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E46 (1999 - 2006)
The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

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  #26  
Old 01-21-2011, 11:54 AM
theruined theruined is offline
Cross Drilled Huh?
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Originally Posted by smolck View Post
He meant track as in "racetrack". I think old Bob-O is hinting at the fact that we have some very highly skilled drivers on here that can tear up a track with the best of em, and none of them have ever indicated that the stock rotors weren't up to the job.
I see, in that case, no I do not "track" it - sorry for the noobish response

The choice was not as much for "performance" (in the extreme sense of the word) as it is for longevity and durability...I have used stocks up until I went this route about a year ago and I won't go back to stocks just because I prefer the use and feel - the look is also a plus.

I have been looking to get into more of the track scene but I doubt I have the money to spend on modding my car for that - honestly wouldn't know where to start
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  #27  
Old 01-21-2011, 11:57 AM
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Originally Posted by theruined View Post
I see, in that case, no I do not "track" it - sorry for the noobish response

The choice was not as much for "performance" (in the extreme sense of the word) as it is for longevity and durability...I have used stocks up until I went this route about a year ago and I won't go back to stocks just because I prefer the use and feel - the look is also a plus.

I have been looking to get into more of the track scene but I doubt I have the money to spend on modding my car for that - honestly wouldn't know where to start
Most here will agree drilled rotors are eye candy. But we have yet to prove that drilled perform any better. In fact, most say they chew up pads faster than blanks. Anyways, stick with what works for you!
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  #28  
Old 01-21-2011, 12:03 PM
theruined theruined is offline
Cross Drilled Huh?
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Most here will agree drilled rotors are eye candy. But we have yet to prove that drilled perform any better. In fact, most say they chew up pads faster than blanks. Anyways, stick with what works for you!
I could see that, and I could also see how it matters not outside of actual racing...meh

Anyway I did have a question you could maybe help me answer about brake pads - I wrote it out in an earlier post on this thread...

What's the diff between the various pads out there? Any benefits/drawbacks vs. Stock?

Also brakes skipping on rotors when breaking over bumps - normal or no?
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  #29  
Old 01-21-2011, 12:48 PM
TerraPhantm TerraPhantm is offline
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Originally Posted by smolck View Post
Most here will agree drilled rotors are eye candy. But we have yet to prove that drilled perform any better. In fact, most say they chew up pads faster than blanks. Anyways, stick with what works for you!
In most cases, yea drilled rotors don't really offer a performance advantage. However, in the 330s case, the stock brakes really suck in the rain (at least mine did). Switching to the motorsport rotors fixed that.

The motorsport rotors are also a 2-piece floating design, which makes them considerably lighter and better at dissipating heat compared to the stock rotors
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  #30  
Old 01-21-2011, 01:20 PM
JonS2004330ci JonS2004330ci is offline
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OP sez he "wants to upgrade to cross-drilled rotors..." and "I don't do any racing...It's more for cosmetic reasons"...

OP: Here is a pic of my '04 330ci with the BMW Motorsport Cross-Drilled rotors (fronts) that I just installed this summer; did fronts & rears. Although I didn't go with red caliper paint, the silver paint I used (G2 Caliper Paint) gives the calipers a clean yet understated (and unpretentious) look.

Prices have dropped dramatically on the cross-drilled rotors over the past months, to boot!

Good luck!

Jon in Chicago
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  #31  
Old 01-21-2011, 02:19 PM
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Originally Posted by TerraPhantm View Post
and better at dissipating heat compared to the stock rotors
But then we have to argue about physics. A blank rotor has more mass and more surface area to better dissipate heat than a lighter rotor with less material and surface area.

I have read some pretty techy articles about this topic and it isn't as easy as saying "cross drilled have better ventilation so they cool better". There is far more to it than that.
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  #32  
Old 01-21-2011, 02:23 PM
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  #33  
Old 01-21-2011, 02:36 PM
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  #34  
Old 01-21-2011, 03:17 PM
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But then we have to argue about physics. A blank rotor has more mass and more surface area to better dissipate heat than a lighter rotor with less material and surface area.

I have read some pretty techy articles about this topic and it isn't as easy as saying "cross drilled have better ventilation so they cool better". There is far more to it than that.
Yep....solid rotors have more swept area for a given rotor size compared to a drilled rotor....greater swept area is like putting a larger rotor on the car. Of course, there are those who will respond with the old standby "Well, drilled/slotted rotors defeat the gas layer between pads & rotors", but no one has ever proven to me that the difference really amounts to much more than a few butterfly farts....
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  #35  
Old 01-21-2011, 03:45 PM
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Perhaps drilled rotors dissipate heat better, but aren't they far more prone to rusting, and then cracking? Wouldn't slotted be the best choice for daily drivers?
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  #36  
Old 01-21-2011, 03:48 PM
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Originally Posted by TerraPhantm View Post
However, in the 330s case, the stock brakes really suck in the rain (at least mine did). Switching to the motorsport rotors fixed that.
This i will agree with. When I first got my car and had stock pads, I was alarmed at how little braking power I had upon first application if the rotors were wet. Slotted rotors were recommended to me to solve the water problem, but after switching to Axxis Ultimate pads, that has been a non-issue for me.

