Why do 'supercars' use cross drilled and not slotted brake rotors

[TripleM]

Re: Why do 'supercars' use cross drilled and not slotted brake rotors

Shaun...
In GT3 Cup ( not the S nor RSR ), the entire 4 corners of discs are x-drilled.
The only thing I can deduce from this particular choice is because the Cup cars in their primary Carrera Cup series are all of the same cars competing and no team is allowed to change any of that.

 

[TripleM]

Re: Why do 'supercars' use cross drilled and not slotted brake rotors

The rear rotors look bigger than the front?

In the pics, they seem so or similar size but the official specs are
Front brake system: Six-piston aluminum brake calipers, inner-vented grey-cast iron brake disks 15.0 in./380mm in diameter
Rear brake system: Four-piston aluminum brake calipers, grey-cast iron brake disk, 13.1 in./332mm in diameter

 

[Shaun]

Re: Why do 'supercars' use cross drilled and not slotted brake rotors

yup jack, cos porsche is one of the big proponent of drilled stuff...no idea why.. maybe it is too late or too unpleasant for them to turn back - so it follows that their spec series would have it. the cup car races are all short duration and they can afford to switch rotors as and when needed.

are they a larger thicker rotor? or a standard road car part number?

 

[centurion]

Re: Why do 'supercars' use cross drilled and not slotted brake rotors

yup jack, cos porsche is one of the big proponent of drilled stuff...no idea why.. maybe it is too late or too unpleasant for them to turn back - so it follows that their spec series would have it. the cup car races are all short duration and they can afford to switch rotors as and when needed.

are they a larger thicker rotor? or a standard road car part number?

According to a webbie here: Drilled/Slotted Rotors....the reality...a good read - G20.net - Forums

Porsche is x drilled to:

1) Save weight
2) Holes FAR smaller than normal drilled, less stress.
3) Precision drilled to be across the internal cooling vanes
4) Holes not actually drilled? but cast in?

P crossdrilled is not like others ler...

 

[Shaun]

Re: Why do 'supercars' use cross drilled and not slotted brake rotors

According to a webbie here: Drilled/Slotted Rotors....the reality...a good read - G20.net - Forums

Porsche is x drilled to:

1) Save weight
2) Holes FAR smaller than normal drilled, less stress.
3) Precision drilled to be across the internal cooling vanes
4) Holes not actually drilled? but cast in?

P crossdrilled is not like others ler...

YET they still crack. You've been quite lucky not to have cracking possibly because non S is not that powerful or heavy and because you have good ducts? I'm not sure. On the higher power stuff, they do crack though.. guaranteed.

the point about weight doesn't make sense to me. you can save weight and material cost by casting and grinding the rotor to different dimensions..without drilling. The good aftermarket brake companies know and do this.

 

[kenntona]

Re: Why do 'supercars' use cross drilled and not slotted brake rotors

Founded on Brembo's website:

Are discs with cast-in-place holes better than cross-drilled discs?

Brembo has extensively studied and tested cross-drilling versus casting the holes in place and found no significant effect on performance or durability.

Why are there so many holes in a cross-drilled disc?

The number of holes in a cross-drilled disc is part of the engineered system. Brembo has done extensive testing with regards to the number of holes, their size, their location and their chamfering. This attention to detail is what truly sets Brembo apart in the world of braking. The same attention to detail that is delivered to the Ferrari Formula One effort is a component of the high performance program. The number of holes in a disc is in part a function of the size of the disc and the internal venting (if it is a vented disc).

What are the advantages of drilled and slotted discs?

The main advantages of drilled and slotted discs are the same: increased brake "bite", and a continuous refreshing of the brake pad surface. Drilled discs have the additional advantage of being lighter and running cooler. However, there are certain pad materials that should not be used with a drilled disc.


I am starting to think these are marketing bullshit, but done blatantly deceptive.......

