okay the other link was broken so I didnt get to see the flaming, but the last post said crossdrilling was for asthetics. In that case it looks like slotted dimpled is the way to go or should I just go slotted.
I would love some slotted rotors for my brake upgrade, but I used the spindles off a 78 Cougar and to my knowlege no one makes slotted rotors for such an appliction. Parts interchangabllity anyone? What other rotors from what other cars can I use on my 78 cougar spindles? Them maybe I can find some slotted for me???
slotted,and the dimple option seems ok but ill never buy another drilled rotor,my experiance was with a set of new cross drilled rotors on a 300zx afew years back,the things cost a fortune and by the time i had to take the car for its third wof[must get a warrant of fitness every 6 months]all four rotors were cracked,small cracks starting where they had been drilled.
ill go with slotted and dimpled rotors when i have to buy rotors again
The rotor acts as a heat sink. The kinetic energy of
vehicular motion is absorbed, converted to heat and
dissipated. Getting rid of mass in a calorific equation
like that is never a good thing. The small amount of
cooling from the holes is neligible compared to the
effective loss of mass in the heat sink.
Some Porsche vehicles have holes in their rotors-
it's mostly bling. What most people don't know is
the rotor speced for those applications was over-kill
to begin with, so even after the holes are factored in,
it's still an adequate design. Most rotors that people
drill do not have this kind of over-capacity from the
start. They are drilled in the mistaken notion that the
end result is an improvement. In most cases they are
"solution looking for a problem."
Akebono Brake Corporation
(supplier to Ford, GM, D-C, etc)
Farmington Hills MI &
I read alot about this for my disc brake conversion. Almost everything I read said that drilled rotors were not as good an option as smooth or slotted. Also read alot about the slots and holes being used to dissipate gases and having no effect on cooling the rotor.
"As this picture illustrates, cross drilling can cause severe stress fractures, shortening the life of the rotor and possibly leading to an unsafe situation."
I would say most aftermarket drilled rotors on a street car are a gimic. I think the material removed will only speed up brake pad wear and lead to cracks and warpage. From my experience aftermarket rotors are of questionable quality and material without holes in them. Unless you just want the look, there is no need for holes,slots,grooves,dimples or whatever unless you are driving your car hard enough to experience brake fade or overheating. If you do drive your car this hard cost should not be an issue and there are plenty of quality aftermarket brake suppliers. Race cars have dedicated ducting and sometimes fans to keep there brakes cool and get more frequent inspection and repair than the average street car. I guess what it comes down to is how long you want your brakes to last and at what cost. Good luck with whatever you decide.
In all seriousness, I don't have to prove that cross-drilled rotors are a bad idea for a street car. There is enough evidence on the web for that purpose.
Secondly - most cross drilled rotors are made such after they are cast - in otherwords, holes are physically drilled in a solid rotor after casting has taken place. Because of this, the grain structure of the metal is interrupted at the placement of the hole. This allows cracks for for along the grain structure of the metal.
If these holes are cast in the rotor from the beginning, the grain structure of the steel will form around the hole, not leaving unsupported crystals in the metallic lattice. These technically aren't drilled, but they are ventilated rotors. They are the best design for "drilled" rotors.
Also, drilled rotors on the top dollar race cars see extreme (!) pad temperatures, necessitating the ventilation due to pad off-gassing. Like SCode said, these rotors are regularly inspected and replaced as often as the engines are in these cars. There's no such thing as a 40,000 mile tuneup in racing.
On the street, you will see absolutely no benefit. The reason for the holes/slots is not for cooling, in fact the removal of metal makes conducting heat away more difficult. It is to allow the superheated friction material, which is now a gas, to ventilate from the rotors - this gas can actually build enough pressure to hold the pads off of the rotor if there is no or inadequate ventilation.
On street cars, on the odd chance you are on the brakes heavily for a long time, fade is prevented on most brake systems by slotting the actual friction material of the brake pad itself - a radial slot in the middle of the pad allows for gas expansion. In fact, you can add to this by cutting an additional groove along the width of the pad - giving it more area to escape. Again, if you see pad temperatures high enough to necessitate more than that, there is something seriously wrong. In fact if you see pad temps like that, you probably need to take your left foot off of the brake pedal.
If you are going to do extensive road racing or autocross, where brake fade (due to high pad temps) will be encountered due to speeds and techniques such as trail braking, you might invest in a set of slotted or properly manufactured "drilled" ventilated rotors, for the reasons mentioned above.