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Motorsports & Track Forum
From Auto-X to Trackday to Racing and Professional Motorsports this is the place to discuss making BMWs fast

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Old 03-12-2006, 12:27 PM   #21
Rob Levinson * UUC Motorwerks
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Quote:
Originally Posted by vaio76109
Rod, you never replied to this....
I thought post #12 covered that:
http://forum.e46fanatics.com/showpos...8&postcount=12

But to elaborate further, the water issue is compounded by splashes, puddles, and even deep puddle submergence.

As the link in that post indicates, Mercedes-Benz obviously feels it's an issue.

- Rob
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Old 03-12-2006, 12:30 PM   #22
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Quote:
Originally Posted by Rob Levinson * UUC Motorwerks
I thought post #12 covered that:
http://forum.e46fanatics.com/showpos...8&postcount=12

But to elaborate further, the water issue is compounded by splashes, puddles, and even deep puddle submergence.

As the link in that post indicates, Mercedes-Benz obviously feels it's an issue.

- Rob
How exactly is water going to "stick" to a hot rotor thats spinning(centrifugal force)?
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Old 03-12-2006, 12:39 PM   #23
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Quote:
Originally Posted by vaio76109
How exactly is water going to "stick" to a hot rotor thats spinning(centrifugal force)?
Is that a serious question?

Next time you're driving in the rain and come to a stop, jump out of your car and look at your wheels. Are they dry? No. They're spinning at the same rpm as your brake rotors (and since they're a larger diameter, the centripetal force is greater at the extremity).

If you've never felt "funny" braking in the rain, you're either not paying attention or are simply not driving in the rain.

I think you should go argue basic physics and hydrodynamics with the engineers at Mercedes.

- Rob
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Old 03-12-2006, 03:19 PM   #24
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Yes it's a serious question.

Once again you've dodged my question and posted some rubbish, nevermind.

-Greg

PS-Do you talk down to people all the time in person, or it is just an online thing? Oh, and before you ask, yes it's a serious question.

Last edited by vaio76109; 03-12-2006 at 03:21 PM.
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Old 03-12-2006, 09:34 PM   #25
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Quote:
Originally Posted by vaio76109
Yes it's a serious question.

Once again you've dodged my question and posted some rubbish, nevermind.

-Greg

PS-Do you talk down to people all the time in person, or it is just an online thing? Oh, and before you ask, yes it's a serious question.
I don't get what's going on here. I've been giving you serious answers with information backed up from a reputable source. I'm not dodging any question - you're missing the answer. Are you reading these posts or not?

Don't talk to me about "talking down" - your part of this conversation has been, to put it quite simply, a bit on the rude side. Please keep the conversation civil.

I post information from Mercedes-Benz about their feeling a necessity to have an active water removal system. Q.E.D., water on the rotors is (and obviously so to most people) a concern.

How the water stays on a spinning rotor is also a Q.E.D. situation, simply by looking at a similar spinning item, your wheels. A brake rotor is a semi-porous surface, and water clings to moving surfaces - even those with even less porosity. Water clings to your wind-swept windshield (even defying the efforts of a sub-optimal wiper blade), your paint, your wheels, tires, anything exposed.

Water simply clings, and even moves by itself to cover more of a surface. Consider the concept of a meniscus, the propensity for water to climb the surface of a container (water forms a concave surface in a test tube or other container as we all learned in high school physics). This has to do with surface tension, which acts on concave menisci to pull the liquid up. This phenomenon is intrinsic to water (and other liquids) along the same lines as transpirational pull and capillary action, both situations where water exerts force or movement in a practically active manner.

Now, on to the practical aspects of brake rotors and how water adversely affects braking, surely you've heard the word "hydroplaning"? This term is generally referred to two automotive situations, the first being the tires "riding up" on water and losing all friction contact, the second being the dynamically identical situation of brake pads riding up on surface water... or even more importantly, hot rotors during braking which encounter water (such as a splash or a puddle) and then generate steam, which expands and can actually push the pads away from the rotor - again, losing all friction contact. This situation is avoided with a slotted rotor which gives the water or steam a quick "escape path" so the pad does not lose (or can more quickly regain) contact with the rotor.

