Slotted/drilled myth?

Matt90GT said:

This is what conflicts with your previous statement:

"They wont crack"

Proof is in the picture there. And that is a name brand unit = Powerslot

As the Baer FAQ states, there is no performance reason. It is all for LOOKS. The reason the factory supercars have them is to lessen the weight of the rotors. Even with the cobra 13" rotors, the drilling can lessen up to 1lb of weight off the Brembo designed units. That is 1 lb of unsprung weight off the car.

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I think what rydeon was trying to say is that under normal driving conditons they should be less likely to crack then under harsh conditions.

In reference to the quote from Baer brakes about slotted rotors having no purpose other than visual. That's crap. I understand that they are BAER and that I should be on my unworthy knees kissing their rings for even answering a phone call from someone as lowly as the likes of me HOWEVER.... As posted earlier... with the Taurus I'd gone through 3 sets of rotor in roughly a year and a half. Two of the replacements were done by Ford and the last by me (tired of the doing the run around through the dealership). Something with the front of that car was eating (warping) rotors. Enter ProStop slotted rotors. Problem all gone. This isn't one of those "My Buddy Told Me Stories". This is first hand. Again, I do give credit for the rotors probably being MADE better than the OEM piece but even given that... the rotor is still the same size and would still have to be able to dissipate the same amount of heat through a fixed surface area.

Daggar said:

In reference to the quote from Baer brakes about slotted rotors having no purpose other than visual. That's crap.

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Either its crap or they are hypocrits. Because both Baer and Brembo sell slotted AND cross drilled rotors for almost every application they cover. (even mustangs).

Expelling heat quicker may be subjective, but things slotted/drilled rotors dont do can proven by one simple equation: F=mu*Normal force
The only way to increase stopping power is to increase either the mu or the N. The mu is a result of the contact between the rotor and pad, so the only way to affect this is either by changing what the pad or rotor is made of. The N is the normal force applied to the rotor, thus it comes from your caliper. The only way to change this is through changing the faorce put out by the caliper, ie adding extra pistons, larger pistons, etc.

The only thing slotted/drillied rotors due is decrease the surface area....all this will do is put more psi on the pad in certain areas.....chewing up your pads, making you have to change them more frequently. You can't create extra force by reducing area....the force is only going to be as great as whats put into the system by the caliper.

93 teal terror said:

Expelling heat quicker may be subjective, but things slotted/drilled rotors dont do can proven by one simple equation: F=mu*Normal force
The only way to increase stopping power is to increase either the mu or the N. The mu is a result of the contact between the rotor and pad, so the only way to affect this is either by changing what the pad or rotor is made of. The N is the normal force applied to the rotor, thus it comes from your caliper. The only way to change this is through changing the faorce put out by the caliper, ie adding extra pistons, larger pistons, etc.

The only thing slotted/drillied rotors due is decrease the surface area....all this will do is put more psi on the pad in certain areas.....chewing up your pads, making you have to change them more frequently. You can't create extra force by reducing area....the force is only going to be as great as whats put into the system by the caliper.

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yes but mu is also affected by the heat generated. so if they do dissipate the heat better they will help braking power. thats why racing circuits use them. i have no experience with slotted rotors, but on the streets i would imagine that a good set of solid rotors will perform just as well.

Thats why I was saying heat disapation was subjective. But many people think they simply stop better b/c of less surface area....simply not true

93 teal terror said:

Thats why I was saying heat disapation was subjective. But many people think they simply stop better b/c of less surface area....simply not true

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agreed

We dont all buy them for the stopping power. I know well enough that they dont offer any brakin advantages in daily driving over plain jane rotors. I simply got them for the looks and the fact that my brake system had a habit of glazing the pads. The slotted rotors keep a fresh pad surface and prevent me from hearing the incessant squeeling. Not to mention i was able to get these slotted rotors cheaper than the plain ones from the auto parts storre or the dealer.

Companies are selling drilled rotors only because the market wants them (not the first time this has happened nor will it be the last). Drilling the rotor - even with chamfered holes - can lead to stress risers which lead to cracks. If you feel the need to provide a path for pad gases to escape use slots not holes. Most pads today have improved designs to the point that gases escaping under braking aren't significant enough to create the boundary layer that used to interfere with braking. A decently sized vented rotor and quality contemporary high performance pad is usually all that required to get the most out of your front tires - which actually do most of the car stopping.

By the way -- all the F=mu stuff regarding the pad/rotor interface applies to how the pads work on the rotor. But what stops the car is the F=mu interaction between the tire and the pavement. If the setup you have will hold the tire on it's friction limit for the full stop, bigger brakes/pads/better friction material won't stop you any sooner. They may allow repeatability without fade - but as a practical matter, that's only an issue on the road course.

Yeah...Mike's right. Vented/Slotted are ok but cross drilled rotors are prone to cracking....they look cool though. I guess that you could argue that cross drilling makes them lighter but so what- junk. That's why Powerslot sells so many rotors.

Michael Yount said:

By the way -- all the F=mu stuff regarding the pad/rotor interface applies to how the pads work on the rotor. But what stops the car is the F=mu interaction between the tire and the pavement. If the setup you have will hold the tire on it's friction limit for the full stop, bigger brakes/pads/better friction material won't stop you any sooner. They may allow repeatability without fade - but as a practical matter, that's only an issue on the road course.

