BMW BBK - the caliper has to come off. Compare that to the top-end Brembo kits where the pads are held in by quick-release pins and you can do a pad change in mere minutes.

The brake discs are one-piece items with integral bell (the bit that holds the disc onto the hub). There's no way to improve the brake disc by using aftermarket items from the likes of Performance Friction (who make arguably the world's best brake discs). The standard discs themselves also aren't as heat-resistant as they could be and will warp more easily under duress. The heat characteristics of the pistons also leave much to be desired - when out on track, under duress the pistons have a tendency to crack, whilst the seals will almost certainly disintegrate. This has been shown many times now on the 135i race cars. The caliper also displays quite uneven pressure distribution across the pistons - the last set of pads I used on my BMW BBK were noticeably warped with a 3.5mm height difference between the widest edges.

These problems only showed up when the brakes were put to more serious use. I discovered all this first hand at the Nurburgring last summer, when I subjected the brake system to only a moderately torturous test I was actually disappointed at how spectacularly the calipers failed I was reminded though that they are also spectacularly cheap and not really designed for that sort of abuse!! To BMWs credit they replaced that first kit with a new set of calipers..!

On normal road driving, the limits would not be anywhere close to being reached and so I would still recommend them as a significant performance upgrade to the standard brakes on anything up to a 330 (pre-LCI) under these conditions

I would NOT recommend the BMW BBK for someone with a 335i or 335d, or with an LCI 330i or 330d, as there are too many disadvantages going to the BBK compared with the regular OEM setup - the main problem is the discs are much smaller and thinner and can't absorb anywhere near the amount of heat that the OEM discs can




My thoughts


If you are looking to use the car on a track on more than the odd occasion, or do LOTS of high-speed driving, then I would suggest you look at a higher-spec alternative. There has been mention of the 4000/6000 Brembo GT kits etc, which are fabulous but massively over-specced for use on anything other than fully-fledged race cars.

The Tarox kits have issues of their own - the cheap kits are exactly that - cheap and nasty. The 12pot systems are ridiculously expensive, and to be honest why on earth would anyone need a 12pot system? The individual pots themselves are tiny, the weight of the caliper is huge, and the performance doesn't justify the price.

Probably the best value kit, and the one I'm now using to great effect, is the AP Racing 6pot front / 4pot rear system. The front 6pot system is a two-piece cast aluminium design using 355x32mm slotted and vented discs with separate bells, aluminium alloy pistons with individual high-temp dust seals and comes supplied with mounting brackets, braided hoses, Ferrodo DS2500 fast-road pads, and Dot 5.1 brake fluid.

The rear system uses a 4-piston version of the same caliper, Ferrodo DS2500 pads, but uses the standard rear BMW OEM discs. I believe that Stillen Racing in the USA have a different version of the rear AP system that uses replacement discs as well.

I have been using the APs for two years now, and I have nothing negative to say about them at all. They've handled every track day I've thrown at them, the durability is excellent, pedal feel very firm yet progressive, and are a huge improvement over the BMW BBK which I had on previously. It's no wonder they are used on so many race cars at the Nurburgring as the performance/cost ratio is staggeringly good value.

Front AP kit (CP5575-1009.G8) is around 1,900 + VAT and fitting .
The rear kit (CP6625-1000BK) is around 890 + VAT and fitting.
(AP Racing product codes are for Black-coloured calipers - Red calipers also available)



Bottom line - for normal road use on anything up to a 330 (pre-LCI), get the BMW BBK. For serious use, get AP Racing brakes.

And if you have a 335i or 335d, or LCI 330i or d, but don't want to go to the expense of a proper BBK, then I suggest a brake fluid upgrade to Castrol Super Response Dot 4, a pad upgrade to something by Pagid or Cool Carbon or Ferodo, and a brake line upgrade to Goodridge Stainless Steel lines

As always Tony, very informative.