I can see the argument for reducing unsprung weight too. A couple pounds at each corner is not trivial.
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  #37  
Old 01-21-2011, 08:00 PM
TerraPhantm TerraPhantm is offline
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Originally Posted by smolck View Post
But then we have to argue about physics. A blank rotor has more mass and more surface area to better dissipate heat than a lighter rotor with less material and surface area.

I have read some pretty techy articles about this topic and it isn't as easy as saying "cross drilled have better ventilation so they cool better". There is far more to it than that.
In this case, the better thermal characteristics are due to the floating nature and the directional vanes. I've had both brakes, the temperature difference after a hard session was remarkable.
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  #38  
Old 01-22-2011, 07:49 AM
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Originally Posted by TerraPhantm View Post
I've had both brakes, the temperature difference after a hard session was remarkable.
How many degrees? I'll assume same ambient temperature and other weather conditions.
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  #39  
Old 01-22-2011, 05:57 PM
TerraPhantm TerraPhantm is offline
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I wish I took precise measurements, but basically it was the difference between getting a burn/scar on my finger and not getting one lol. If I had to guess, I'd imagine the peak temperatures were similar, but that the motorsport rotors cooled down quicker and therefore had lower average temperatures.

It's too bad BMW doesn't make rotors w/ the best of both worlds: Two-piece floating design w/ directional cooling vanes while still having solid discs. The euro-spec E39 M5s actually had rotors like that, but I guess drilled rotors look "sexier" so they decided to start making those.
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  #40  
Old 01-25-2011, 10:09 AM
theruined theruined is offline
Cross Drilled Huh?
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Quote:
Originally Posted by smolck View Post
But then we have to argue about physics. A blank rotor has more mass and more surface area to better dissipate heat than a lighter rotor with less material and surface area.

I have read some pretty techy articles about this topic and it isn't as easy as saying "cross drilled have better ventilation so they cool better". There is far more to it than that.
I have to disagree and here's why...

Heat transfer is a function of surface area, and actually you may think you're decreasing the surface area by cross drilling but you're actually opening your rotors up even more by removing volume and creating more room for air to cool your brakes. Much like grooves and dents actually increase aerodynamicity (i.e. golf ball), this concept may be counter intuitive, yet by creating holes we must now add the additional cross-sectional area of the drilled hole in addition to the total area of the rotor. By drilling into the rotor we are only removing the TOP portion of the area calculation, but by creating a hole we are creating a 3D surface, instead of a 1D surface increasing the facets on which air can contact, thus increasing cooling efficiency.

An example would amount to the following: In the distilling industry packing towers are made with packing that has an increased surface area, or MORE holes...this is to allow for more contact between fluid and packing to separate distillates.

It is, however, arguable that this may not make much of a difference, or cause a decrease in performance, but it has been shown time and time again with multiple heat/fatigue tests that metals actually dissipate heat much more effectively if they are 1) of a lighter material (low density metals tend to have less magnetic/sparse atomic electrons, thus resist the transfer of energy more) 2) resist elastic deformation when a force is acted upon that surface in an angular fashion, thus the ability to decrease heat energy transfer better than

The issue here lies with #2 in the sense that lighter (or less dense) materials have a greater tendency to elastically deform and may even face permanent deformation when impacted under extreme heat. However, if you can understand the (low density) cross drilled rotors cool faster, they are less susceptible to heat warping/deformation and may even increase stopping power based on the fact that less heat due to friction may attribute to reduced brake slippage. Of course this all has to do with quality of product and integrity of manufacture.

In the end, I love the way they look on my car, and I don't have to track it in order to notice a difference because in most cases, an untuned car driving in the city wears on rotors much more (over a longer period of time of course) than a tuned track car. That's my reasoning behind the whole matter.

I would think reducing the gas barrier between brake and rotor has little to do with it...but they may have an argument at speeds in excess of 100mph...in most cases this is negligible.

And yes, making a rotor bigger does increase stopping power, so does increasing the proportional brake size - yet, I fail to see how a cross drilled rotor manages to under perform as far as stopping power goes...in the end it all goes to preference but I just thought I'd shed a little bit of light on the whole matter, no offense intended
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Last edited by theruined; 01-25-2011 at 10:11 AM.
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  #41  
Old 01-25-2011, 12:50 PM
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SJBimmer SJBimmer is offline
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Hard to compare swept area loss due to drilled rotors to additional benefit derived due to increased surface area for heat dissipation. All I know is that my stock brakes work fine even when I have worked them hard, and my car is probably the heaviest of all the E46 models.
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