I hope that finally gives you the deeper insight to understand the situation.

- Rob

Last edited by Rob Levinson * UUC Motorwerks; 03-12-2006 at 10:07 PM.
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Old 03-12-2006, 11:36 PM   #26
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Quote:
Originally Posted by vaio76109
Yes it's a serious question.

Once again you've dodged my question and posted some rubbish, nevermind.

-Greg

PS-Do you talk down to people all the time in person, or it is just an online thing? Oh, and before you ask, yes it's a serious question.
......................... !!

pls have some respect when you are asking a question and expecting an answer....
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Old 03-12-2006, 11:51 PM   #27
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Old 03-13-2006, 09:42 AM   #28
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Quote:
Originally Posted by vaio76109
How exactly is water going to "stick" to a hot rotor thats spinning(centrifugal force)?

The key element which Greg is asking is a hot rotor.

On some tracks rotors seldom get below 100C (that's 212F for you Farenheight boys), which causes water to simply vaporize upon contact with the rotors.

Furtheremore, since heat is a radiant property, and air does have its own heat capacity value, water can vaporize even before reaching the rotor.

So, I think that if I ask: "what purpose does discussing water evacuation have to do when dealing with rotors that are already blazing hot from track usage since this is a track subforum and not a daily driver section" I hope to be capturing the essence of his question.

Greg, please feel free to let me know if I missed something.

There is something that's been bothering me though. Rotors are laced with organic deposits from the pads. These organic deposits are hydrophobic, so how would water stick to a surface that is overall non-polar ?


I'd like to make a personal mention about winter. Living in an area where -40C (-40F once again) is not uncommon during the winter time, I can say that after the initial braking, we don't really need to warm up the pads every so many minutes (short of doing continuous highway driving for extended periods of time), because we are using pads that work in the cold: HPS or Ceramics.
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Old 03-13-2006, 10:02 AM   #29
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Quote:
Originally Posted by Asmodeus
So, I think that if I ask: "what purpose does discussing water evacuation have to do when dealing with rotors that are already blazing hot from track usage since this is a track subforum and not a daily driver section" I hope to be capturing the essence of his question.
That may very well be the case. I was answering the question, as I did initially, as to the value of slotting in overall (including street) usage.

Quote:
There is something that's been bothering me though. Rotors are laced with organic deposits from the pads. These organic deposits are hydrophobic, so how would water stick to a surface that is overall non-polar ?
Pads apply a multi-component layer... and the more aggressive it is, it's often more metallic. I don't think that it becomes actively hydrophobic with any pad usage. Another rel-world QED example - your rotors are rusty after a rain or wash after sitting for just a few hours.

- Rob
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Old 03-13-2006, 10:13 PM   #30
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ASMODEUS, yes that is what i was talking about. Thank you very much.

I am stepping out of this thread. I wont be posting anymore(unless I feel compelled to), but I will be reading.
-Greg
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Old 04-02-2006, 11:32 PM   #31
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Don't know about the other rotors, but the UUCs work just fine. We just broke the HP track record at PIR by over 2 seconds a lap using the UUC slotted front rotors.



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Old 04-02-2006, 11:42 PM   #32
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I gotta side with Rob on this one.... have you guys never felt that 'oh crap' moment in the pouring rain when you step on the brakes and nothing happens, then the brakes grab all of a sudden???? I am not saying that slotted rotors would absolutely fix that, but it is possible to have water on the rotors.
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Old 04-05-2006, 04:41 PM   #33
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I live in a desert so water ain't much of a factor and I don't track my car. I want slotted for looks only. Is there a reason, other than wasting money, to not get slotted just for everyday driving? With my wheels you can see the rotors and calipers real easy so I'm looking to improve looks.
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Old 04-06-2006, 11:31 PM   #34
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Is there a reason, other than wasting money, to not get slotted just for everyday driving?
Not that I can think of.