I noticed a hint that the BMW BBK wasnt such a good idea on the 335i/d there - would that mean they come equipped with a better brake kit as standard?

I take it then, my best option would be the AP kit?

Matt
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      05-02-2009, 12:09 PM   #6
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As always Tony, very informative.

I noticed a hint that the BMW BBK wasnt such a good idea on the 335i/d there - would that mean they come equipped with a better brake kit as standard?

I take it then, my best option would be the AP kit?

Matt

My personal thought on the BMW BBK as a mod on a 335i/d is that whilst the braking performance is a little better, and brake fade certainly reduced under higher-duress, the advantages don't justify the 700 cost of the front kit.

IMO you can get much the same performance by changing the standard 335i/d front pads to something more performance orientated (Pagid / Ferrodo). This will cost you less than the BMW BBK. Add braided hoses and uprated fluid and you'll be pretty set.

If you want to maximise the performance of the BMW BBK then you need to change the pads, add braided hoses and change the fluid. However, fast-road pads alone will be around 180 (when they eventually become available), hoses around 60, fluid about 50 total...

If you want a proper upgrade in brakes, then I would go for the AP Racing setup...
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      05-02-2009, 06:14 PM   #7
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My personal thought on the BMW BBK as a mod on a 335i/d is that whilst the braking performance is a little better, and brake fade certainly reduced under higher-duress, the advantages don't justify the 700 cost of the front kit.

IMO you can get much the same performance by changing the standard 335i/d front pads to something more performance orientated (Pagid / Ferrodo). This will cost you less than the BMW BBK. Add braided hoses and uprated fluid and you'll be pretty set.

If you want to maximise the performance of the BMW BBK then you need to change the pads, add braided hoses and change the fluid. However, fast-road pads alone will be around 180 (when they eventually become available), hoses around 60, fluid about 50 total...

If you want a proper upgrade in brakes, then I would go for the AP Racing setup...
Well...I must say a BIG thanks for your time explaining those things (which i suppose comes from your experience).
I own a 400+ bhp 335i and I was ready to push the button for the Performance brakes. I was hesitating a bit due to the fact BMW was not proposing this upgrade for 335i but on the other hand, I heard a couple of 335 owners (who upgraded to the BMW Performance kit) to be extremely satisfied from the performance. To be honnest I was disspointed a bit from your above "review" as the BMW Performance was a very affordable upgrade...but doesnt look the right decision for me now.

The AP is a very prestigious brand ...can you give me some info on the brake kit you are talking about?
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      05-03-2009, 04:35 AM   #8
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Thank you E92Fan for that very informative piece of automotive literature! I've copied and pasted your post onto my computer so I can refer to it whenever I'm a bit confused

I must say the AP Racing kits do look like a real alternative to the BMW BBK after you highlighted the pros and cons. It helped greatly.
I'm quite surprised with the price as well, being leaps and bounds cheaper than the rivals even with their racing background.

I feel I might be giving Birds a call this week to get a quote for a 325i.
I have visited the Ring only once yet, and managed to do 4 laps during my stay using the OEM brakes. As expected, they did fade considerably after each lap but according to BMW do not need to be changed yet.

Now either I was not driving as hard as I could have, or it is true what some journalists say about the Ring when compared to smaller F1 style circuits; that with its longs fast sections and corners, the Ring actually goes easier on a car's brakes. Which is why I feel the BMW BBK might suffice for the type of driving I do.

However, I do not want to come across the time when I begin visiting track days in the UK and Europe and begin to see my nice Green/Gold brakes degrade in a matter of laps.
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      05-04-2009, 05:16 AM   #9
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Quote:
Originally Posted by -=TSL=- View Post
Thank you E92Fan for that very informative piece of automotive literature! I've copied and pasted your post onto my computer so I can refer to it whenever I'm a bit confused

I must say the AP Racing kits do look like a real alternative to the BMW BBK after you highlighted the pros and cons. It helped greatly.
I'm quite surprised with the price as well, being leaps and bounds cheaper than the rivals even with their racing background.

