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Old 10-16-2004, 11:49 PM   #121
luvinimports
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Re: Cross drilled rotors, better or not?

plus just lifting on an f1 car provides so much downforce it helps to slow and stick the cars threw the corners

i was thinking wouldn't a slotted rotor, like slice the break pad sorta if that makes sense?
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Old 10-18-2004, 08:09 AM   #122
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Re: Cross drilled rotors, better or not?

not really because the pad would never have the space to be pushed down into the slots.
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Old 10-19-2004, 08:53 AM   #123
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Re: Cross drilled rotors, better or not?

Quote:
Originally Posted by 911GT2
Well obviously it depends on the thickness of the rotor to make the surface area. Here, I'll explain what I mean:

Area (let's just do the area of one cross-drilled hole ok?

NON CROSS DRILLED

Area=2(pi)(radius)^2 (the 2 is for each side of the rotor)

CROSS DRILLED

Area=2(pi)(R)(l) (the l is the thickness of the rotor)

Now, to find out where the areas equal each other, let's make the two areas equal:

2(pi)(radius)^2=2(pi)(R)(l)

Cancel out the repeating terms and you come up with r=l

So as long as the rotor is thicker than the radius of the hole, you end up with ultimately more surface area. And note that that radius of the holes is usually very small and while the rotors aren't always really thick, they're thicker 90% of the time, especially considering that cross-drilled brakes are usually aftermarket and therefore thicker.

There, I've explained myself.
4*pi*r^2 - 4*pi*ri^2 is the approximation of the surface area, where ri is the outer diameter. 4 surfaces - the two exterior pad-facing sides, and the inner two inside the vented area.

4*pi*r^2 - 4*pi*ri^2 - 4*k*pi*rx^2 + 2*k*pi*r*h is the approximation of the surface area of the cross-drilled rotor, where k is the number of drilled holes, rx is the radius of each drilled hole, and h is the thickness of each side of the rotor (not including the vented area).

Now, let's assume a 25cm outer diameter rotor, with a... 10cm inner diameter (for the hat or some such). Let's also assume 100 holes, each 0.5cm in diameter. The rotor faces will be 0.75 cm thick (the total rotor thickness doesn't matter).

Area of non-cross-drilled rotor = 156.25pi - 25pi = 412 square cm
Area of cross-drilled rotor = 412 - 4kpirx^2 + 2kpirh

= 412 - 4(100)pi(0.25)^2 + 2(100)pi(0.25)(0.75)
= 412 - 78.5 + 118
= 451

Therefore, cross-drilling a rotor can add extra surface area, though a respectable amount of swept rotor area is taken away.

Cross-drilling adds more surface area if the rotor sides are thicker (the additional surface area from the walls of the holes), because the ends of the cylindrical holes stay the same in area, but the area of the round wall of the cylinder increases.

Note that not all surface area cools equally.


PLEASE PLEASE do correct me if my math is bad!
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Old 12-04-2004, 08:06 AM   #124
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Re: Cross drilled rotors, better or not?

We build race vehicles. (Mainly for Road Racing use). Slotted, drilled rotors will NOT do anything for a street vehicle. Obviously larger swept rotors can provide better stopping power, but with street tires who cares? You will experience tire adhesion loss long before you reach any limits of the stock rotor. If you are short track oval racing or road racing, The above impoved rotors do help. (and in most case are actually needed). Constant hard braking (as often as 5 or 6 times a lap in road racing from 100+mph heats the rotors/pads and causes them to gas. This gas results in a barrier between the pad and rotor, causing brake fade. (Something that I doubt any street or drag racer has ever experienced unless he as total junk on the car or is pulling a trailer. ) Cross drilling can also help cooling by prividing more external surface area.

Also, brakes will also not last as long when using slotted drilled rotors. Unless you have race compound sticky tires, drive at high speeds and brake hard every 20 seconds for several minutes at a time and don't have ABS,.... Don't waste your money on cross drilled expensive rotors.
Unless you just want to look "cool".

Jim
SR Racing
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Old 04-14-2005, 08:58 PM   #125
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Re: Cross drilled rotors, better or not?

ok, now i'm posting this for two reasons

one: i haven't been on in a little while and i like getting attention lol

but Two (and most important): i think som ething here needs to be just bluntly put in stead of putting math formulas here!

i mean really, skyline, silver, and moppie, had everything finally sorted out and then holes and surface area had to be thrown in again.

let's make this short and blunt eh?

