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[yoogene]

trying to figure out if it's worth it to cross drill or drill slots into a set of some stock brakes rotors...and anyone know where it can be done and how long it takes?

[Macktastic]

man, i would just go buy some new ones.

[editionPOS]

Generally it is not a good idea to drill stock rotors.  This can cause them to crack around the holes with use.  Real crossdrilled brakes are cast that way and are not drilled at all.  This doesn't mean that a lot of them that you buy aren't just drilled stockies but that is really not the right way to do it.  Under use extreme enough to necessitate drilled rotors you would probably see them fail.  Slots are a little better strength wise but are easier to buy than make.  Even then they are probably unnecissary.  But if it is the look you are after then I would just buy some rather than do it myself.  You will spend more in quality drill bits than you would in just buying some already drilled or slotted.

[greggearhead]

What Justin said.  You will also really screw up the balance of the rotors unless you do it on a mill with a degree wheel.  Buy some.  

We used Rabbit front spindles and brakes on the Lotus race car, and we used hand-drilled solid rotors because, well, the owner was a cheapass.  They worked fine for autocrossing, but I wouldn't recommend it for a road car or track car.  And yes, they cracked, as will any holed rotor.  Last several sets of cast-in holes Porsche rotors I have seen have had cracks, and they are about the best available for normal chumps like us.

[yoogene]

wow, ok, good to know. i'm just checking to see if it was a worthwhile mod for better cooling purposes...and i'm asking on behalf of brakes that aren't currently on the car yet.  :wink:

[SoFarKingFast]

Go to www.stoptech.c om and read up on brakes.  Their FAQ section has some very good info on everything concerning brakes.

You will find out that slotted rotors do the same thing as drilled, but have a much higher tolerance to resist cracking.  Drilled are basically just for looks.

[greggearhead]

Go to www.stoptech.c om and read up on brakes.  Their FAQ section has some very good info on everything concerning brakes.

You will find out that slotted rotors do the same thing as drilled, but have a much higher tolerance to resist cracking.  Drilled are basically just for looks.

I hate it when I hear stuff like this.  In one year I ran x-drilled, slotted, plain (normal internally vented) and the brembo atom-slot things.  

There is a real difference in braking behaviors when the brakes are taxed - most people will never know becuase they don't run anything else back-to-back, or they replace worn out crappy brakes with new (whatever upgraded rotors) and think they are the best because of the improvement.  

The following is my experience, not scientific fact:
X-drilled really do help with cooling at the limit, but where they shine most of all was in snow and water crossings - instant braking force again, where any other style didn't get braking again until the water was heated/squeegeed off the rotors.  

Slotted didn't like the high temps nearly as well as the x-drilled, but did seem to reach operating temperature more quickly - a real plus if you are using higher temp range pads.  

The funky-pattern slots didn't seem to do much either way.  

Any of these will not help NEARLY as much as a larger rotor and/or caliper setup.  If you need better brakes for a higher hp application, go bigger first.

[SoFarKingFast]

Oh well, guess I am wrong.

[Macktastic]

Dang, Greg had a little something in his coffee this morning !

 :birdie:

[Scott]

[greggearhead]

No Ryan, you aren't wrong, but the information you read, in my opinion, is misleading.  Anytime I am reading something from a company selling something, a red flag goes up.  Hell, I saw that kind of stuff in the industry all the time.  Sorry if it sounded like I was jumping on your case - I didn't mean to.

[SoFarKingFast]

No Ryan, you aren't wrong, but the information you read, in my opinion, is misleading.  Anytime I am reading something from a company selling something, a red flag goes up.  Hell, I saw that kind of stuff in the industry all the time.  Sorry if it sounded like I was jumping on your case - I didn't mean to.

Well, I was lead to believe it was true due to the fact that they sell slotted rotors for less than drilled, and they still still recommend the slotted.

[greggearhead]

If their cost to manufacture slotted is less than the cross-drilled (likely) and they have to deal with fewer returns/disgruntled customers with cracks eminating from the x-drilled holes, the information they provide would steer customers to that assumption.

There's a billion things that go into choosing brakes.

Aside from the points greg made, keep in mind that when you drill a brake rotor, you remove surface area. And its that surface area that contacts the pad for braking. So by drilling, you effective reduce the swept area of your brakes for the benefit of gas dispersion.