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Hmmm.....I don't think thats correct. It all depends on the question of whether the tire stops the car or the brakes stop the car. I have no proof to back this up but im almost positive the rotor and pad lock up and as a result the tires lock up. Your saying the tires lock up and in return lock up the brakes. It would be extremely hard for the tires to lock up a system like the brakes. In a recent issue of MM&FF they replaced stock cobra 2 piston calipers and baer eradispeed rotors with 4 piston alcon calipers and slotted rotors. they decreased roughly 20 ft. at 100mph, 80mph, and 60mph. You could argue that the changing of brake fluid and new parts were attributed to the reduction, but 20ft is a pretty good reduction. It would be interesting to just change the fluid and see if it was the fluid or the calipers that did it. Basically I dont have any proof or knowledge to support this but i still think it makes more sense that the brakes lock up the tire, not the tire locks up the brakes

Some people are going to try and tell you that brake fade just doesn't exist anymore...

Found out for myself one day after a bit of a drive on a mountain road... "it was a 60's thing," my ass.

If I ever have to replace brake rotors, they are gonna be SLOTTED no matter how much hell anyone gives me for introducing stress risers. Not only do they vent gases but they are excellent for cleaning brakes -- I have seen lingings get ripped off from excessive debris buildup.

Drilled rotors on the other hand... that's just plain stupid.

Legendary said:

Couldn't have good brakes that work so well that you wouldn't have to lock up the tires? Then the tires wouldn't too much make a difference in braking. With my rear disc & 73mm front set up I can brake hard and not lock up at all. And it brakes alot better than when I had the stock brakes. That's without changing tires.

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That's correct.

When you're trying to slow the car... you're not trying to use whatever means of LOCKING the wheels. Otherwise why aren't we still using iron brake pads?

In other words, you want to maximize kinetic friction, not static. A brake setup is going to apply a certain amount of force, then any more and they grab. Better brake pad material will not be so grabby. Larger diameter rotors increase mechanical advantage, making it easier to keep braking torque at the threshold of kinetic friction. More pad surface also gives you more braking force before grab, though I don't quite understand it.

On the Baer site's FAQ pages this is addressed. They explain why some of their rotors are crossdrilled and others not. It depends upon the application and how the rotor was constructed. I believe Stainless Steel Brakes also has a FAQ page which will explain things better. It takes a little searching around, but good information is out there.

"Your saying the tires lock up and in return lock up the brakes." No, I'm not saying that, you're saying that.

Re-read the post guys. I said IF the current brake will hold the tire on the limit of adhesion (that's the definition of threshold braking - not lockup - it's the edge of being locked up), then a bigger brake won't stop you any shorter for the first stop. Now, if that same set up starts to fade on the second or third stop, then the bigger brakes help - they'll disapate more heat - pushing the fade limit out. Get 'em big enough, and you can go road racing with no fade for the whole race - depending on length of course. It's fact - there's no way around it. The tire stops the car - it's the only part of the car that's in contact with something that's not moving - the road. The brake stops the rotor - which is attached to the car. It's pretty elementary.

On the other hand, if your current brake WILL NOT hold your current tire on the limit of adhesion, or your current brakes are already fading on the first stop, then bigger brakes will stop you shorter.

From Car & Driver's big-brake test ---- "Our objective here was primarily to test brake fade, not stopping distances. Assuming a brake system is properly balanced, strong enough to lock a wheel, and not yet hot enough to fade, the stopping distance is largely a function of tire traction, not brakes. Think of it this way: All brake systems, stock and aftermarket, are able to activate the ABS, so how could a stronger brake shorten a stop? Eric Dahl, a brake engineer from Brembo, put it this way: "Don't expect the brake kits to stop you sooner, but expect the 20th lap to feel like the first."

Don't read stuff into it that's not there. No one is saying that bigger brakes won't help your car. What I'm saying is know your braking system before you start modifying it. If you have abs, and your car is capable of activating the abs for the whole stop, bigger brakes won't stop you shorter. In that case, stickier tires will stop you shorter - IF - big if - your brakes will hold the stickier tire on it's higher adhesion limit. Most of the foxes don't have abs -- but, see what you've got already before you changing things to be certain you're not gonna be disappointed with the result.

As for the other magazine's testing protocol - I read stuff all the time that amazes me. Current issues of MM&FF and 5.0 will still have references in articles about not using a cam bigger than "Y" lift to avoid p to v clearance. The fact is that many magazines out there have EXTREMELY weak technical staffs -- they are more about marketing and advertising than they are fact, and scientific testing. I've been reading them for lots of years, and there are a handful that really know what they're doing when it comes to testing things. You have to be really careful who you quote.

What your saying makes sense and like I said I have no proof or sources other than that MM&FF article. I know that the limit of adhesion is what we are talking about here. Obviously no one locks up the brakes when they do testing. However Im just wondering when the car DOES lock up.....which locks up which? The tires or the brakes?

The leg bone's connected to the hip bone -- rotor's connected to the hub's connected to the wheel's connected to the tire. The tire locks very shortly after the rotor does - due only to the flex in the tire's sidewall.

The other common misconception in cars like the fox body is the role the rear brakes play. There's so much weight on the front end to start with, and so much more shifts there under heavy braking that the front brakes probably do on the order of 80-90% of the stopping - the rears do little at all. For stock tires/suspension - replacing the rear drums with discs does virtually nothing to improve stopping power of the car. Mod the suspension to limit dive, or add more traction - and the variables change. The opposite of this is a car like the Porsche 911. With the engine in the back, and with a lot of anti-dive built into the suspension, the rear brakes do as much work as the front brakes do - which is one of the reasons that for years on both the track and the street, the 911 is consistently one of the best stopping cars there is, especially for the size tires on the car.