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Drilled and slotted rotors

dpAtlanta

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Please do show me the physics that explains how less surface area has more grip
An interesting side note... if friction has nothing to due with area, why are race car tires so wide?
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luc

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Yeah, I do.
Drilled rotors from factory on viper, ferrari and both porsches. Boxster Spyder is sitting outside.
What would the engineers at the OEMs know about drilled rotors? Hmm.
Only cars that don't have drilled rotors are my mustang and audi.
I prefer non drilled rotors by the way.


IMG_7566.jpeg
They know that they look good and people buy those type of cars as much as a fashion statement than anything else
 
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Cobra Jet

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Not all drilled rotors are equal either from a manufacturing standpoint.

Keep checking the rotors drilled holes for any outward cracks coming from the drilled hole. Inferior products with drilled holes will succumb to severe cracks usually emanating from the edges of the drilled holes outward on the rotor surface. With such cracks comes further deterioration of the rotor due to expansion/contraction of the crack and rusting within the crack which can degrade (over time) the rotors integrity.

Not saying all drilled rotors are an issue, but being in the hobby as long as I have and belonging to many automotive forums aside from Mustangs - it is a very common issue with inferior products or “cheapER” products bought because all the other Sheeple bought them too…
 

Jstang23

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Yeah, I do.
Drilled rotors from factory on viper, ferrari and both porsches. Boxster Spyder is sitting outside.
What would the engineers at the OEMs know about drilled rotors? Hmm.
Only cars that don't have drilled rotors are my mustang and audi.
I prefer non drilled rotors by the way.


IMG_7566.jpeg
I should clarify, Iron rotors with drilled holes are where the problems start. Carbon ceramic rotors with holes are fine because they aren’t drilled. When you drill a piece of metal you actually develop very small cracks, similar to how a piece of wood sometimes cracks when drilling. Most of the OEMs follow this standard by ”forging” the iron rotors with the holes so the metal goes through the heat curing process with the holes there. But most if not all of the aftermarket parts actually use a drill. When you subject your car to the track the heat produced will develop cracks around these holes, eventually even with the forged type. Please understand this is not an opinion it is a proven fact that I as an automotive engineer have had to work with. Rotors like brake pads are wearables anyways, so you’ll replace them either way. The opinion comes into play that I don’t recommend tracking with drilled rotors. You will develop cracks around the hole, just depends on how fast your driving.
 
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5.0Vonn

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I did the Powerstop kit, Z26 I think it is?
Anyway, every bit as good as stock, far less brake dust. 100% satisfied.
Spirited driving, no track work.
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Your setup looks sick !
 

GrayMater22

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Depends on what you're using it for but generally there will be no difference or worse performance. If you are using it for the street then you won't notice a difference. If you use it for the track then you'll find you get worse performance. Yes they may cool better (depends on ducting and airflow to the rotors) but you're losing surface area. So your pad bite will have less surface area and lose some of its stopping power. In addition, you'll find that when they reach their maximum rated temperature they will develop cracks around the drilled holes, this will eventually ruin your rotors. My advice to anyone tracking their car is to stick to blank rotors or slotted rotors. The drilled rotors you see on racecars replace their rotors after every race and are generally not drilled but forged with the holes. Drilled are mainly for looks, and they do look very good! :like:
Exactly, not to mention I have been to scca events that do NOT allow drilled rotors on the track and it is due potential cracking.
 
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ShadesOfBloo

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An interesting side note... if friction has nothing to due with area, why are race car tires so wide?
Because tires have properties besides friction that affect their job.
Sticky tires also have the property of adhesion, and that does vary with surface area.
Also, big tires with a big contact patch spread out stress and heat better, and last longer.
 

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Jstang23

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I wasn't... friction is not related to area, but even some engineers have a hard time answering the question.
Yes you're right but there are a lot of there properties that effect braking performance that do have to do with surface area that you are neglecting. Engineering ain't that simple bud.
 

ShadesOfBloo

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I just changed my rotors to Drilled and slotted rotors, I’m curious to see if there’s much of a difference in cooling/braking power. Any thoughts?
My thought is that I haven't heard of a car in Formula 1, NASCAR, or any endurance racing series use rotors with holes or slots in them. Not in my lifetime.

They might make your car stop harder on the street.
It's more likely the cheese grater brakes will wear down your pads much faster than the factory rotors.
 

Jstang23

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I've been doing it for 34 years...!
Then I’m surprised you don’t know that braking performance and clamping force deal with area quite heavily.
 

dpAtlanta

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The question was: "... if friction has nothing to due with area, why are race car tires so wide?"

I am not talking about braking, just the relation between friction and area. Area is not in the mathematical formula for friction.
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