I feel I might be giving Birds a call this week to get a quote for a 325i.
I have visited the Ring only once yet, and managed to do 4 laps during my stay using the OEM brakes. As expected, they did fade considerably after each lap but according to BMW do not need to be changed yet.

Now either I was not driving as hard as I could have, or it is true what some journalists say about the Ring when compared to smaller F1 style circuits; that with its longs fast sections and corners, the Ring actually goes easier on a car's brakes. Which is why I feel the BMW BBK might suffice for the type of driving I do.

However, I do not want to come across the time when I begin visiting track days in the UK and Europe and begin to see my nice Green/Gold brakes degrade in a matter of laps.
I have a feeling that the BMW BBK might suffice for you - on a 325i the difference between the standard brakes and the BMW BBK will be quite large, and if you found the standard brakes ok, then you'll be more than pleased with the BMW BBK upgrade.

If however you are going to be doing a lot more trackdays and 'Ring trips, you might be able to justify the AP Racing setup as you'll then have a choice of pads to select, and can swap between road and track setups very easily. Also, don't think that you'll need the rear upgrade as well - just having the front 6pot brakes will be ok and doesn't upset the handling of the car noticeably. Even under very hard braking there's no tendency for the rear end to start weaving. The rear upgrade is just the icing on the cake, and brings the front/rear brake bias back to the final degree of neutrality.
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      05-04-2009, 05:19 AM   #10
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Great 1st hand info E92Fan But are you on kick-backs from Birds?
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      05-04-2009, 05:24 AM   #11
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Great 1st hand info E92Fan But are you on kick-backs from Birds?
I wish Bit late now - they've already done all the work on my car

Actually, in all seriousness I recommend Birds because I know they'll do an excellent job. I don't ever want a situation where I recommend someone, a forum member goes there on the back of my recommendation, and their car gets screwed up or damaged etc...!

ps... and in this situation they're also APs most trusted supplier/installer in and around London!!
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      05-04-2009, 05:58 AM   #12
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Tony, as ever an excellent and informative response, I understand far more about brakes just from reading this than I ever have


As you know I have the BMW kit all round now complimented by braided hoses etc and still running on the standard pads.

My 335 has done a mere 4 laps of the ring and the recent Bedford AM session on this set up, in between it is mainly used by my wife for buisiness use so is treated gently, she keeps complaining about an intermittent squeak from the rear n/side wheel, definetly rotational.

Any thoughts ? I'm even considering putting the standard brakesback on the rear just to get a 'quiet' life
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      05-04-2009, 06:04 PM   #13
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Tony, as ever an excellent and informative response, I understand far more about brakes just from reading this than I ever have


As you know I have the BMW kit all round now complimented by braided hoses etc and still running on the standard pads.

My 335 has done a mere 4 laps of the ring and the recent Bedford AM session on this set up, in between it is mainly used by my wife for buisiness use so is treated gently, she keeps complaining about an intermittent squeak from the rear n/side wheel, definetly rotational.

Any thoughts ? I'm even considering putting the standard brakesback on the rear just to get a 'quiet' life

The rear BBK shouldn't be giving you any squeaks - the pads are regular Jurid/Textar pads so there isn't a high enough carbon content to give any constant squeaking. Also, the calipers run quite a lot of clearance around the disc, so it's unlikely it's pad squeal (unless the caliper is sticking slightly). Could be the rear pad sensor is rubbing occasionally. Or there's a bit of grit stuck in the caliper that's scoring the disc. Is the squeak on braking only, or during unbraked motion as well? Worst case scenario is that the hub bearing is a little worn. Best get it looked at (under warranty) by your local dealer...
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      05-05-2009, 02:51 AM   #14
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The squeaking is in 'un-braked' motion only and intermittent which adds to the frustration, Speed religion and my local BMW delaer have both taken a look but on each visit the car decided to remain silent, Grrrrrr

Local dealer claims its 'normal' with BMW performance pads, yeah right, never happened once on the 1 series?!

