[obLu]

I'm wondering what you guys think would be more beneficial to performance? A BBK or just aftermarket pads on an aftermarket rotor using the oem caliper?

I've always kind of been dubious about BBKs ... I guess I just don't understand how you're physically getting more stopping power out of a bigger caliper without also putting in a bigger master cylinder to give it more clamping power? I'm also dubious when they say, "our bbk has the correct brake bias". That would tell me the BBK isn't actually applying anymore clamping power. I mean, say oem is 72% front 28% rear. To keep the same bias, the BBK front would still only be doing 72% front right?

So does the increased performance really come from the caliper or is it coming from the aftermarket friction material?

They sure do look cool ... and I'm planning my next toy so I'm intrigued.

[Rob * UUC Motorwerks]

These are excellent questions, and really show how the marketing of some BBKs can be confusing.

First, let's get this out of the way: do not expect a BBK to give you shorter stopping distances. That is not the purpose at all.

The benefits of a big brake kit include much greater heat absorption and dissipation capability due to larger heat sink areas of pad and rotor, better repeatability of performance and resistance to fade due to this greater heat capacity (known as heat management), better pedal feel and modulation, and more durable component life. With some systems, you're even reducing weight... even with larger rotors, the aluminum rotor hat and aluminum caliper weigh substantially less than the cast iron original components.

Tires play a bigger role in your actual stopping distances, a stickier tire will allow more energy transformation (changing kinetic energy into heat energy at the friction point of tire meeting road), so if you ditch the all-seasons and strap on some performance tires, your braking distance will go down.

But in an enthusiast-driven car, braking distance is only one factor, and not the most important one. As above, repeatability is important... this means that in performance driving, particularly like an organized HPDE, the margin with a BBK before brake fade or failure is much greater. Your brakes will be able to convert and dissipate more energy (again kinetic into heat) quickly and with more reserve capacity than the smaller OE components.

Not only that, but the durability aspect comes into play; the margin you have in terms of boiled brake fluid and cooked caliper seals is also much greater. Effectively, under the same use, a good BBK is under-stressed compared to the OE components.

This leads into your next excellent question about bias and clamping; you're discussing "brake torque" which is how much force the brake system applies to the axle. There is no need to increase brake torque whatsoever; with regular street tires, you can engage the ABS system already, which shows that the original brakes are already capable of generating more brake torque than the tires can handle. More brake torque will not help at all!

So what that means in terms of a good BBK is that the same brake torque is applied (if just a "front only" kit), or that all four wheels are generating the appropriate torque to maintain good bias. The benefit you're getting from the BBK is in it's increased component size, which is the fundamental strength of better heat management.

How does this compare to basic improvements you can do with the original components?

No matter what you do to an OE-size rotor, you're not increasing it's heat capacity... and you really should avoid cross-drilled rotors (that's an entirely different discussion, but despite marketing hype, cross-drilling will actually decrease your braking system's effectiveness and they do not aid cooling - it's a "race look" component that some think looks cool, and that's about it). The various methods of slotting are a good idea and help in terms of surface water evacuation (as when driving in rain) and freshening the pad face, but that's about it. Anything else in terms of plating is simply cosmetic.

Brake pads, however, are an area of great improvement. A good ceramic "enthusiast" pad like the Hawk Performance Ceramic or Akebono ProAct Ceramic will give better initial bite (how the brakes respond to pedal pressure) and will also have a higher maximum heat range. This is not to say they are pads you should use at a track - track use always means use track pads, there is no such thing as a good "dual purpose" street and track pad. Avoid the advertised "dustless" pads as these are commonly known to have a "wooden" pedal feel and decreased rotor life. It's also important that you use the same (or very similar) pads front and rear because different pad materials have different coefficient of friction ratings, which can substantially change the brake bias. If you know what you're doing, "pad tuning" is a useful tool for adjusting brake bias (most useful for track/race cars), read more about that- [ CLICK HERE ]

One thing you're certainly right about... BBKs do look cool! In addition to the benefits listed above, the "look cool" factor is certainly an acceptable reason to get a BBK. After all, it's your car, and making it look cool is certainly your privilege!

[sdiver68]

In my racing experience, cross-drilled rotors do help, and aftermarket brake pads with SS brake lines and a racing brake fluid (changed often) will solve 99% of your braking issues.

