RedDjinn
Brake Rotors Slotted or Drilled which way do you swing?
Interesting read...
After i have gone out and bought new rotors i found this write up.
this is teh link Blank rotors are better than cross drilled and/or slotted - Honda-Tech
There is a lot of conjecture, and even more marketing influence saying that cross-drilled and slotted rotors are an "upgrade". This is not necessarily true, and in most cases, is just more expensive and can actually HURT braking performance. This is a thread to debate which rotors are best, cross drilled, slotted, both, or blank. I believe blank rotors are better, and here is why.
The reason for the creation of cross drilled rotors initially was to remove the "gasses" from the brake pads. HOWEVER, most of your modern brake pads (Axxis metal, AEM semi-ceramic) do NOT produce gasses when heating. This was on bad brake pads used in the 1950s and 1960s. Back then, asbestos was used as a bonding agent, but due to the health concern of asbestos, we don't use it anymore..
The other reason is so called heat dissapation. I don't have my physics and thermo books with me, but the theory is that the holes in the rotor are suppose to allow the brake pad to cool. So...air gets into the rotor from the inside of the vents. If you have a back rotor which is solid, air gets into these holes how? If your stopped, you are leaving air inside these holes sandwiched between the pads, thus creating air with a rising temperature. Its increasing in pressure from the heat, which I guess you "could" call a gas that would affect braking. So the cross drilled rotors do not remove any gasses formed by brake pads (because there are none created anymore) but could possibly inhibit the creation of "hot spots".
Cross drilled rotors have LESS contact area because of the holes.
But if the rotor is cooler, its better, right? Well no, because these rotors are not cooler. THe heat is generated from the pad/rotor contact. What removes heat the most effectively? When stopped or moving, the pad transfers heat into the rotor because its made of cast iron. the rotor has a lot of surface area and even vanes in it. But the little holes allow air in this surface contact, and you can transfer more heat into a solid big ass chunk of cast iron more than you can into the air. Don't believe me? Touch some steam at 150 degrees, then touch a piece of hot metal which is at 150 degrees. Which burns your hand? the metal. So let the heat transfer into the metal, because since it has so much more surface area, dissapates better.
Safety!!
Cross drilled rotors can crack! I have seen them!!
Even racing teams will reccomend AGAINST cross drilled rotors:
http://www.livermoreperformanc....html
Companies that sell cross drilled rotors that are redrilled may not be structurally sound. I have actually seen pictures of rear Integra rotors that have had hairline cracks turn into the rotor actually breaking apart!
Do your homework. Even Porsche and Ferrari will admit that the cross drilled rotors they use are for looks. So if you are one of those kids who thinks the little holes look cool, get a name brand drilled rotor like Ferrari does. The REASON Ferrari's 'holed' rotors are alright to use is because they are CAST with the holes in them, so they are not actually drilled into cast iron rotors. Cheap drilled rotors are not safe, and even the good ones are not necessary. Why do Ferrari do it? People THINK they want it, and it sells. If you don't believe me, go into the business world. You will learn that pretty soon, you can sell utter shit if people THINK its better.
Information I gathered from http://www.pdm-racing.com/prod....html
says:
"KVR Crossdrilled Rotors
Why should you upgrade to cross drilled rotors?
Simply stated, the function of any vehicles brake system is to stop the vehicle. This is accomplished by absorbing the kinetic energy stored in the moving vehicle, and converting it into heat. The friction caused by the brake pad rubbing on the rotor is the source of this heat. The more quickly and efficiently that heat can be absorbed and dissipated, the more quickly and efficiently the car will stop.
There are several contributing factors to this heat reduction. One of the most common sources of heat is from the gases produced by the bonding agents of the brake pad burning off. Under severe braking, this can actually produce a boundary layer of gas that pushes the pad away from the rotor, which can lead to excessive brake fade. The cross-drilled holes or slots in a rotor provide an escape path for these gasses (de-gassing or out-gassing are common terms), and allow the pad to stay in contact with the rotor. As well as de-gassing, cross drilling or slotting will provide better wet weather braking as water is swept through the holes, or down the slots.