Ant at Speed religion thinks the disc may have developed a slight un-used edge that may or may not be the cause, loacl dealer won't look any further unles I pay for the investigation as brakes not approved for 335 use, how helpful

Pretty sure its not grit as this usually clears, the squeaking can be eradicated by some overly heavy braking but this is not ideal on busy roads
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      05-06-2009, 05:03 PM   #15
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E92Fan,
if fitting the BMW performance brakes front and rear, i understand the ABS (part of the DSC) needs to be reset by BMW. Is this also true for the AP kit?
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      05-06-2009, 05:12 PM   #16
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BMW do say that the ABS/DSC systems need to be 'reset'... quite what that entails no one is quite sure, except that it has become apparent that it is totally unnecessary!!!

Ant from SpeedReligion has now installed lots of the BMW BBK kits on 335i/ds, which don't allow the ABS/DSC parameters to be changed as the BBK is not an official authorised retrofit kit. There has never been an issue with any car, not with brake balance, excessive pad wear, or ABS sensor failure etc...

The same goes for my car with APs all round, the Birds demo car, and the tens of other Birds customers who have APs - none of the parameters have ever been changed, and yet braking performance has been nothing short of exemplary under all manner of driving conditions.

Bottom line - I wouldn't worry about it!
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      05-07-2009, 10:58 AM   #17
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Thumbs up Great post!

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Originally Posted by E92Fan View Post
The BMW BBK system is undeniably good value - 6pot Brembo calipers at the front, 4pot rears, drilled discs, different pads. For the money, it's unbeatable

However, you have asked a very valid question as to why they are so cheap. The thing with 6pot brakes is that across the range there is a HUGE variation in quality and performance.



Firstly, it would be an idea to understand a little bit about the design of multiple-pot calipers and the advantages/disadvantages of certain systems.


Generally, and in the most simplistic view, the most important aspects of a brake caliper design are -

a) the technical suitability of the caliper force in relation to the target vehicle
b) how evenly it distributes braking force across the entire face of the pad,
c) the heat resistant capability of that caliper in terms of the way it can dissipate heat away from the pads,
d) the long-term durability and reliability of the caliper
e) weight


There is a common misconception that the greater number of pots the better the braking system. A bigger set, or a greater number, of caliper pistons will provide more clamping pressure on that axle, but could also have a negative effect on total brake performance. If the pistons are too large for the application it will lead to excessive pedal travel and the front/rear brake balance will be adversely affected, resulting in longer stopping distances. Clamping forces can also become so strong that you'll end up locking the brakes far too early, making brake modulation and control very difficult.

In reality, the number of pots is not as important as the technical design and setup of each caliper to a particular vehicle. In the most simplistic terms, the greater the number of pistons/pots, the greater the surface area of pressure being applied to a brake pad, and hence the greater amount of friction generated (assuming the brake pad characteristics haven't changed in the comparison). However, it is more important that the correct braking force is distributed along the pad - having a more efficient 4pot system valved correctly for the vehicle will give much better braking performance than an oversized 6pot caliper with mismatched valving.

A larger brake caliper normally leads to using larger-sized pads - however, just because a pad is larger doesn't mean that there is more braking force. A bigger pad of the same compound in the same location as a smaller pad will not actually give shorter stopping distances. The stopping force or torque reaction is derived from the pad friction coefficient, the diameter of the brake disc and the amount of pressure applied. A bigger pad does not apply more pressure, only the same pressure over a bigger area. The advantage of a bigger pad lies in its heat capacity and rate of wear - the larger the pad, the more it will be able to absorb initial heat, thus suffering less thermal shock and with the consequent advantage of greater pad life.