Not that a BBK is not a good idea, but it's really overkill for 99% of drivers considering BMW's come stock with really good brakes, considering performance alone. In fact, I wish more track enthusiasts would have less effective brakes so I wouldn't have to worry as much about them parking it on corner entry! :

However, they do look great and as was said above this may be reason enough to go with a kit.

[Rob * UUC Motorwerks]

Originally Posted by sdiver68

In my racing experience, cross-drilled rotors do help,

What exactly do you race?

Cross-drilled rotors were originally designed to reduce rotor weight. That's an odd concept to sell to a street user, so the industry came up with this "enhanced cooling" myth.

There are often heated debates about whether rotors should be drilled or not, which I frankly never understand... the problems, proofs, and examples of the downside to drilled rotors is overwhelming, and without proof of benefit.

The reality is that in terms of cooling, a conventional vented rotor without drilled holes cools better and has a more consistent cooling spread across the entire surface.

The rotors that I am recommending people avoid are the type that are a standard rotor design that is then simply drilled. This is different than a rotor that is designed with holes in the first place. As far as I know, no aftermarket rotors fall into this category... the only "designed-in" holes are the original equipment rotors from BMW, Porsche, and a few other marques. Beyond that, rotors that are simply "drilled" are prone to heat-induced stress cracks, eventually resulting in catastrophic failure of the rotor. This is principally due to the interruption of the metal grain structure formed during casting, creating a "stress riser" affected by differential temperature. The OE drilled rotors have a hole pattern that is stress-analyzed to the rotor's internal vane structure, and sized/chamfered to mnimize the stress riser effect. BMW Motorsport uses such rotors on the E46 M3 Competition Package, Z4 M Coupe, and E60 M5 (and likely on the new M3 when released).

If you examine the BMW brake system (and look at the racers using brake cooling ducts), you will see that the rotors have a central inlet on the back side of the rotor. This is designed to take cooling air in at the center and literally act as a centrifugal air pump to move that air through the rotor, cooling it evenly throughout the entire radius. Cross-drilling this type of rotor "short circuits" the cooling path, allowing all the cooling air taken in at the backside/center to exit frontside/center... never getting to the extreme radius, which is the hottest area in need of most cooling.

The only form of cross-drilled rotors that should ever be used are those that are designed that way... not the same as a solid-face rotor that is drilled. Rotors that are designed with holes often have a different internal vane structure that takes the holes into account, allowing for proper cooling.

Originally Posted by sdiver68

Not that a BBK is not a good idea, but it's really overkill for 99% of drivers considering BMW's come stock with really good brakes, considering performance alone. In fact, I wish more track enthusiasts would have less effective brakes so I wouldn't have to worry as much about them parking it on corner entry! :

Ooh, but how many times have we seen beginner students not "read" their brake feedback and cook them at the end of a long straight? That's a major pucker moment there, and one likely to result in a tow truck visit!

- Rob

[mikem]

My stock E90 330mm set up was pants, all it takes is one stop from 100+ down an off ramp to a roundabout where you sudenly had to brake harder near the end because the car in front didn`t go through a gap or a car comes around fast unexpectedly and your really having to stamp on the pedal.With the BBK initial bite is superb and with a little heat they get better, I went for Black as I wanted to keep them low key but everywhere I go, I get people staring down at them at the lights

Can only agree about drilled rotors, OK for track cars where brakes are reg. stripped down, inspected and replaced but it`s not practical on everyday drivers. Obviously discs that are cast with holes already in them are an exception but most people I know with M3`s have replaced stock cross-drilled with slotted ones.

[picus]

So here is a question that can probably be explained to me easily - the stock 335i rotors are 348mm in the front; and I often see BBKs sold for the 335i with *smaller* front rotors (or the same size). Is the quality of a bbk rotor so superior that the size makes such a small difference? I'm in the process of reading Rob's site, so odds are this question will be answered for me by the time someone posts, but I thought I'd ask.

To add to this, I see on UUC's site it's often mentioned that their bbk (or pbk) has 8-15% more rotor diameter compared to an M3, but this isn't the case for a 335i.

[Rob * UUC Motorwerks]

Originally Posted by picus

So here is a question that can probably be explained to me easily - the stock 335i rotors are 348mm in the front; and I often see BBKs sold for the 335i with *smaller* front rotors (or the same size). Is the quality of a bbk rotor so superior that the size makes such a small difference?

