http://forums.bimmerforums.com/forum/showthread.php?p=13603616

Rob,

I have interest in a front brake upgrade and have a question for you on this kit. I don't mean to sound obnoxious, but thought my question may be shared with others on the forum.

When comparing your kit to the other popular kit on the market, yours seems to have a very nice caliper in the Alcon, but the rotors are what detracts from your kit in my mind. For the same price point, rather than a true two piece floating 332mm in my choice of solid, slotted or cross drilled rotor, your kit only has the option of stock blank and the OEM Motorsport cross drilled two piece in 325mm.

Can you comment on the advantages of your kit?

This is an excellent question! This answer applies only to the E36 and E46 applications.

The advantages with the Alcon calipers is simple; build quality and performance that exceeds any other brand's similar components... we're talking about firmer / more controllable pedal, resistance to caliper deformation, and high-temp capability.

To be blunt about it, the Alcon is really in a different league than competing "street sport" kits. The similarity in price is due to simple factors; we work directly with the Alcon factory, no multi-tier reseller profits, no giveaway promotion budget to make up, and we don't have the expense of shipping rotors from overseas.

Even though the Alcon is an "exotic" caliper, you still enjoy the benefits of common pad availability - all of the 4-piston fitments share pad shapes with Porsche and Brembo applications, so you can get practically any pad material you want.

But to discuss your concerns about the rotors... In all reality, from a simple standpoint of basic measurements, a couple of millimeters here or there in thickness or diameter is not having any significant impact on the fundamental brake torque calculation or thermal capacity of the system.

The basic math: between 325mm and 332mm is a mere 0.0192% difference in brake torque. For reference, the change in pad coefficient of friction in common street pads just going from 275F to 450F results in a brake torque change three times that difference.

From a floating standpoint, I have yet to see a design better than the BMW Motorsport rotors. I am going to copy some text from our website:

Genuine BMW Motorsport floating rotors as used on the European-spec versions of the M3 and M3 CSL:

Suitable for street, track, or race use. The "floating" design separates the central rotor hat from the outer disk, allowing the disk to expand radially with heat and limiting heat transfer to the hub. The theory is that the rotor will not "cup" or distort under extremely hot race use, resulting in better braking performance and better rotor and pad wear. Additional benefits include lighter weight, approximately 1.5lbs per rotor.

BMW Motorsport uses a "radial floating" design where the floating connectors between the rotor hat and the rotor disk connect in the center of the disk between the inside and outside face planes using a radial (straight out) pin. It's a very interesting construction that is not simply "assembled" but built all together at the foundry level.


http://www.uucmotorwerks.com/pbc/rotors/radial1_small.jpg (http://www.uucmotorwerks.com/pbc/images/radial1.jpg) http://www.uucmotorwerks.com/pbc/rotors/BMW_MOTORSPORT_ROTOR_small.jpg (http://www.uucmotorwerks.com/pbc/images/BMW_MOTORSPORT_ROTOR.jpg)
(click pics for larger views)

What's even better is that the Motorsport floating rotors are a "complete replacement" design - you get a new hat every time you replace the rotor, at a much lower cost from BMW Motorsport than the "disk only" cost of aftermarket rotors with other BBKs. When you start comparing costs, especially for race use, this really adds up. For an interesting ongoing-costs comparison, see this page: [ CLICK HERE (http://www.uucmotorwerks.com/alcon/costs.htm) ]

Beyond that, there are alternate choices as well, such as the Performance Friction Pin Drive floating rotors, economical 1-piece rotors, or rotors of any brand that are designed for the E46 M3.

But here is the more interesting part which I think you will like; in the very near future, UUC will be offering a 330mm x 32mm floating rotor option/upgrade. If you have the kit with 325x28 rotor, the upgrade to the 330x32 rotors is just the cost of the rotors... we will provide the bracket parts necessary at no charge. You will be able to switch back and forth between 325x28 and 330x32 whenever you want, so you can keep a 1-piece "street" set mated to your street pads, and the larger/thicker "track" set mated to your track pads.

Please let me know if you need any further information or clarification!

