[Dieselstation]

Cross Drilled Brakes vs. Slotted Brakes

which are better?
the whole thing started when i took a picture of these brakes on an M3..
picture: http://www.stolemyinter.net/uploads/IMG_2776.JPG
and some guy said whoever owns that car is an idiot for getting cross drilled rotors.



Modified by Dieselstation at 12:21 AM 7-3-2004

 

[winkosmosis]

Re: Cross Drilled Brakes vs. Vented Brakes (Dieselstation)

Aren't all cross drilled rotors vented? All I know is slotted are no good for street cars because they wear the brake pads faster for some extra "bite".

 

[Dieselstation]

Re: Cross Drilled Brakes vs. Vented Brakes (winkosmosis)

sorry.. meant to say slotted. but yeah.. that's the argument.

 

[RJetta8V]

Re: Cross Drilled Brakes vs. Vented Brakes (winkosmosis)

The heavier a rotor is, the more heat it can store. The more heat a rotor can store, the better the car stops. If you drill the rotors, you are decreasing the weight, therefore, you are decreasing the efficiency of the brakes.

 

[Dieselstation]

that only applies to carbon fiber brakes because they need to be warmed up before usage. on normal brakes, the hotter the brakes are.. the more likely you'll experience brake fade and the more likely your brake fluids are going to expand and therefore not work as good. also metallic rotors and pads need cooling for maximum efficiency
so you want MORE surface area, but LESS heat.


Modified by Dieselstation at 12:31 AM 7-3-2004

 

[DohRado]

Re: (Dieselstation)

aren't drilled rotors prone to cracking?

 

[BerryBoy3504]

Re: (DohRado)

Quote, originally posted by DohRado »

aren't drilled rotors prone to cracking?

i've heard that.....wondering about that myself

 

[ijcameron]

Re: (BerryBoy3504)

It's true that there is less thermal mass in a cross-drilled rotor, but it's also true that there is more surface area for cooling in a cross-drilled rotor.
So which is better? Well, I know which one LOOKS better...

 

[nemesisjetta00]

Re: (BerryBoy3504)

Quote, originally posted by BerryBoy3504 »

i've heard that.....wondering about that myself

i had a set of brembo crossdrileds on my jetta for about 2 years and never had cracking issues

 

[ijcameron]

Re: (nemesisjetta00)

Quote, originally posted by nemesisjetta00 »

i had a set of brembo crossdrileds on my jetta for about 2 years and never had cracking issues

Some of the more expensive rotors have the holes cast in, some are drilled after the fact.
I think the real reason for cross-drilling is lost in history - it used to be that as barke pads became superheated they created a gaseous layer between the pad and rotor - the holes released the gas. With modern pads, this is all but eliminated.

 

[C_walsh]

Re: (nemesisjetta00)

I had crossed drilled breaks on my mkiii GTI for about 2 years and as far as I know the current owner still has them on the car.

 

[CFster]

Re: (C_walsh)

I think slotted rotors do the job better - as far as dissipating the gas.
I too, have heard that drilled rotors are prone to cracking.

 

[Obin Robinson]

Re: Cross Drilled Brakes vs. Slotted Brakes (Dieselstation)

all you need to know:
- vented is always better than solid
- slotted is better than cross drilled
- a well-designed braking system is better than one done "for looks"
i've asked the brake question many times to various racers and the answer always comes back that it's all about the pad compound, the rotor quality, and the brake cooling.
obin

 

[ijcameron]

Re: Cross Drilled Brakes vs. Slotted Brakes (Obin Robinson)

Quote, originally posted by Obin Robinson »

i've asked the brake question many times to various racers and the answer always comes back that it's all about the pad compound, the rotor quality, and the brake cooling. obin

I've read stuff by brake engineers that state that efficient brake ducting (with the ducts directed at the vented center of the rotor) is the best thing you can do to improve the effectiveness of braking (good rotors and pads notwithstanding).

 

[toyotagardner]

Re: Cross Drilled Brakes vs. Slotted Brakes (ijcameron)

well it's still confusing, because many race cars have solid rotors with very good ventilation to them, where as ferarri and other top exotic manufacturers have cross drilled rotors for their street cars. Do the equivilent race cars have the same rotors or do they go back to solids for real racing? Do even ferrari and porsche succum to the,"well they look like they have better performance" idea, that I and most likely others have? There was a thread about this a while ago, plus I think obin had a pic of a brake rotor that was thick, used for racing.

 

[AZGolf]

Re: Cross Drilled Brakes vs. Slotted Brakes (toyotagardner)

I've noticed a lot of real race cars run with smooth-faced rotors. Even the prototype-style cars and stuff.

I'd say probably 70% of all the cars at the last Grand American race I went to had smooth faced rotors. The rest were slotted in some way, such as this Porsche. I don't recall seeing a single race car with drilled rotors.

 

[winkosmosis]

Re: Cross Drilled Brakes vs. Slotted Brakes (AZGolf)

I don't understand the vented rotors that aren't drilled. Where does the air come from that should be pulled through by the fins?

 

[TDI Vroom]

Re: (Dieselstation)

Quote, originally posted by Dieselstation »

that only applies to carbon fiber brakes because they need to be warmed up before usage. on normal brakes, the hotter the brakes are.. the more likely you'll experience brake fade and the more likely your brake fluids are going to expand and therefore not work as good. also metallic rotors and pads need cooling for maximum efficiency so you want MORE surface area, but LESS heat.

But the problem is with less material in the brakes (aka turning your rotors into swiss cheese), it will heat up faster because you have the same amount of heat energy being distributed over less volume. I don't know how significant the effect is though.

 

[Obin Robinson]

Re: (ijcameron)

Quote, originally posted by ijcameron »

I think the real reason for cross-drilling is lost in history - it used to be that as barke pads became superheated they created a gaseous layer between the pad and rotor - the holes released the gas. With modern pads, this is all but eliminated.

originally cross-drilled rotors were designed for hillclimb cars. Porsche used them in the 1960s because they were light and efficient. they were also never intended to be permanent as they'd throw them away after each hillclimb.
obin

 

[TMTuned99.5Golf]

Re: Cross Drilled Brakes vs. Slotted Brakes (winkosmosis)

Quote, originally posted by winkosmosis »

I don't understand the vented rotors that aren't drilled. Where does the air come from that should be pulled through by the fins?

Well, from my past experiance with heatsinks, the great the surface area the more chance there is for air to move over the surface to remove that heat build up. Though, there is certain limitations to which must be met. The distance between filns generally can be no greater than the surface of the fin. Well, that applied when I was making a few prototype heatsinks for Tektronix that is.
With cross drilled rotors I can see the benefit with the air going through the holes to be sucked or blown out the center section. With slotted, the air is sucked intot he slot as the rotor is going under the pad and the only escape being the end of the slot.
I have been told by some peopel that cross drilled is meant for racing purposes as with the venting and such. I currently have Zimmerman cross driled rotor and axis carbon kevlar pads on my car and I can't believe the stopping power I have.
As a note about the MB with the flat faced rotors, we can't assume that they are using the same composition of rotor that we use on our car. Another thing to think about with a flat faced rotor, there is more surface area of contact to use when at the higher speeds, possibly a reason why they did that.

Just my $.02 on that one.