 

[Shaun]

Re: Why do 'supercars' use cross drilled and not slotted brake rotors

and yet Brembo drilled stuff cracks all over the place even on pads that come with the kits

====

AP is more honest IMO

Disc grooves and sometimes cross drilling are frequently used on racing brake discs to clean the surface of the pad and allow gases produced to escape.
In doing so the friction characteristics are modified, different groove and & drilling patterns affect the friction characteristics in different ways, some affect overall friction and others the bite or release characteristics and therefore the best solution is not necessarily the same for each application.
AP Racing is constantly developing and refining disc face patterns. The most popular face types are shown below:-

P = Plain,
(No grooves or holes)
Mainly used on road applications
where low noise is vital​

G4, 8 12 & 24 = Grooved,
(Straight forward facing)
Digit specifies number of grooves per face.
Traditional style grooves.​

CG4, 8, 12 & 24 = Curved grooves,
(backward facing)
Digit specifies number of grooves per face.
New standard pattern.

CR4, 8, 12 & 24 = Curved grooves,
(backward facing, running out on outside diameter to clear debris.
Only used on thick wall discs).
Digit specifies number of grooves per face.​

D = Cross drilled,
drilled holes chamfered).
Still preferred with some pad materials but can compromise disc life.

GD = Grooved and drilled.
Usually used on road applications.​

RD = Radiused drilled,
(cross drilled but with a radiused run out to reduce noise and improve life compared with standard drilling patterns).
Mainly used for aesthetic reasons on road applications.

RA = J hook design.
Latest design gives improved bite and debris clearance and reduces distortion / vibration, outer grooves run out to outside diameter.​

N.B. Not all face types are available for every disc.

Disc Face Types

 

[TripleM]

Re: Why do 'supercars' use cross drilled and not slotted brake rotors

Shaun
They are different part numbers. The CUP Cars one are lighter than the street ones like fitted on std GT3s coz the Cup rotors (front) have got alu hat to reduce the unsprung rotational mass and yes, they are slightly larger too (380mm vs road car 350mm). The rear ones are slightly larger too than stock and both dont have alu hat...The body governing the series is so strict that the brake pads used have to be the same as well across all teams.

 

[Shaun]

Re: Why do 'supercars' use cross drilled and not slotted brake rotors

hahah yah and they don't even let you mount your own completely independent, very cheap, single channel data logger onto the car in testing even because it potentially raises costs for all competitors.. pfft.. good cost control though

 

[Shaun]

Re: Why do 'supercars' use cross drilled and not slotted brake rotors

Marc, someone recently bumped an ALMS thread on here and on it there is an actual photo of the Rahal Letterman M3 in actual track testing. It is not a press photo for Rays or Volks wheels like the one you posted.

Anyway one of the photos is this one http://farm4.static.flickr.com/3129/3235511656_755e04dc10.jpg

and it can be found in high resolution over here, along with many other closeups of both the front and rear brakes as run. BMW M3 GTR

So my view might have been correct

Marc, now going beyond an official test session to an official race weekend, here's a shot from Long Beach. Download the photo and zoom in on either wheel.. all slotted..

 

[Girettom]

Re: Why do 'supercars' use cross drilled and not slotted brake rotors

OK - I'm convinced that I'm happy with slotted myself.

But reading this thread again...it seems a bit far fetched that a company would drill their breaks to get a subtle marketing advantage. Do they (the manufacturers) really sell more cross-drilled than slotted (or open up a new market segment)?

If slotted breaks are really technically superior then there would be credible technical analysis behind it?

If drilled breaks were really that bad then surely a credible break manufacturer like brembo would not want to potentially sully their name with lots of failing rotors?

Also, if BMW NA were truly trying to wooo their customers, changing the rotors to drilled for a photo shoot seems like a fair amount of effort.

Perhaps cross-drilled is just a better application for mixed and wet weather, with the downside of cracking (like the choice between slicks and wet weather tyres). The compromise clearly discussed in earlier posts.

 

[iScoupe]

Re: Why do 'supercars' use cross drilled and not slotted brake rotors

wow great thread !
been using Brembo cross drilled with bad habit of washing car when is hot, the rotor was 9yrs old,
check regularly still no noticeable cracks till i sold off.

 

[Shaun]

Re: Why do 'supercars' use cross drilled and not slotted brake rotors

Do they (the manufacturers) really sell more cross-drilled than slotted (or open up a new market segment)?

Perhaps, still.. it's at the very least an additional segment for them.