What I think you might be seeing is kits designed for the 330/325 and then being adapted to the 335.

Rotor size is only one part of heat management and the brake torque calculations. Piston size, pad dimensions, and even pad material are all critical parts.

Although larger rotors are part of heat management in the entire brake system, they are just a single part... fixed multi-piston aftermarket calipers will have several advantages over the floating single-piston OE caliper. These include larger pad area, fixed design that eliminates the floating caliper's mushy guide bushing, better heat dissipation in the aluminum body compared to the OE iron body, and in some examples, stainless steel pistons instead of aluminum pistons (stainless steel pistons do not expand and bind as aluminum pistons can, which improves pedal feel/modulation and lengthens service life).

I'm in the process of reading Rob's site

What you may notice on the UUC website is that our E90 BBK is specifically designed for 330/328/325/323 models only... we're not offering that configuration for 335. This is because the components are designed around the specific technical details of the 330 and 325 models - and which is also why the 330 can use just the front-wheel kit, but we recommend the 325 uses the 4-wheel kit for correct bias. We're very particular on every little detail for all models.

The 335-specific kit that UUC will offer shortly will take into account the specific hydraulic and bias requirements of that model.

- Rob

[picus]

Originally Posted by Rob * UUC Motorwerks

What I think you might be seeing is kits designed for the 330/325 and then being adapted to the 335.

Rotor size is only one part of heat management and the brake torque calculations. Piston size, pad dimensions, and even pad material are all critical parts.

Although larger rotors are part of heat management in the entire brake system, they are just a single part... fixed multi-piston aftermarket calipers will have several advantages of the floating single-piston OE caliper. These include larger pad area, fixed design that eliminates the floating caliper's mushy guide bushing, better heat dissipation in the aluminum body compared to the OE iron body, and in some examples, stainless steel pistons instead of aluminum pistons (stainless steel pistons do not expand and bind as aluminum pistons can, which improves pedal feel/modulation and lengthens service life).



What you may notice on the UUC website is that our E90 BBK is specifically designed for 330/328/325/323 models only... we're not offering that configuration for 335. This is because the components are designed around the specific technical details of the 330 and 325 models - and which is also why the 330 can use just the front-wheel kit, but we recommend the 325 uses the 4-wheel kit for correct bias. We're very particular on every little detail for all models.

The 335-specific kit that UUC will offer shortly will take into account the specific hydraulic and bias requirements of that model.

- Rob

Ah, I didn't realize you guys were going to do a specific 335i kit; I'll look forward to that. Thanks for the post.

[mikem]

Rob, will the 335 use the same calipers ?(I can see me trading by the end of the year)Looks like they could easily accept a bigger a rotor and even my carriers have plenty of room to adjust the caliper further out.

[obLu]

Thanks for the awesome info Rob!

[sdiver68]

Originally Posted by Rob * UUC Motorwerks

What exactly do you race?
- Rob

In addition to being a long-time car track and autoX addict, I retired from racing a couple of years ago, I was a semi-pro motorcycle roadracer. My main race bike was a GSXR600. All of our bikes have factory cast holes in the discs.

Your claim that cross drilling versus factory casting is directly contradicted by Brembo:

Are discs with cast-in-place holes better than cross-drilled discs?
Brembo has extensively studied and tested cross-drilling versus casting the holes in place and found no significant effect on performance or durability.

[Rob * UUC Motorwerks]

Originally Posted by mikem

Rob, will the 335 use the same calipers ?(I can see me trading by the end of the year)Looks like they could easily accept a bigger a rotor and even my carriers have plenty of room to adjust the caliper further out.

No, the 335 kit will have completely unique parts.

- Rob

[Rob * UUC Motorwerks]

Originally Posted by sdiver68

I was a semi-pro motorcycle roadracer. My main race bike was a GSXR600. All of our bikes have factory cast holes in the discs.

The stresses on motorcycle rotors pale in comparison to car rotors... and even the rotor design is very different. To review the obvious, a 3500lb car places much more stress on it's brakes than a 400lb motorcycle. Motorcycle rotors are barely more than sheets of iron, and they are directly exposed to cooling air at all times. That's very different than a thick car rotor enclosed within a wheel. Just the fact that there can be dramatically different temperatures in different zones of a car rotor clearly defines how thermal stresses differ from a relatively even-temperature motorcycle rotor.