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Old 04-07-2006, 05:09 PM   #35
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There's been a lot of debate over slotted/non slotted, cross drilled/slotted - and it came down to this, slotted are better than cross drilled on a track b/c they are stronger and are less susceptible to cracking under high stress (aka - this will only happen on the track). Otherwise, cross drilled is better for street applications b/c they allow more air to flow through the rotor thus cooling it (but they may crack between the holes under track conditions). And finally, slotted or cross drilled are a hell of a lot better than OEM rotors to rid glaze & water & gas from between the pad and rotor. And anyone who's ever driven through a large puddle and then stepped on the brakes knows what I'm talking about when first water is coating your rotors and then steam gets trapped between the pad & rotor b/c of the heat associated w/braking.

My favorite - cross drilled, they look sick and you seriously have to have a pure racer to break them.

Don't mean to step on any toes, I'm no braking engineer but this is the best explanation I've ever received on the issue

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Old 04-07-2006, 05:50 PM   #36
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Originally Posted by sebpop
Otherwise, cross drilled is better for street applications b/c they allow more air to flow through the rotor thus cooling it.
False.

BMW vented rotors (front on all, rears on M3/M5 and largest-engine 5s and 7s) are specifically designed to draw in air from the center (fronts often draw in the air on the inner side, rears generally from the outer side) and centrifigually pump the cooling air through the rotor, venting at the outermost edge.

Drilling defeats this by allowing the air to escape immediately through the central holes, never making it to the outer area.

As the outer edges get the hottest (larger diameter measurement equals faster circumferential speed), this results in a very poor cooling pattern.

So you see, drilling does not have any technical benefit - actually a deficit. It's "advantage" for street use is strictly cosmetic, for people who like how they look.

Use 'em if you want to, but don't do so under the misconception that they work better.

- Rob
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Old 04-07-2006, 06:02 PM   #37
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Originally Posted by Rob Levinson * UUC Motorwerks
False.
BMW vented rotors (front on all, rears on M3/M5 and largest-engine 5s and 7s) are specifically designed to draw in air from the center (fronts often draw in the air on the inner side, rears generally from the outer side) and centrifigually pump the cooling air through the rotor, venting at the outermost edge.
This is the point of the rotor backing plates. It brings air from the front of the car via ducting, generally 3", and uses this air to flow through the rotor veins additionally cooling the rotor. The helps alot with brake fade and will also make your pads last longer. However, its not really a street item as you wont want unwanted debris coming in contact with your rotors.
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Old 04-08-2006, 09:15 AM   #38
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This is the point of the rotor backing plates. It brings air from the front of the car via ducting, generally 3", and uses this air to flow through the rotor veins additionally cooling the rotor. The helps alot with brake fade and will also make your pads last longer. However, its not really a street item as you wont want unwanted debris coming in contact with your rotors.
Yes.

I think we're agreeing, but let's clarify for those reading along - some are asking about track use, and some about street use...

A racecar or track car brake ducting system runs a big speed-pressurized air tube from the front bumper and ducts it to a replacement backing plate with a duct fitting. Ideally, this cooling air is primarily directed at the central vent intake of the rotor - that works better to supplement the original "air pump" design, although some duct designs center it on the rotor face which work less well as the inner side only of the rotor is cooled more than the outer.

Street cars usually don't run brake ducts, and most owners would not want to for several reasons; modifications to the front bumper (or removal of the fog lights), the maintenance of the ductwork itself (which gets knocked around with suspension movement) and the cost of installation (replacement backing plates require disassembly of the hub/spindle, plus the labor of a brake service, plus the labor of the duct install and bumper modifications or special direct-fit inlets).

Completely worth it for a track car, without a doubt.

- Rob
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Old 04-08-2006, 06:07 PM   #39
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Originally Posted by Rob Levinson * UUC Motorwerks
replacement backing plates require disassembly of the hub/spindle
Not if you use tin snips to remove them

And for the new rotor backing plates most are designed so you dont have to remove the hub.
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Old 04-12-2006, 10:01 AM   #40
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Originally Posted by Rob Levinson * UUC Motorwerks

Very beneficial - better pedal feel, more durable... and since brake lines are really a consummable item anyway and should be replaced every few years, SS lines are often a less-expensive option than new OEM.

Details and what qualities to look for in SS lines:
http://www.uucmotorwerks.com/ss_brake_lines/

- Rob
I am only interested in street application and have a question. In a cold weather area, are there increased condensation issues if you use SS Brake lines?
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