YES, the holes will add surface area, but what KIND of sruface area, THAT'S THE KICKER RIGHT THERE.

look at this like a long cylinder ok... two circles and that big closed space in the middle. Total surface area is the surface area of those to cirlces and the big space thangy in the middle aight. you drill ah hole in that cinlinder, it will take surface area away from the two circles but adds a respective amount to it because it adds more of the big thingy in the middle. But total surface area is not what increases breaking ability....no it isn't, you know why, becuase the break pad will not even so much as touch the inside of that hole, unles it's a sponge or you have a 2 ton clamp or osmethign on it IT AIN"T GONNA HAPPEN. so takeing that into consideration (and contradicting short and blunt), the only surface that really matters, is one of those circles of the cylinder, becuase that's what the pad is going to touch, and by putting a hole in it (not too mention the billions you'll see on a 911) you're takeing away the surface area that the pad will acutally touch...you know what we call that surface area...CONTACT area. and tHAT is the surface area taht matters, the surface which is acutally in contact with the pad, the contact (surface) area.

and i can only hope that i didn't jump the gun again with that one like i did the last thread i made lol

oh and 911, porsche would most DEFINITELY put it on there jsut for looks if they can still compensate with some performance, which is (as one of the wiser ones in this thread once said) why the discs are 14". Also, the bose sound system and memory seats were mentioned, another fnie example of spareing no expense on the performance on the car...mm hmm indeed..there is a reason why it's called EXOTIC.

oh and reason why lots of these companies may still put x-drilled rotors, is maybe becuase the newer technology hasn't fully proven it's self, can't really see why that's so unthinkable. x-drilled rotors has been around for 50+ years, so why shoudl peopel suddenly change to a new form of rotor, the same thing was talked about in an older post about the wireless throttle body in the '05 mustangs. so there ya go, have fun with that, and even though you thought about it, don't htink TOO deeply about it, or else you'll shootin yourself in the foot (which i tend to do often, so correct anythign i may have wrong)

thank you and have a good day
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Old 04-14-2005, 11:43 PM   #126
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Re: Re: Cross drilled rotors, better or not?

Quote:
Originally Posted by breaknstuf4fun
ok, now i'm posting this for two reasons

one: i haven't been on in a little while and i like getting attention lol

but Two (and most important): i think som ething here needs to be just bluntly put in stead of putting math formulas here!

i mean really, skyline, silver, and moppie, had everything finally sorted out and then holes and surface area had to be thrown in again.

let's make this short and blunt eh?

YES, the holes will add surface area, but what KIND of sruface area, THAT'S THE KICKER RIGHT THERE.

look at this like a long cylinder ok... two circles and that big closed space in the middle. Total surface area is the surface area of those to cirlces and the big space thangy in the middle aight. you drill ah hole in that cinlinder, it will take surface area away from the two circles but adds a respective amount to it because it adds more of the big thingy in the middle. But total surface area is not what increases breaking ability....no it isn't, you know why, becuase the break pad will not even so much as touch the inside of that hole, unles it's a sponge or you have a 2 ton clamp or osmethign on it IT AIN"T GONNA HAPPEN. so takeing that into consideration (and contradicting short and blunt), the only surface that really matters, is one of those circles of the cylinder, becuase that's what the pad is going to touch, and by putting a hole in it (not too mention the billions you'll see on a 911) you're takeing away the surface area that the pad will acutally touch...you know what we call that surface area...CONTACT area. and tHAT is the surface area taht matters, the surface which is acutally in contact with the pad, the contact (surface) area.

Sorry to burst your bubble... but isn't that kind of common sense? Not only are you reviving an old thread, but you're also not giving any new information that is helpful...

The fact that it does infact add surface area is important, because what the people on top were trying to say is that the extra surface area does help cooling.. however, since there is less contact area, more heat is generated, so in the end, its all useless... not to mention, it also makes the rotor physically weaker..
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Old 04-15-2005, 02:09 AM   #127
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Reviving old threads is poopy. Please don't or I have to close them
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