(I do know a bit about bikes, too... although not doing anything commercially, my current bike project involves fitting the largest BMW race-spec motorcycle brakes to a BMW-based custom.)

Your claim that cross drilling versus factory casting is directly contradicted by Brembo:

I generally prefer more than a one-line "FAQ" answer to questions like this, which is why I prefer the competition car in-depth information provided by Wilwood, who quite simply are the largest manufacturer of competition brake systems and rotor components in the USA:

"Caution on drilled rotors: There is a common mis-perception that rotors are drilled to improve cooling. The reduced mass of a drilled rotor will dissipate its retained heat quicker, but it also builds up heat at a much faster rate. The decision to use drilled rotors should be solely based on the merits of the lower rotating and unsprung weight, and not for improved cooling. It is not wise to use drilled rotors in sustained high heat on hard braking tracks unless the team budget affords a high frequency of rotor and brake pad replacement."

"In categories where every ounce and thousandths of a second count, drilled rotors provide maximum weight reduction. For heavier cars, or cars competing in bracket or throttle stop categories, the additional mass in the solid face rotors provides higher thermal stability and will increase the service life of the rotors and pads."

Now when a company tells you not to buy one of their products because it's not suitable for your type of use, they earn my respect in a very big way. There's no marketing involved... just the plain facts.

By the way, remember my first post where I said "There are often heated debates about whether rotors should be drilled or not"?

- Rob

[sdiver68]

Originally Posted by Rob * UUC Motorwerks

I generally prefer more than a one-line "FAQ" answer to questions like this, which is why I prefer the competition car in-depth information provided by Wilwood, who quite simply are the largest manufacturer of competition brake systems and rotor components in the USA:

"Caution on drilled rotors: There is a common mis-perception that rotors are drilled to improve cooling. The reduced mass of a drilled rotor will dissipate its retained heat quicker, but it also builds up heat at a much faster rate. The decision to use drilled rotors should be solely based on the merits of the lower rotating and unsprung weight, and not for improved cooling. It is not wise to use drilled rotors in sustained high heat on hard braking tracks unless the team budget affords a high frequency of rotor and brake pad replacement."

"In categories where every ounce and thousandths of a second count, drilled rotors provide maximum weight reduction. For heavier cars, or cars competing in bracket or throttle stop categories, the additional mass in the solid face rotors provides higher thermal stability and will increase the service life of the rotors and pads."

Now when a company tells you not to buy one of their products because it's not suitable for your type of use, they earn my respect in a very big way. There's no marketing involved... just the plain facts.

By the way, remember my first post where I said "There are often heated debates about whether rotors should be drilled or not"?

- Rob

Fair enough, I appreciate your insight, even if I have reservations about the need for a BBK on the 3 series BMW.

[ksfrogman]

Great info, Rob. Thanks.

[WilyB]

Originally Posted by Rob * UUC Motorwerks

... and you really should avoid cross-drilled rotors (that's an entirely different discussion, but despite marketing hype, cross-drilling will actually decrease your braking system's effectiveness and they do not aid cooling - it's a "race look" component that some think looks cool, and that's about it).

Darn, I was "that" close to purchase that kit from you!



Now that I understand how wrong I was, I expect a huge discount from UUC to help you unload them...



PS: I then read your explanation about how BMW cross-drill its rotors... Thanks for the great stuff - and PM me that incredible discount!

[Rob * UUC Motorwerks]

Originally Posted by WilyB

Darn, I was "that" close to purchase that kit from you!

Now that I understand how wrong I was, I expect a huge discount from UUC to help you unload them...



PS: I then read your explanation about how BMW cross-drill its rotors... Thanks for the great stuff - and PM me that incredible discount!

Of course, when BMW provides the rotors, it's okay! These rotors are designed to be perforated.

[SV Concepts]

Originally Posted by Rob * UUC Motorwerks

Of course, when BMW provides the rotors, it's okay! These rotors are designed to be perforated.

Are Brembo's rotors not designed to be perforated? Why is it that Brembo supplies Ferrari, Lamborghini, Porsche, Maserati, AMG, and others with cross-drilled rotors? Why is it that the finest performance cars in the world (Ferrari Enzo) use cross-drilled rotors? Surely the designers of the Enzo care more about performance than looks on the brakes, no?