- Rob

Rob,

Care to comment on the brake bias of a two wheel versus a four wheel BBK? Also, how do you properly achieve correct brake bias when you're using the same pad and rotor sizes front and rear? Finally, any guess on the rotor cost for the upcoming 330x32 rotors?

Thanks

Rob,

Thanks for the response.

Do you have comparison data on the calipers? How much stiffer are they? To be honest, from my perspective, the value in your kit seems to be the calipers, not the rotors.

I appreciate the theory that larger rotors aren't necessarily better due to the added rotating weight and that the BMW Motorsport rotors are well designed. Is there an option for solid E46 Motorsport rotors like the E36 Motorsport rotors I have currently on my E36 M3? I don't want cross drilled rotors. Will your new rotors be available in solid and slotted or are they the CSL rotors?

Mike

Rob,

Care to comment on the brake bias of a two wheel versus a four wheel BBK?

Brake bias remains unchanged in the applications where we have specific kits. Keep in mind that the front kit for one specific application is not necessarily the same as the kit for another application, each kit's piston sizes are tailored for the specific chassis.

Regardless of the application, the components chosen for that application will retain the original bias f/r percentage within very tight limits, or have minor tweaking one way or the other as we may have tested superior performance.

Keep in mind that increasing brake torque is not the primary advantage of a BBK... the reasons for a BBK involve greater thermal capacity, greater resistance to heat-induced characteristic changes or damage, improved pedal feel and modulation, and sometimes weight reduction.

One thing we do for each application is to match the hydraulic requirements of the calipers to the master cylinder already in the car.

Also, how do you properly achieve correct brake bias when you're using the same pad and rotor sizes front and rear?

Another excellent question.

Brake bias is determined using a multi-part formula with many prime factors and several secondary factors based on a comparison of front brake torque to rear brake torque. In rough terms, the primary factors are rotor diameter, pad height, total piston volume, hydraulic pressure, pad coefficient of friction, etc. Changing any one of these changes the brake torque. You can have identical rotors and pads, but changing the piston sizes bigger or smaller will dramatically change brake torque. For example, rough bias numbers for a front-engine car with 50/50 weight balance is in the neighborhood of 65% front, 35% rear bias. Look at the E46 M3 as a case in point. Rear rotors are actually larger by 3mm, pad height is nearly the same, yet the appropriate 65/35 bias is achieved... alll through piston size. That's exactly the way we do it also.


Finally, any guess on the rotor cost for the upcoming 330x32 rotors?

I hesitate to quote an exact price at this time before the numbers are crunched, but they should be competitive with other brands, somewhere in the low-$400 and mid-$500 range for a complete pair. Replacement rotor disks, about half that. To repeat, these are "guesstimates" and may be significantly higher or lower when product is available.


Do you have comparison data on the calipers? How much stiffer are they? To be honest, from my perspective, the value in your kit seems to be the calipers, not the rotors.

That isn't anything that we publish, it's internal testing data.

I appreciate the theory that larger rotors aren't necessarily better due to the added rotating weight and that the BMW Motorsport rotors are well designed. Is there an option for solid E46 Motorsport rotors like the E36 Motorsport rotors I have currently on my E36 M3? I don't want cross drilled rotors.

No, BMW does not make them that way. I do understand your concerns about perforated rotors, and normally we would not recommend a generic drilled rotor.

However... after having used the perforated BMW Motorsport rotors on our own racecars for over two years, I can say from experience that we have never seen the structural cracking effect. This may have to do with a few factors including the specific alloying and chamfered hole design in the BMW rotors.

Of course, any rotor used under race conditions will develop surface "thermal shock" cracks. What we have done with several sets, mostly heavily-used race sets, is analyze the crack propagation to determine if they are common surface cracks or deep structural cracks. The basic idea is to test the depth by milling the rotor surface away in small increments and measuring the remaining crack width. The results between the Motorsport perforated rotors and other brand floating plain-face rotors has been indistinguishable, all cosmetic surface cracks only.


Will your new rotors be available in solid and slotted or are they the CSL rotors?

They are completely purpose-made rotors, not an OE application. Primarily they will be offered in a slotted design, but there is no reason we could not offer plain also.

- Rob