A vented rotor can be viewed as an air fan. When in motion, the vents draw air from the center of the rotor outward. This air flow, over an increased internal surface area, effectively dissipates rotor heat. Cross drilling adds to this air flow, as well as providing additional rotor surface cooling. "
This company is just telling you that the rotors may be cooler, however they fail to mention that the holes really do create a more than substantial decrease in surface area, thus less braking, thus less heat created, thus the less heat CREATED will leave the rotors cooler, the holes barely do anything! Its the less braking lowering the temperature!
Slotted rotors-
Find me a company that uses stock slotted rotors. They remove brake dust, but if you study braking systems, you find that with modern cars, flat blank rotors and semi-ceramic pads, the brake dust causing the rotor to slip on it is almost non-existent. But the brake dust doesnt need all those lines. Notice how most front brake pads (and most back) have that line down the middle to give essentially two bite points. If OEM or racing companies found it to be a benefit, they would do it.
PROOF OF IT ALL:
Find me an F1 car as of now that uses cross drilled or slotted rotors.
They all use full ceramic rotors and ceramic pads. Are they drilled or slotted? No.
If they helped the fastest cars in the world, wouldn't they use them? Its basic calculations that show the lack in surface area does not make up for the possible loss in temperarure. They use brake cooling air ducts insted.
BIG BRAKE KITS:
Some have asked if the big brake kits are worth it. This is sort of a relative question, but the simple answer is no. Regarding the big ones with drilled rotors, if you know that they are cast that way, at least they wont crack. I will still advice against them.
In terms of a big brake kit, I have seen some for Civic DX models. Civics have the small pad, small caliper, and a 9.5" rotor. The big rotors are 12" in diameter, ok so the overall diameter is close to that of an Acura RL (1999). But the sweeping area (the area that the pad can grab) is still the same if they use the same caliper and same pad. If you have the same pad and caliper, you are using the same rotor surface, just farther out, so it will increase braking from stock. However, if you were to change knuckles, etc, and get Acura RL caliper (larger piston than your civic DX piston), RL pads (much bigger and taller), and RL rotors 11.8" but much more surface area is touched, then you have a better brake setup because you have OEM parts, and a better grip on more area of the rotor. The downfall is added weight (since big brake kits are usually 2 piece and lighter) but the benefit is that you have so much more stopping. Ok, so the big brake kit will have less unsprung and rotational mass (so a little better accelleration but less braking), but they tend to run over a grand, and you can use OEM parts to build a better setup for half that.
IN CONCLUSION:
Don't buy slotted or cross drilled rotors, blank are better, and stop better. Physics people, get me my formulas and help me out here.
If you must get rotors with designs on them, get the slotted ones by a good company, and DON'T get blank rotors redrilled with little holes all over them. IF you absolutly must have the rotors with holes cause you like em, get them from a company that casts the rotors like that. I have seen rotors break and this is for your safety!
HOWEVER, there is one sure fire way to get better rotors. Vented rotors, which we all have in the front of our car and cars like the NSX and new RL even have in the back, have straight lines for vents. This increases surface area to dissapate heat. If you go with "curved vane rotors", these will help, as they draw air from the hub area and vent it out the edges of the rotor. These rotors have no downfall, are directional, and will cost more than the non-directional regular vented disc rotors. The vanes are to point away from the rotation of the car, not toward it, as they draw air in to out, not biting into it and pulling it inward. Cooling ducts help by forcing cool air into the hub area to be vented out the curved vanes. Curved vanes usually start being effective at 50-60mph and above.
REMEMBER......
Your car will only stop as fast as your tires will allow. All the braking in the world wont work if your tires are bald and on ice!!
What have you bought and whats your impressions. Most of us buy pads and rotors at the same time. Who has the same pads with standard rotors and than put aftermarket rotors on? results your opinion?....
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Originally Posted by luke 3mps
