Differences Between Brembo 380mm/380mm BBK and 365mm/345mm BBK

[sparkyg]

I am considering getting the smaller of the BBK since I need to use 18's for winter driving.

Yes I know a BBK is not the first on the list of mods I should do but I already have done all those mods.

My main goals are the best brakes for the dollar and to improve what I already have. I may do some track and autocross but it will be just weekend type events.

My questions are

1) Does the kit use the same disc design for the larger and smaller kit? Are they the same material, same specs, just smaller?

2) Are the pads the same?

3) Are the calipers the same for the two kits? They say they are both 6 pot front and 4 pot rear, but are they identical mono calipers?

4) How is the proper brake balance achieved for the 380/380 kit vs the 365/345 kit? Do you change orifices in the brake lines? What changes?

5) Are the accessories with each kit the same, same lines, same brackets or are they different only in dimensions but not materials and relative strength

Thx for any info.

As I said it is only a consideration right now but I need to be better informed of what one gets for the money.

Does anyone else know of BBK that you can use the stock 18's with?

[STALKER]

I believe just the disc sizes are diff, rest is the same.
These are suppose to clear OEM 18s without spacers.
Stoptech has a smaller kit now too, I thin they use a 355/355 combo. I believe that the Performance Friction it will clear OEM 18s aswell, but their discs are a little larger and are 4 pot calipers. PF stuff is high end.

Personally when the time comes, I will be going with the 365/345 kit.

[Gary_C]

Lot's of good questions, let's just get straight to it...

Originally Posted by sparkyg

1) Does the kit use the same disc design for the larger and smaller kit? Are they the same material, same specs, just smaller?

Every Gran Turismo brake kit follows the same philosophy for vehcile specific engineering, providing optimum brake bias, based on the factory master cylinder, ABS, and other traction control devices.

The calipers for both systems are a 6-piston monobloc.
The discs for both systems come directly from the racing division.

The only differences are in the details of each component selected to appropriately match the application.

Originally Posted by sparkyg

2) Are the pads the same?

The replacement pads will be the same between wither system.

Originally Posted by sparkyg

3) Are the calipers the same for the two kits? They say they are both 6 pot front and 4 pot rear, but are they identical mono calipers?

The calipers are indeed 6-piston monobloc front and 4-piston monobloc rear for either system.
The will though, utilize different piston diameters to provide proper bias for the M3 application.

A properly developed brake system is essentially a mathematical equation.
Any changes to one component, requires a change to another, in order to achieve the same end result.

Originally Posted by sparkyg

4) How is the proper brake balance achieved for the 380/380 kit vs the 365/345 kit? Do you change orifices in the brake lines? What changes?

The changes are in both the disc diameters as well as the piston diameters.

Brake torque is a factor of line pressure (dictated by the vehicle), effective radius (dictated by the disc diameter), and piston area (dictated by the piston sizes within the caliper). Since we do not make any changes or modifications to the vehicle itself that leaves us in control of the disc sizing and caliper selection. As i stated before, changes to one of these factors dictates changes to another.

The typical rule of thumb is that if you increase the disc diameter (increasing the effective radius), you will need to correct the piston area (usually decreasing the piston sizing).

No changes are made to the brake lines or any other components that may affect line pressure. And all of the changes that are made are done so in a way that they still provide a firm but controllable brake pedal, and do not affect the function of ABS or other traction control devices.

Originally Posted by sparkyg

5) Are the accessories with each kit the same, same lines, same brackets or are they different only in dimensions but not materials and relative strength

Yes, everything else stays the same. Safety is a large part of Brembo's criteria for design. Each component is redesigned around each significant change and all of the same testing procedures and approval process are followed.

Each system was designed independently of each other and nothing is shared except for a the brake line. The key issue with the design of the systems for the M3 was heat capacity. The OEM disc is already very large in terms of mass and maximum heat capacity. Other offerings in the 355mm range may actually be offering less than ideal heat capacity for track or track like driving styles. You do need to beware of that type of approach from other manufacturers. As much as we'd like to make the smallest kit possible to fit under any/every wheel possible, there is a point where you are effectively creating the exact opposite of an "upgrade".

[sparkyg]

Thx Gary.

Now the million dollar question, slotted vs drilled.

