Originally posted by BlackSleeper:
First off I'm not trying to knock you, just inquiring for more info.


No problem, that's what the board is for.
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Q:If drilled and slotted rotors do nothing for braking performance then why do they used them on the Lemans GT cars? There was an article link in a post awhile ago that explained this in detail, IIRC.


They don't. Its not used in either Le Mans or ALMS. in fact, most of the big guns run carbon-carbon, not cast iron. In carbon brakes, there are series of small dimples used for on the fly wear measurements. These are often mistaken for cross drilling.

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From what i have read,cross drilled rotors are made primarily for cars equipped with integrated "brake ducts" like Porsche's,BMW and Corvettes.



WHat you have read is wrong. Cross drilling was originaly implemented on racing vehicles in the 50's/60's due to pad outgassing. Because of the pad material of the day, those pads would heat up and release hot gasses from the pads. These gasses would cause a boundary layer which was difficult to compress and caused an artificial fade condition. Modern pads simply don't have this condition any longer. However, much like alloy wheels and rear spoilers, the "racing look" caught on, and became derigor in street performance vehicles.

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This channel of air forces its way from behind the rotor out through the holes, causing a cooling affect.


Not quite. Cooling effect is marginal, no street driver will ever notice the effect. The only noticible contribution of x-drilled rotors to most drivers is an improved first effectiveness in wet condtions....i.e. better bite in the wet. The only place that x-drilling shows any significant cooling effect is on applications of CCM or Ceramic Composite Matrix discs...ala Ferrari Enzo, Challenge Stradale, 575 GTC, F430. However, Ceramics have a tremendously different heat cycle and disipation method. Not relevant in this discussion.

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Yes they will probably eat up pads a lot quicker.


Not probably, will. THey are much more aggressive with friction material, as are slotted.

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I hear all the time "don't get Cross drilled rotors they will crack after a few months" well if you buy crap rotors, I'm sure they will, and if you don't have ture brake ducts you may be at more of a risk as well. If one were to buy Brembo rotors, "cross drilled by Brembo" they would be ok.


Well, as an engineer for Brembo, I certainly appreciate the good publicity. However, it is unwarented. Our x-drilled rotors will crack too. I know, I have tested them on the dyno and the track. All cross drilled rotors will crackunder track stress and heat cycles, as the drilling creates a stress concentration point...it can't be avoided. There is a reason that Porsche, Ferrari, Lamborghini etc all run solid faced rotors on their race cars. However, under street conditions it is rarely a serious condition. In addition, a proper disc design ( hole size, chamfer, relation to venitng, etc.) can help prolong the life of a drilled disc.

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The failure rate tests these rotors go through is like 300%,engineers design them this way so covers the legality issues of being liable etc.


Correct, parts are put through an intesnive DV/PV test plan. However, the duty life of a drilled rotor isn't as long as a solid faced part.

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please feel free to correct me. Once again I'm not trying to argue, just my $.02




No problem. X-drilled rotors are misunderstood and mismarketed all over the place. Given today's technology and braking systems, x-drilled comes down to one thing...marketing. Its all about the bling. For a track vehicle, its just not suited. For a street vehicle, it rarely poses a problem. In fact, most people will see small cracks around the edges of a drilled rotor and immeadiately scream "failure, get them off, oh the horror!" Bull-sh!t. Cracks on a cross drilled are not necessarily a problem. As long as a crack doesn't exceed 2/3's of the braking surface, or touch an edge...no problem. Same for a solid faced rotor.

As I said, it all comes down to the bling. However, given all of that, I would have no problem placing x-drilled discs on my own car. It rarely sees track time, and I like the look. When my current discs need replaced, x-driled may be the replacement. But then again, I get mine for free...so I'll take what I can.

Cheers,
-Todd

Very few of life's problems can not be solved with the reasonable application of more horsepower!