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georgios

Cross drilled rotors.....a design flaw?

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I'm driving a 2003 C4s. I was recently checking out my rotors and pads and my freind who is also a car mechanic mentioned the fact that some after market rotors have beveled holes in order to reduce the microfractures. Is this true? If so, is this something I could have done to my current or new OEM rotors?

Thanks for any input

George

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I'm driving a 2003 C4s. I was recently checking out my rotors and pads and my freind who is also a car mechanic mentioned the fact that some after market rotors have beveled holes in order to reduce the microfractures. Is this true? If so, is this something I could have done to my current or new OEM rotors?

Thanks for any input

George

Hi, yes it is true. Naa, really not necessary, unless you are autocrossing. The temps won't get too high and it won't cycle at all so your factory drilled should do fine. The holes are mostly there to reduce fade by releasing the byproduct material and gasses from hard braking. HTH

Edited by ViolaGT3

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I'm driving a 2003 C4s. I was recently checking out my rotors and pads and my freind who is also a car mechanic mentioned the fact that some after market rotors have beveled holes in order to reduce the microfractures. Is this true? If so, is this something I could have done to my current or new OEM rotors?

I don't think the beveled holes will change things much. If you are just driving the car on the street, the rotors will be fine. If you are driving it hard on the track or autocross, cracks will form at the holes. The holes will also act a a cheese-grater and cause grooves in the pads and rotors.

IMHO, the holes are there mostly for appearance. Modern pads do some out-gassing when they are first getting bedded in but after that, it's not an issue. The holes may also improve the initial action of the brakes in the wet but in general, braking in the wet is very much limited by tire traction rather than braking force.

post-449-1226385682_thumb.jpg

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Another thing to remember about the beveled holes is that this beveling will soon dissappear as the rotor wears.

As for the holes being necessary or not or possibly just cosmetic, I would go with the belief that Porsche would not put them there is the adversly affected braking...

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Another thing to remember about the beveled holes is that this beveling will soon dissappear as the rotor wears.

As for the holes being necessary or not or possibly just cosmetic, I would go with the belief that Porsche would not put them there is the adversly affected braking...

HERE HERE!!

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IMHO, the holes are there mostly for appearance. Modern pads do some out-gassing when they are first getting bedded in but after that, it's not an issue. The holes may also improve the initial action of the brakes in the wet but in general, braking in the wet is very much limited by tire traction rather than braking force.

There's an interesting white paper from the SAE that may just surprise you: 2006-01-0691, The Effect of Rotor Crossdrilling on Brake Performance.

///Michael

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Now that's a teaser if there ever was one ... without spending $14, what were the high-level (non-copyright-violating) conclusions ?

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IMO, I have experienced better braking across the board on all the systems I have used both full Brembo and Willwood conversions as well as just aftermarket rotors. My pads when crossing would not fall victim to glazing nearly as often which lead to better performance and pad life, as well as increased rotor life/durability. You'll find that you do not run into warping issues nearly as much if at all. Another thing noticed when your brakes are hot and get wet you would lose a considerable amount of braking capability with a blank rotor. To touch on the before mentioned that pads do not gas out as much as in the past, partially true. Before they were comprised of the same compounds, today there is a vast diversity amidst companies and brakepad lines. If you have an issue with brake dust collecting on your wheels then you have brake pad gasses. They attract to the surface of the wheel and adhere to it you can test it by taking any other powder material tossing it at your dry wheel and then doing 80mph. Then see how much is there? . . . . .

P.S. The beveling/chamfering is typically set to the specific tolerance of the rotors wear specs. ie if the beveling appears to be roughly only 1/8th of an inch deep then double that amount and check the replacement specs for your rotor. PRC eBay rotors do not count as they are usually from a smelting company in Shen Yang that said why not?

Geez, why do I know all this? . . . . . anyone know how to understand women?

Edited by ViolaGT3

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I don't think Porsche has ever stated that cross-drilled rotors improve brake "performance".

That's a good point, they really don't have to though. I haven't seen a Porsche race car that has not either had drilled or slotted if not both rotors? Not debating, merely stating my appreciation of them.

Loren is the best! :renntech:

Edited by ViolaGT3

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How about the Porsche RS Spyder?

No slots or cross-drilling.

Well now I have seen one. Are those carbon rotors? Good God man.

:notworthy:

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And on another note, I would like to keep the examples limited to those who use carbon steel brakes.

As it is not fair playing with Mr. Porsche. :lol:

Loren am I able to buy one of those?

Well I suppose it does not matter I doubt I could afford to buy it anyways. It's not worth my life.

The little lady would kill me. . .

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Wow,

thanks for all the input! I guess I'm staying with OEM rotors as is. I dont track the car, actually its quite difficult to find a descent track out her.

George

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How about the Porsche RS Spyder?

No slots or cross-drilling.

Well now I have seen one. Are those carbon rotors? Good God man.