However, there are sometimes problems with having larger pads - the popular Porsche calipers use a taller pad than most other systems, and whilst this taller pad gives slightly better heat characteristics, the system actually requires a heavier brake disc to match. This heavier disc has greater inertia and if the piston valving pressure is not adapted to suit, you actually end up with longer braking distances.

Piston/caliper design is also important - the cheaper calipers generally use stainless steel or aluminium alloy pistons coupled with simple dust boots, and are almost always of a two-piece cast aluminium design. The most expensive calipers may use titanium pistons (lighter and stronger), with much better high-temperature dust seals on each piston. They may also be of a forged monobloc design, which if designed using the correct alloys may well be stronger than a regular caliper, but may not necessarily be stiffer. A big brake kit will provide increased heat capacity, which means substantially more resistance to brake fade and caliper distortion with multiple stops from high speed. The stronger the caliper, the less the distortion and the more precise the braking performance. It will also give a firmer pedal due to stronger and stiffer components, as well as better modulation characteristics. The lighter the caliper the greater the reduction in unsprung weight, which will yield better handling and suspension characteristics on a properly setup car

Some calipers also use a differential bore design, in which smaller pistons are used up front, with larger pistons at the trailing edge of the caliper. As the surface of the brake disc heats up, the clamping force of the pistons has to be increased to maintain braking force (due to increasing fade). If the caliper has multiple pistons (or multiple pairs of pistons), the brake disc surface is initially heated by the pistons pushing against the brake pad at the leading edge of the caliper, making the disc surface hotter when it rotates back to the pistons closer to the trailing edge of the caliper. Therefore it helps if the pistons closer to the rear edge of the caliper are larger as they can deliver greater pressure.



So, with all that in mind then, why's the BMW BBK such good value?

Pros
Well, it's a basic 6 pot system (front), designed by Brembo as a two-piece aluminium caliper. It uses inexpensive standard compound Jurid/Textar brake pads (which are the regular BMW OEM pads), with basic one-piece drilled & slotted 338x26mm discs, simple individual piston dust seals and standard BMW brake hoses.

Because the caliper, and entire brake system, was designed as an OEM piece for the 135i, BMW have managed to drive the cost of that caliper down and hence can pass on the savings to the aftermarket customer. The only difference is the brake disc, which on the Performance kit is the same intrinsic disc but now drilled and slotted. The ancillaries have also been built down to a price - this is not being disrespectful to BMW, but in reality you can't imagine BMW using a 1500 brake system as standard on the 135i. For regular road use and as a standard no-thinking-required replacement for standard brakes it's a very good kit. The vast majority of BMW drivers would be very happy with this BBK as it's a fit-and-forget system And compared to the brakes on a 325i (not so much to a 335i/d) it's a vast improvement.


Cons
However, when you start exploring the higher limits of the BMW BBK there are several failings that become obvious. Firstly, it is next to impossible to get aftermarket pads for that caliper - because it's a BMW-specific caliper and not a standard Brembo shape, the likes of Pagid and Ferrodo have been very slow in developing aftermarket pads for that application. The regular BMW pads are ok for road use, but on the track they start to fade and judder very quickly. The more aggressive driver or track-day enthusiast will probably find the limits of the pad quite quickly. To be able to change to Pagid race pads for use on a track for example might be very important and necessary. Continuing this theme, it isn't easy to change the pads on the BMW BBK - the caliper has to come off. Compare that to the top-end Brembo kits where the pads are held in by quick-release pins and you can do a pad change in mere minutes.

The brake discs are one-piece items with integral bell (the bit that holds the disc onto the hub). There's no way to improve the brake disc by using aftermarket items from the likes of Performance Friction (who make arguably the world's best brake discs). The standard discs themselves also aren't as heat-resistant as they could be and will warp more easily under duress. The heat characteristics of the pistons also leave much to be desired - when out on track, under duress the pistons have a tendency to crack, whilst the seals will almost certainly disintegrate. This has been shown many times now on the 135i race cars. The caliper also displays quite uneven pressure distribution across the pistons - the last set of pads I used on my BMW BBK were noticeably warped with a 3.5mm height difference between the widest edges.