If slotted breaks are really technically superior then there would be credible technical analysis behind it

Pad surface cleaning. The edge of the slots is very sharp and the reason slotted discs are more noisy and harder on pads. All this accomplished without cracking easily (unlike with holes)

If drilled breaks were really that bad then surely a credible break manufacturer like brembo would not want to potentially sully their name with lots of failing rotors?

Sure they would, because only 1% track, and majority love and are fine with bling and the odd one-stopper.

Also, if BMW NA were truly trying to wooo their customers, changing the rotors to drilled for a photo shoot seems like a fair amount of effort.

On racecars, swopping rotors (once assembled with hats) is literally a 3 minute job even on system not intended for quick swap. Some endurance racecars are specifically set up to be able to swap out the caliper and rotor together at once in under 1 minute, with no bleeding required. Just 2 bolts and 1 quick disconnect once wheel is removed as with a normal tire change. So really, not much effort for them. And the evidence shows that they almost certainly did so.

Perhaps cross-drilled is just a better application for mixed and wet weather, with the downside of cracking (like the choice between slicks and wet weather tyres). The compromise clearly discussed in earlier posts.

In road cars maybe, but in the wet I just drive slower and brake earlier. And when the sun comes out, no need to worry as much about cracking this and that when I head to track.

wow great thread !
been using Brembo cross drilled with bad habit of washing car when is hot, the rotor was 9yrs old, check regularly still no noticeable cracks till i sold off.

They only crack when put under lots of stress.. meaning under tracking or track-like conditions. The fact that the rotor can last 9 years means it probably has never been run hard in its life, or for a very short duration only.

 

[Racebred]

Re: Why do 'supercars' use cross drilled and not slotted brake rotors

my stock brakes on my 3200GT. It's a 4 + 2 pot system from Brembo. Notice the grime covering almost all the holes. Makes them irrelevant as it takes away the advantages of outgassing.

 

[888]

Re: Why do 'supercars' use cross drilled and not slotted brake rotors

Has there ever been a case where the rotors break apart because of hairline cracks ?

 

[Shaun]

Re: Why do 'supercars' use cross drilled and not slotted brake rotors

Yes. If left to grow they will crack... depending on the level of stress, all it takes is 2 major heat cycles from the point of being able to feel it with your nail, and they can crack all the way through.

 

[Darth Vader]

Re: Why do 'supercars' use cross drilled and not slotted brake rotors

wow great thread !
been using Brembo cross drilled with bad habit of washing car when is hot, the rotor was 9yrs old,
check regularly still no noticeable cracks till i sold off.

9 year old brembo,people still buy ? this recession is really deep.

 

[niteblu]

Re: Why do 'supercars' use cross drilled and not slotted brake rotors

my stock brakes on my 3200GT. It's a 4 + 2 pot system from Brembo. Notice the grime covering almost all the holes. Makes them irrelevant as it takes away the advantages of outgassing.

those look like minor hairline cracks forming around the drilled holes...



hmmm

 

[888]

Re: Why do 'supercars' use cross drilled and not slotted brake rotors

Yes. If left to grow they will crack... depending on the level of stress, all it takes is 2 major heat cycles from the point of being able to feel it with your nail, and they can crack all the way through.

The funny thing is I have a friend who has Brembos and his hairline cracks are worst that the one pictured above.
He still tracks his car heavily and nothing seems to happen but whenever I look at the hairline cracks I cringe because its so dangerous.

Thats why I asked whether they has been an actual case that it will break rather than assumptions.

cheers.

 

[Shaun]

Re: Why do 'supercars' use cross drilled and not slotted brake rotors

That's the problem with discussion involving subjective terms like "major" and "heavily", lacking actual quantities like masses, powers, heat energy and temperature, heat dissipation and rejection, material and hole properties. It is possible to work out it all out and run the tests, but who will pay for this proof, this quantification?

As mentioned earlier on this thread, there've already been 2 trackers here who recently missed trackdays due to cracked cross drilled brembos. One had a major crack to where the car was not trackworthy, and the other decided not to track because the radial cracks had grown too big for his comfort. IMO, your friend is not very wise if he is driving a high power high speed car around hard, trackday after trackday, with cracks growing (they will), not replacing them but waiting till they actually catastrophically fail.