Slotted and drilled having nothing to do with cooling but they have everything to do with cutting the gas layer at the contact point.

...too much complexity to discuss right now.

[Jesus]

blah.... I got your swept area  :wink:

[yoogene]

wow, so those audi guys are talking out of their ass about the cooling behaviors of drilled/slotted? i can understand the surface area being beneficial, but if there isn't any real benefit for doing it, is it just for show?

personally, i'm more into the "stock...but not" way of modding and i guess it'll be better to just keep the brakes that i just got.

[Scott]

Was this too fucking hard to understand?   :cool:

[Jesus]

Was this too fucking hard to understand?   :cool:

Is this too hard for you to stick in your mouth and shut up?  
   :shock:  :shock:

wow, so those audi guys are talking out of their ass about the cooling behaviors of drilled/slotted? i can understand the surface area being beneficial, but if there isn't any real benefit for doing it, is it just for show?

When most brake pads get hot, they produce a gas which can get trapped in between the pad and the rotor surface (a phenomenon known as outgassing). The presence of the gas inhibits the contact of the pad to the rotor, causing a hard pedal with signifigant friction loss. The purpose of the slots or holes is to "cut away" the gas layer as the rotor spins, ensuring continuous contact of the pad and rotor.

Crossdrilled rotors are lighter, but have less swept area. Slotted are a bit heavier, but are just as effective. Cooling is generally accomplished through the vented portion in the center of the rotor. Weight is often saved by using aluminum "hats", or 2 piece rotors. But, they're mad expensive.

Stopping power is the ability of the braking system to dissipate mechanical energy into heat energy. There is a certain balance between brake size, piston configuration, master cylinder size, and pad selection (among other things) to achieve optimal braking in certain situations. Race brakes may not get hot enough during daily driving to be effective and stock brakes will often fade after a few heat cycles on a track.

Once you determine your addplication, you then chose your equipment. For what you want to do, I'd go slotted with a more aggressive pad.

[bfcase]

Ignoring my avatar - the physics of braking are unstudied by myself and I am not qualified to take sides.

However, should anyone want them I do have a pretty complete line of Zimmerman cross-drilled rotors for most VW and Audi (and many BMW and Porsche; while in start-up mode I am focusing, because they are most familiar to me, on standard OEM VW and Audi parts for now but we do carry lots of BMW, Mercedes and Porsche stuff {as well as Volvo and Saab but we won't go there : ) }).

Send me your model and year application, the replacement part number if you know it and I'll be happy to quote anyonea good price - depending upon your take on cross-drilled rotors per this thread - smart or dumb enough to buy them.

I'll get to listing them on my site eventually (the only ones there now are for 16V applications) but I carry many, if not most, Zimmerman cross-drilled rotors for VW and Audi as well as Pagid, Mintex, Jurid and Textar pads (standard application - I don't have the super - racing formulations).

I also do not have slotted rotors yet.

OK - now please continue with the fighting, names-calling, put-downs and questionings of sexual orientation.

What a great forum : )

[greggearhead]

Absolutely agree with the decreased swept area of an x-drilled or slotted rotor - simple fact.  Agree with the out-gassing phenomenon.  However, the greatly increased surface area (overall) and direct passage to the cooling air channels of a x-drilled rotor have to help with cooling.  There is no way around it.

Its a distinct possibility. I can't picture the dynamics of the airflow in my  head.

[Scott]

I can't picture the dynamics of the airflow in my  head.

slacker

[editionPOS]

The point of drilled/slotted rotors is for releasing gas buildup, not cooling.  Vents in the rotors are for cooling.  Cooling is an issue because of warping and fatique not better braking.  Brake pads generally work better when hot.  Of course there are limits and selection of brake pads should include the type of driving you do.  If it is a track car where you will be on them enough to need slotted or drilled rotors as well as track/ hi-temp pads you will not like their performance on the street.  If you choose street pads and take them on the tracck they will fade when pushed hard partly due to the gas buildup.

[The Asshole]

OK - now please continue with the fighting, names-calling, put-downs and questionings of sexual orientation.

What a great forum : )

ok where is the Quotes section....

carry on.