These problems only showed up when the brakes were put to more serious use. I discovered all this first hand at the Nurburgring last summer, when I subjected the brake system to only a moderately torturous test I was actually disappointed at how spectacularly the calipers failed I was reminded though that they are also spectacularly cheap and not really designed for that sort of abuse!! To BMWs credit they replaced that first kit with a new set of calipers..!

On normal road driving, the limits would not be anywhere close to being reached and so I would still recommend them as a significant performance upgrade to the standard brakes on anything up to a 330 (pre-LCI) under these conditions

I would NOT recommend the BMW BBK for someone with a 335i or 335d, or with an LCI 330i or 330d, as there are too many disadvantages going to the BBK compared with the regular OEM setup - the main problem is the discs are much smaller and thinner and can't absorb anywhere near the amount of heat that the OEM discs can




My thoughts


If you are looking to use the car on a track on more than the odd occasion, or do LOTS of high-speed driving, then I would suggest you look at a higher-spec alternative. There has been mention of the 4000/6000 Brembo GT kits etc, which are fabulous but massively over-specced for use on anything other than fully-fledged race cars.

The Tarox kits have issues of their own - the cheap kits are exactly that - cheap and nasty. The 12pot systems are ridiculously expensive, and to be honest why on earth would anyone need a 12pot system? The individual pots themselves are tiny, the weight of the caliper is huge, and the performance doesn't justify the price.

Probably the best value kit, and the one I'm now using to great effect, is the AP Racing 6pot front / 4pot rear system. The front 6pot system is a two-piece cast aluminium design using 355x32mm slotted and vented discs with separate bells, aluminium alloy pistons with individual high-temp dust seals and comes supplied with mounting brackets, braided hoses, Ferrodo DS2500 fast-road pads, and Dot 5.1 brake fluid.

The rear system uses a 4-piston version of the same caliper, Ferrodo DS2500 pads, but uses the standard rear BMW OEM discs. I believe that Stillen Racing in the USA have a different version of the rear AP system that uses replacement discs as well.

I have been using the APs for two years now, and I have nothing negative to say about them at all. They've handled every track day I've thrown at them, the durability is excellent, pedal feel very firm yet progressive, and are a huge improvement over the BMW BBK which I had on previously. It's no wonder they are used on so many race cars at the Nurburgring as the performance/cost ratio is staggeringly good value.

Front AP kit (CP5575-1009.G8) is around 1,900 + VAT and fitting .
The rear kit (CP6625-1000BK) is around 890 + VAT and fitting.
(AP Racing product codes are for Black-coloured calipers - Red calipers also available)



Bottom line - for normal road use on anything up to a 330 (pre-LCI), get the BMW BBK. For serious use, get AP Racing brakes.

And if you have a 335i or 335d, or LCI 330i or d, but don't want to go to the expense of a proper BBK, then I suggest a brake fluid upgrade to Castrol Super Response Dot 4, a pad upgrade to something by Pagid or Cool Carbon or Ferodo, and a brake line upgrade to Goodridge Stainless Steel lines
This is one of the most logical and thorough posts I have come across in a variety of forums that I peruse regularly. It is not only insightful, but actually help in terms of leading a person to a decision based on their situation, not only on what fits a particular car.

If I could only clarify one issue that is oft repeated, but not necessarily in line with engineering principles. A forged monoblock caliper is not necessarily stiffer than a well-made 2-piece design. Forged aluminum has virtually the same Modulus of Elasticity as that of cast aluminum. The forged piece will likely (if the correct choices are made with alloys, tooling and thermal post-treatments) be stronger, but not stiffer. Notice that I am not including poorly made cast calipers into this discussion. Those are garbage and should not be run on any vehicle at any time.