Also, I would like to clarify on something you said... Wilwood is most likely the largest manufacturer of braking systems in the US... but that is because they are one of the few ones in the US. This does not mean that their products are the best-selling in the US. They do make a good kit, though, despite the fact that they're better known in the American Muscle market.

JL

[Rob * UUC Motorwerks]

Originally Posted by Jlevi SW

Are Brembo's rotors not designed to be perforated? Why is it that Brembo supplies Ferrari, Lamborghini, Porsche, Maserati, AMG, and others with cross-drilled rotors? Why is it that the finest performance cars in the world (Ferrari Enzo) use cross-drilled rotors? Surely the designers of the Enzo care more about performance than looks on the brakes, no?

You know better than to ask that question - you've been in the business long enough to know the answer!

The OE equipment perforated rotors are made in a different way than aftermarket drilled rotors. Depending on the rotor, many of the OE perforated rotors are cast perforated, meaning the holes are cast into them. This retains the uninterrupted internal structure, leaving a much stronger part.

As far as OE... you may not have been aware of a Mercedes service campaign ("silent recall") to replace cracking drilled rotors. And, of course, take a look at any drilled rotor that's been used hard even on a street car, even a Porsche, you will often see the micro-cracks starting. Here's a picture I took right in our parking lot - [ CLICK HERE ] - not Brembo, but another popular BBK.

Aftermarket drilled Brembos are often not even made by Brembo... they are simply Brembo blanks that another company drills. Yes, Brembo does offer some perforated rotors, but not in all fitments and they are not always what is offered by vendors.

Also, I would like to clarify on something you said... Wilwood is most likely the largest manufacturer of braking systems in the US... but that is because they are one of the few ones in the US. This does not mean that their products are the best-selling in the US. They do make a good kit, though, despite the fact that they're better known in the American Muscle market.

There are more aftermarket brake caliper manufacturers in the US than in the rest of the world combined! To name just a few besides Wilwood, we've got Aerospace Components, Coleman, Howe, Lamb, Mark Williams, Outlaw, Red Devil, Sierra, SSBC, JFZ, Strange, Brakeman, US Brake... the list goes on and on.

I believe Wilwood actually is the best-selling aftermarket brake manufacturer in the US... and on more real racecars in the US than any other brand. In our narrow Euro-market world, we don't see the huge quantities of Wilwood brakes going on all sorts of other cars, and yes, that certainly does include the American muscle car market. In that particular market, 600hp and 4000lbs is common, and the braking needs are greater than our lightweight 250hp Euro rides.

[FirstClass]

Originally Posted by Jlevi SW

Why is it that the finest performance cars in the world (Ferrari Enzo) use cross-drilled rotors? Surely the designers of the Enzo care more about performance than looks on the brakes, no?

Well it sure isn't for cooling purposes.

[spacedogg]

Great info Rob...very informative.

[normtrum]

Originally Posted by Rob * UUC Motorwerks

What I think you might be seeing is kits designed for the 330/325 and then being adapted to the 335.

Rotor size is only one part of heat management and the brake torque calculations. Piston size, pad dimensions, and even pad material are all critical parts.

Although larger rotors are part of heat management in the entire brake system, they are just a single part... fixed multi-piston aftermarket calipers will have several advantages over the floating single-piston OE caliper. These include larger pad area, fixed design that eliminates the floating caliper's mushy guide bushing, better heat dissipation in the aluminum body compared to the OE iron body, and in some examples, stainless steel pistons instead of aluminum pistons (stainless steel pistons do not expand and bind as aluminum pistons can, which improves pedal feel/modulation and lengthens service life).



What you may notice on the UUC website is that our E90 BBK is specifically designed for 330/328/325/323 models only... we're not offering that configuration for 335. This is because the components are designed around the specific technical details of the 330 and 325 models - and which is also why the 330 can use just the front-wheel kit, but we recommend the 325 uses the 4-wheel kit for correct bias. We're very particular on every little detail for all models.

The 335-specific kit that UUC will offer shortly will take into account the specific hydraulic and bias requirements of that model.

- Rob

Rob - any updates on the 335i kit by UUC? The web site has being saying "coming soon" for quite some time now. Thanks.