My understanding of both is that it helps clear the brake dust from the rotor.

1) Rumors are that the drilled can tend to crack for reasons such as too high cooling rate (?) Is this true, was it ever true?

2) Drilled brakes appear to be lighter since more material is removed. Is this true? Is the drillling only on the face as it appears to be? Or do the slotted and drilled weigh the same?

3) Can one vendors brakes outperform another when they have the exact same size rotor? Is this a case of caliper design, pad material, number of pistons and piston area?

For my application, I intend to do 80% street and 20% event based (track, autocross, etc) What would be recommended irrelevent of vendors.

It appears that all the BBK on the forums are drilled? Are drilled really better for street use or is appearance playing a large role?

[2thdr]

Welcome to the dark side...lol.

[sparkyg]

Originally Posted by 2thdr

Welcome to the dark side...lol.

Yes, I am so weak and the braking force is so strong

[Gary_C]

The simplest way to break it down is by application and usage.

Primarily street - Drilled
Any significant track usage - Slotted

Originally Posted by sparkyg

1) Rumors are that the drilled can tend to crack for reasons such as too high cooling rate (?) Is this true, was it ever true?

The rumors of drilled rotors cracking come from soo many different sources and schools of thought that it's hard to even know where to begin.

The truth of the matter is that a properly drilled disc, when used with the proper pad compound for the intended use, will last just as long as a smooth or slotted surface disc. In very high temp scenarios a drilled rotor will suffer from more extreme heat cycles which does cause it to wear faster. This is why it's not generally recommended for use with race pads, or extended track sessions.

All discs suffer from the same type of wear with extreme spikes in temperatures, the reason that drilled discs have been known to suffer the most is that the common cracking seen in ALL discs near the end of their life span tend to start at the holes and grow from that point. Rather than acknowledging the root of the problem people simply blamed the hole itself.

2) Drilled brakes appear to be lighter since more material is removed. Is this true? Is the drillling only on the face as it appears to be? Or do the slotted and drilled weigh the same?

Drilled discs are in fact lighter. In a 14" disc is can be almost 1/2 lb.
The discs are drilled on both the inboard and outboard side of the disc.
Each Brembo discs has a specifically engineered drill pattern specific to the discs dimensions and vein structure. Brembo discs have less problems with premature cracking and wear than any other brand.

3) Can one vendors brakes outperform another when they have the exact same size rotor? Is this a case of caliper design, pad material, number of pistons and piston area?

Absolutely. You can only "fake it" for so long and the quality of the product will eventually show through. There are many other brands that offer the same size disc, caliper with the same # of pistons, and make all the same claims as to the benefits of their brake system. It has been proven time and time again that Brembo's build quality is second to none and that is what makes it a better value over the lifetime of the system. You can easily save a few hundred to even a thousand dollars with another brand. But once you start replacing parts, and utilizing their customer service department to help work through problems, you ultimately spend more time and more money trying to achieve what the system should have provided to begin with.

It appears that all the BBK on the forums are drilled? Are drilled really better for street use or is appearance playing a large role?

It really depends on what forums you are looking on. Of all the Brembo kits sold, I would estimate that 60% are primarily street cars with very few that do see real track time, and 40% are consistently at HPDE, Autocross and Club race events.. Of that 60% a good majority are more luxury car or SUV's. This figure is based on the # of kits that leave our doors with slotted vs. drilled discs, and the amount of feedback we get regularly from our dealers who are supporting the consumers who are actively tracking their vehicles.

[TTBear]

Great info, here. Thanks, all.
Hope this isn't too much of a thread jack, and apologies to the OP if this is so, but can anyone tell me if the 380mm BBK will fit behind OEM 18" wheels with spacers? I tried searching, but found nada.

Cheers

[sparkyg]

No, it will not fit at all.

The 365 mm kit is tight and may need spacers but the 380 mm kit needs 19" wheels minimum.

I ordered the 365/345 kit and hope to use my stock 18's.

Will keep everyone in the loop. I have a set of 19's for summer so no problem there.

[TTBear]

Thanks, Sparky. Would really appreciate your continued feedback regarding this!

Cheers!

[bigjae1976]

Subscribed...

[lucid]

Originally Posted by sparkyg

No, it will not fit at all.

The 365 mm kit is tight and may need spacers but the 380 mm kit needs 19" wheels minimum.