:notworthy:

Porsche RS Spyder

"Two-circuit hydraulic braking system, six piston aluminum monobloc brake calipers, front and rear ventilated carbon (ceramic) brake discs, F: 380 mm diameter R: 355 mm diameter"

Last time I checked PCCB (the closest street version) was an $11,000 option and replacement rotors are about $4000 per axle pair ($8000 for all four).

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How about the Porsche RS Spyder?

No slots or cross-drilling.

Well now I have seen one. Are those carbon rotors? Good God man.

:notworthy:

Porsche RS Spyder

"Two-circuit hydraulic braking system, six piston aluminum monobloc brake calipers, front and rear ventilated carbon (ceramic) brake discs, F: 380 mm diameter R: 355 mm diameter"

Last time I checked PCCB (the closest street version) was an $11,000 option and replacement rotors are about $4000 per axle pair ($8000 for all four).

Naa, if I wanted to blow that kind of money I would of went ahead and bought that pansy 360 Modena Spyder.

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The RS Spyder are carbon fiber and composite hence the reason for no drilling. Cross drilling provides better support for high temp and high braking situtations to offset the off gasing. Street, probably doesn't do much.

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Now that's a teaser if there ever was one ... without spending $14, what were the high-level

(non-copyright-violating) conclusions ?

Two GM engineers tested 2-3 cross-drilled braking systems and 2-3 solid-face braking systems. The pictures blurred anything on the rotors that could identify the braking systems they tested. It's a 28 page analysis/report with quite a bit of technical mumbo-jumbo.

They made a few observations (including the obvious of cracks developing around the holes), but the one that pertains to my reply is that cross-drilled rotors do improve brake cooling over solid-face rotors. Furthermore, the cooling rate increases as speed increases.

Of course, rotor design also plays an important factor. It is possible to put too many holes in a cross-drilled rotor or place them ineffectively.

The SAE article is locked w/ DRM on my personal laptop. If anybody is interested, then I'll also summarize the other observations that they noted in their conclusion if I get some time this evening. In the meantime, somebody else on another auto forum has read the same paper; you can read his comments as well if you're bored: linky, linky

My personal thoughts is that Porsche designed their cars to use cross-drilled rotors; and what I mean by designed, I mean the rotor diameters for their brakes are oversized. If you took, say a Nissan 350z, a 3300lb car w/ < 12" rotors (at least 2003 non-Track models had < 12" rotors) and bought cross-drilled replacements w/o increasing rotor diameter, then yeah, you're asking for a world of hurt after a few hard track sessions. Another example, the E46 M3 CSL / Competition package has cross-drilled rotors, but they increased the size (diameter & width) of the fronts over your regular M3.

///Michael

Edited by Michael-Dallas

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How about the Porsche RS Spyder?

No slots or cross-drilling.

post-1-1226464399_thumb.jpg

How does slotting or cross-drilling affect integrity of those rotors? Maybe in the next decade, those 2 GM engineers will write another white-paper on them... if GM is still around by that time...

///Michael

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For the street flavor PCCB, they are drilled; I bet they are engineered just fine. Link

Edited by Anders0n||C4S

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Well speak of the devil, my CPO "welcome kit" came in the mail today, which was a little unexpected to say the least! It came with a leather luggage address tag and a shiny CPO keychain. More importantly, there is a booklet that has all nifty tidbits of trivia, one of which included the brakes:

Why are there holes in the brake rotors?

At Porsche we cross drill the rotors on our sports cars to help control their temperature. The cross-drilled holes dissipate water vapor, maximizing contact between the brake caliper and the rotor. They also help the brakes cool faster than a solid rotor. Cooler brakes stop in a shorter distance than hot brakes.

:)

///Michael

Edited by Michael-Dallas

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Now that's a teaser if there ever was one ... without spending $14, what were the high-level

(non-copyright-violating) conclusions ?

Two GM engineers tested 2-3 cross-drilled braking systems and 2-3 solid-face braking systems. The pictures blurred anything on the rotors that could identify the braking systems they tested. It's a 28 page analysis/report with quite a bit of technical mumbo-jumbo.

They made a few observations (including the obvious of cracks developing around the holes), but the one that pertains to my reply is that cross-drilled rotors do improve brake cooling over solid-face rotors. Furthermore, the cooling rate increases as speed increases.

Of course, rotor design also plays an important factor. It is possible to put too many holes in a cross-drilled rotor or place them ineffectively.

The SAE article is locked w/ DRM on my personal laptop. If anybody is interested, then I'll also summarize the other observations that they noted in their conclusion if I get some time this evening. In the meantime, somebody else on another auto forum has read the same paper; you can read his comments as well if you're bored: linky, linky

My personal thoughts is that Porsche designed their cars to use cross-drilled rotors; and what I mean by designed, I mean the rotor diameters for their brakes are oversized. If you took, say a Nissan 350z, a 3300lb car w/ < 12" rotors (at least 2003 non-Track models had < 12" rotors) and bought cross-drilled replacements w/o increasing rotor diameter, then yeah, you're asking for a world of hurt after a few hard track sessions. Another example, the E46 M3 CSL / Competition package has cross-drilled rotors, but they increased the size (diameter & width) of the fronts over your regular M3.