Forging is great for things like pistons and connecting rods, but is doesn't help calipers a whole lot. Since calipers are a stiffness-based design (more stiff = better control, feel and pad support), they are always stronger than they need to be. The failure mode of pistons is breakage -- for calipers it is excessive flex, so it is stiffness vs. weight that we are after. Forging does not buy much of anything in that pursuit, other than higher cost. In fact, a well-designed and produced 2-piece caliper is often stiffer than an average monoblock. The steel bridge bolts, if properly designed and installed, are steel, so they add stiffness in all four flex modes (spreading, bowing, twist and clamshell). The notable exception would be when very expensive materials were allowed in Formula 1 years ago. THOSE monoblocks were approaching the stiffness of steel and used a material only slightly more dense than aluminum. However, there is no way these materials can be used on brake systems that need to cost less than US$15-20k.

Again, this is an outstanding post. Anyone seriously considering brake upgrades would be well served by reading it at least a few times.

Chris
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      05-07-2009, 11:44 AM   #18
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Quote:
Originally Posted by AP Racing - Chris_B View Post
This is one of the most logical and thorough posts I have come across in a variety of forums that I peruse regularly. It is not only insightful, but actually help in terms of leading a person to a decision based on their situation, not only on what fits a particular car.

If I could only clarify one issue that is oft repeated, but not necessarily in line with engineering principles. A forged monoblock caliper is not necessarily stiffer than a well-made 2-piece design. Forged aluminum has virtually the same Modulus of Elasticity as that of cast aluminum. The forged piece will likely (if the correct choices are made with alloys, tooling and thermal post-treatments) be stronger, but not stiffer. Notice that I am not including poorly made cast calipers into this discussion. Those are garbage and should not be run on any vehicle at any time.

Forging is great for things like pistons and connecting rods, but is doesn't help calipers a whole lot. Since calipers are a stiffness-based design (more stiff = better control, feel and pad support), they are always stronger than they need to be. The failure mode of pistons is breakage -- for calipers it is excessive flex, so it is stiffness vs. weight that we are after. Forging does not buy much of anything in that pursuit, other than higher cost. In fact, a well-designed and produced 2-piece caliper is often stiffer than an average monoblock. The steel bridge bolts, if properly designed and installed, are steel, so they add stiffness in all four flex modes (spreading, bowing, twist and clamshell). The notable exception would be when very expensive materials were allowed in Formula 1 years ago. THOSE monoblocks were approaching the stiffness of steel and used a material only slightly more dense than aluminum. However, there is no way these materials can be used on brake systems that need to cost less than US$15-20k.

Again, this is an outstanding post. Anyone seriously considering brake upgrades would be well served by reading it at least a few times.

Chris


Thanks for adding the information regarding forged calipers I wasn't aware that forged aluminium had more or less the same elasticity properties of cast aluminium - I was always under the impression that, when processed properly and correctly, that forging created a more robust product than the equivalent casting.

Given you work for AP, or at the very least work with AP products, is there any chance of them making a proper vented two-piece 336x22mm disc for the rear of the 335i kit ?? Really annoying that I'm using the standard BMW disc (even though I know there's very little real-world performance advantage in upgrading the rear discs!)
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      05-07-2009, 12:23 PM   #19
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Thanks for adding the information regarding forged calipers I wasn't aware that forged aluminium had more or less the same elasticity properties of cast aluminium - I was always under the impression that, when processed properly and correctly, that forging created a more robust product than the equivalent casting.

Given you work for AP, or at the very least work with AP products, is there any chance of them making a proper vented two-piece 336x22mm disc for the rear of the 335i kit ?? Really annoying that I'm using the standard BMW disc (even though I know there's very little real-world performance advantage in upgrading the rear discs!)
Forging does have its advantage for a variety of parts. Brake calipers are helped much less by this process than some others.