I ordered the 365/345 kit and hope to use my stock 18's.

Will keep everyone in the loop. I have a set of 19's for summer so no problem there.

Can you please weigh the rotors and the calipers (with pads) separately and post numbers? Thanks.

[sparkyg]

Originally Posted by lucid

Can you please weigh the rotors and the calipers (with pads) separately and post numbers? Thanks.

Yeah no problem.

I went with slotted so we'll have a good mix of numbers for those looking to purchase.

I'll have them a couple weeks.

[lucid]

Originally Posted by sparkyg

Yeah no problem.

I went with slotted so we'll have a good mix of numbers for those looking to purchase.

I'll have them a couple weeks.

I am particularly interested in seeing how much of an increase in thermal mass these result in compared to the stock rotors. I assume the calipers will weigh less than stock though.

[SenorFunkyPants]

With most BBKs the rotors generally weigh about the same as stock, the hats and calipers are lighter and allows for the claims in weight savings. The total thermal capacity of the whole BBK system will generally be less than OEM but the rate at which a larger diameter rotor (primary heat sink) can dissipate heat should be a little higher.

[lucid]

Originally Posted by SenorFunkyPants

With most BBKs the rotors generally weigh about the same as stock, the hats and calipers are lighter and allows for the claims in weight savings. The total thermal capacity of the whole BBK system will generally be less than OEM but the rate at which a larger diameter rotor (primary heat sink) can dissipate heat should be a little higher.

Heat transfer out of the rotor via convection in negligible while braking (I made some rough estimates which were in the order of 2% or less of the heat that was being transferred into the rotor). When you are not braking, the larger diameter would translate to slightly higher surface area for convection, but there the real factor is the convective heat transfer coefficient, which has to due with airflow characteristics, which has a lot to do with the vent geometry, cool air supply, etc.

Also, it seems like the stock hats are also Al, so I don't see how aftermarket hats can be significantly lighter than stock.

[SenorFunkyPants]

Originally Posted by lucid

Heat transfer out of the rotor via convection in negligible while braking (I made some rough estimates which were in the order of 2% or less of the heat that was being transferred into the rotor). When you are not braking, the larger diameter would translate to slightly higher surface area for convection, but there the real factor is the convective heat transfer coefficient, which has to due with airflow characteristics, which has a lot to do with the vent geometry, cool air supply, etc.

Does Brembo rotors have significantly better designed cooling than OEM?
It always struck me that developing better cooling ducting to the OEM brakes (with uprated pads/fluid) would be a far better cost/benefit upgrade than fitting larger brake hardware.

Originally Posted by lucid

Also, it seems like the stock hats are also Al, so I don't see how aftermarket hats can be significantly lighter than stock.

Its something that Brembo boast so I take them at their word. Some BBKs do seem to have adopted a larger diameter hat than OEM to help offset the weight that a larger diameter rotor imposes.

[sparkyg]

Lighter than stock, see thread for lots of good info

And this was the 380 mm kit so the 365 mm drilled rotor will be lighter yet

http://www.m3post.com/forums/showthr...=140719&page=3

[SenorFunkyPants]

Originally Posted by sparkyg

Lighter than stock, see thread for lots of good info

And this was the 380 mm kit so the 365 mm drilled rotor will be lighter yet

http://www.m3post.com/forums/showthr...=140719&page=3

If I'm understanding correctly, ~7% lighter rotors = ~7% less thermal capacity which would need significantly improved cooling to balance it back to OEM?

[STALKER]

The cooling vanes on a Brembo rotor are very diff then the OEM stuff.
My e46 M3 had a complete Brembo BBK, was tracked regularly and I never had a hint of brake fade.

[sparkyg]

Yeah, I would expect the Brembo to pump air thorugh that like like a piston.

Will still be interesting on how it performs

[lucid]

Originally Posted by sparkyg

Lighter than stock, see thread for lots of good info

And this was the 380 mm kit so the 365 mm drilled rotor will be lighter yet

http://www.m3post.com/forums/showthr...=140719&page=3

OC's stock rotor numbers were revised with a scale that seems more accurate by Badfish here:

http://www.m3post.com/forums/showthread.php?t=170932

So, I am not sure that those Brembo numbers were accurate either.