///Michael

Hmm, I would have to say that there is a little bit about Porsches(911) being engineered to do 180mph, and Z's set at about 150mph. I would think that sub 12" rotors on a 3300# car would desintigrate after s short time on the Autobahn. Wonder if the specs are different in Europe or Japan? That's an odd comparison. in my book of performance cars, a 350Z you would not find, nor it's competitor the Crossfire or the Z3/4. While they are sporty and 15-26 year olds love them you would more then likely destroy one of them if you did track it(consumer cars). My thoughts on the brakes for 911's is simply engineered to take what you throw at it. Switzerland, Germany, USA, Italy, Doesn't really matter which one. I have run into a few hills in a rental BMW 323 in Garmisch Germany before thart would have really appreciated Porsche brakes.

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Hmm, I would have to say that there is a little bit about Porsches(911) being engineered to do 180mph, and Z's set at about 150mph. I would think that sub 12" rotors on a 3300# car would desintigrate after s short time on the Autobahn. Wonder if the specs are different in Europe or Japan? That's an odd comparison. in my book of performance cars, a 350Z you would not find, nor it's competitor the Crossfire or the Z3/4. While they are sporty and 15-26 year olds love them you would more then likely destroy one of them if you did track it(consumer cars). My thoughts on the brakes for 911's is simply engineered to take what you throw at it. Switzerland, Germany, USA, Italy, Doesn't really matter which one. I have run into a few hills in a rental BMW 323 in Garmisch Germany before thart would have really appreciated Porsche brakes.

A short digression...

Well, back in the day, I had a 2003 350z Track model and my friend had a 2003 350z Touring model. My Track model had factory 12.75" rotors front and rear w/ Brembo 4/2 pot calipers while his Touring model had those sub 12" rotors w/ 2 pot sliding calipers.

On our first DE, he had braking issues (heavy pad and fluid fade) while mine held up ok except for the uneven deposition I got on the rotors. I simply had my rotors turned to remove the deposition while he upgraded to a 13" Stoptech BBK. A few DE's later, hairline cracks started developing on my solid 12.75" rotors. At $500 per factory rotor, the 350z Track model quickly lost its allure for a cheap track platform.

Granted that I had the rotors turned to remove the deposition, they were still w/in spec. But if I could crack solid rotors in a few DE's, just think what would happen if I slapped aftermarket cross-drilled rotors w/o increasing rotor width or diameter...

///Michael

Edited by Michael-Dallas

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Hmm, I would have to say that there is a little bit about Porsches(911) being engineered to do 180mph, and Z's set at about 150mph. I would think that sub 12" rotors on a 3300# car would desintigrate after s short time on the Autobahn. Wonder if the specs are different in Europe or Japan? That's an odd comparison. in my book of performance cars, a 350Z you would not find, nor it's competitor the Crossfire or the Z3/4. While they are sporty and 15-26 year olds love them you would more then likely destroy one of them if you did track it(consumer cars). My thoughts on the brakes for 911's is simply engineered to take what you throw at it. Switzerland, Germany, USA, Italy, Doesn't really matter which one. I have run into a few hills in a rental BMW 323 in Garmisch Germany before thart would have really appreciated Porsche brakes.

A short digression...

Well, back in the day, I had a 2003 350z Track model and my friend had a 2003 350z Touring model. My Track model had factory 12.75" rotors front and rear w/ Brembo 4/2 pot calipers while his Touring model had those sub 12" rotors w/ 2 pot sliding calipers.

On our first DE, he had braking issues (heavy pad and fluid fade) while mine held up ok except for the uneven deposition I got on the rotors. I simply had my rotors turned to remove the deposition while he upgraded to a 13" Stoptech BBK. A few DE's later, hairline cracks started developing on my solid 12.75" rotors. At $500 per factory rotor, the 350z Track model quickly lost its allure for a cheap track platform.

Granted that I had the rotors turned to remove the deposition, they were still w/in spec. But if I could crack solid rotors in a few DE's, just think what would happen if I slapped aftermarket cross-drilled rotors w/o increasing rotor width or diameter...

///Michael

Hi granted the Diameter is a big part of big braking, having cross drilled rotors would of helped in cooling efficiency that would of helped prevent the overheating that caused your rotors to crack. But you witnessed the difference between Porsche cost and sport car cost. Oddly enough I know alot of people who 1/4 mile quite well with tuner cars >10< sec. But their cars are weight reduced by and average of 500#'s and it does not envolve cycling the brakes. They do allright with simple Green Stuff pads and After-m's drilled rotors.

For those not in the know 1900# 2100 with driver Bertone X1/9 running a Dodge Turbo III Motor and A55 Tranny Pushing 630hp.

It's pretty quick, but keeps tearing the rear tower. 9.46@142mph. It cannot be driven on the street safely.

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