There is a 335i system available here in the USA, manufactured in partnership between AP Racing and Stillen. There are forum supporting vendors that sell these kits that I am sure will be happy to quote you. Ask for AP6400 (front 6-piston 362x32mm 2-piece disc -- add an 'S' to the part number if you wanted slotted discs) and AP6450 (rear 4-piston 330x25.4mm 2-piece disc - same suffix for slotted). Both front and rear discs are curved-vane vented. I'm not sure who in the UK is the best to contact, so you might need to talk to someone on this side of the pond.

Of course, it looks like you already have a front system installed, so the rear system above would actually be a nice compliment. It shifts the balance very slightly rearward to offset the slight front shift that your car is currently experiencing. Balance, as it always has been, is the key.
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      05-07-2009, 12:43 PM   #20
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Forging does have its advantage for a variety of parts. Brake calipers are helped much less by this process than some others.

There is a 335i system available here in the USA, manufactured in partnership between AP Racing and Stillen. There are forum supporting vendors that sell these kits that I am sure will be happy to quote you. Ask for AP6400 (front 6-piston 362x32mm 2-piece disc -- add an 'S' to the part number if you wanted slotted discs) and AP6450 (rear 4-piston 330x25.4mm 2-piece disc - same suffix for slotted). Both front and rear discs are curved-vane vented. I'm not sure who in the UK is the best to contact, so you might need to talk to someone on this side of the pond.

Of course, it looks like you already have a front system installed, so the rear system above would actually be a nice compliment. It shifts the balance very slightly rearward to offset the slight front shift that your car is currently experiencing. Balance, as it always has been, is the key.

I already have the rear 4pot kit using a 6625 caliper and custom bracketing that allows the use of standard BMW rear disc. I need to work out how to change the disc, if there is a direct replacement, or if I can change the rear brackets to accommodate a slightly different dimensioned disc. AP UK don't have a suitable replacement, PFC haven't made one either (and if I do want them to make a special product, I need to order 50 pieces...)

And yes you're quite right in saying that the rear kit rebalances the brake bias to more neutrality. Whilst having the front kit alone wasn't a problem for me, under extreme braking out on track the rear balance was a little light... the AP rear kit has resolved that very slight issue for me...
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      05-07-2009, 02:18 PM   #21
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This reminds me of the time when Georgie LaForge had a conversation with Cmdr Data about Interstellar Displacement.

I like it, in fact, I find it enthralling, but I am largely unaware of whats going on.

Brilliant

Matt
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      05-07-2009, 02:21 PM   #22
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Quote:
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I already have the rear 4pot kit using a 6625 caliper and custom bracketing that allows the use of standard BMW rear disc. I need to work out how to change the disc, if there is a direct replacement, or if I can change the rear brackets to accommodate a slightly different dimensioned disc. AP UK don't have a suitable replacement, PFC haven't made one either (and if I do want them to make a special product, I need to order 50 pieces...)

And yes you're quite right in saying that the rear kit rebalances the brake bias to more neutrality. Whilst having the front kit alone wasn't a problem for me, under extreme braking out on track the rear balance was a little light... the AP rear kit has resolved that very slight issue for me...
I'm not sure there is enough room to actually accomplish what you are looking for with the OE rotor dimensions. The ID of the fire path is very close the hat/bell OD, which means it is difficult to create a land area for the fasteners. The larger annulus disc was one way around this challenge.

The AP6450 kit uses the CP5147 caliper and a slightly thicker disc. Unfortunately, the mounting dimensions are different between those two calipers so a bracket that fits one is useless for the other. Add to that the fact that the CP6625 could not take the thicker disc.

This is one of those situations when many in the market were calling for lower prices. AP Racing answered that call by using the OE rear disc (using the front OE disc was deemed unacceptable for a serious upgrade). Of course, there are also some calling for a 2-piece solution, which is what Stillen did. Sadly, they are just not interchangeable as far as parts go.
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