Brake Rotors: Slotted versus Cross-Drilled

[Silvia_Drift]

Hey guys. I just wanted to know the advantages and disadvantages of sloted rotors versus cross drilled rotors. So far all I know is that the drilled rotors crack easily and the slotted rotors use up brake pads quickely. Which type of rotor is better and why? Thanks.

[graywolf624]

Heres another version of my article on the subject.. all polished up:
http://www.mazda6tech.com/index.php?...d=19&Itemid=32

[oscargarza88]

and what about the ones that r very weird? like curvy, its not circular, do u know what im taking about?

[oldsnail]

Originally Posted by oscargarza88 and what about the ones that r very weird? like curvy, its not circular, do u know what im taking about?

slotted?
i have crossdrilled coz they look cooler to my eyes.

[oscargarza88]

Originally Posted by oldsnail Originally Posted by oscargarza88 and what about the ones that r very weird? like curvy, its not circular, do u know what im taking about? slotted? i have crossdrilled coz they look cooler to my eyes.

no no
look let me explain beter...
imagine some drilled rotors... and now instead of then beind circular like the normal ones thet have like a wavy ouside, like if u got a rotor, put it standing and hittind it each 2 inches and bending it (imagine it), so the ouside is like wavy, thats the only way i can explain!

[graywolf624]

"and now instead of then beind circular like the normal ones thet have like a wavy ouside, like if u got a rotor, put it standing and hittind it each 2 inches and bending it (imagine it), so the ouside is like wavy, thats the only way i can explain! "
You mean wave rotors?

Stay away from them like the plague.. We are fixing to see a bunch of lawsuits from them, they are an accident waiting to happen. Less metal on a street car rotor is generally not a good thing.

[SPAD]

I know wat u are talking about.I always wonderd about them. like u said less contact with the pad.they just look cool

[oscargarza88]

^^
i thought so, but i was curious casue if they make than it had to be for a reason, and i also saw a kart like mine with some of those, so i thought they were good or soemthing

[graywolf624]

thought so, but i was curious casue if they make than it had to be for a reason, and i also saw a kart like mine with some of those, so i thought they were good or soemthing

When you have something like a motorcycle or a go kart the weight of the vehicle is so light you need minimal heat shed ability. At that point you want to cut down on the mass of the rotor(both from a unsprung mass and from a inertia stand point) since you dont need extra heat capacity. In a street car the exact opposite becomes important. So I could see something like cross drilled or waverotor for a motorcycle because they dont have to deal with anywhere near a cars heat. Still have the structural problems of course.

That is part of porsches claim to why they can do cross drilled on a street car. They over braked the 911 for street applications(not racing) so on the street it wont overheat. In that way the loss in mass and the less pad contact(in terms of added wet braking) can be considered better for the regular people.

[Ziploc]

i thought cars which had ducts that blew air on the rotor from the side would have drilled rotors to help cool and bring some air through the rotor

[graywolf624]

i thought cars which had ducts that blew air on the rotor from the side would have drilled rotors to help cool and bring some air through the rotor

You do ducting to duct cold air around the brakes.. Nothing really to do with cross drilled rotors at all. Any one who races will duct around their brakes.



The idea of optimal rotors is first you sink the heat into the rotor(the more room to sinc the better since that act is faster then the next act). The next act is the heat disippates from the rotor to the air. The issue is that as I said above.. The sink happens many times faster then the dissipation. From a physics stand point the heat shedding ability of a cross drilled rotor will be outweighed by the loss in mass to sink the heat into. The veins of a rotor act as a centrifigul pump pulling air from the center of the rotors to the outside. Cross drilled rotors act (only in the case of a veined rotor, in the case of a sold rotor they flow no real air at all) as inlets for air passing through the pump. However, this slight gain is outweighed by the other things I mention in the article.

[graywolf624]

A little bit to back me up and help you guys along. The leaders in the brake design industry on cross drilled/slotted.

"From Baer Brake Systems
What are the benefits to Crossdrilling, Slotting, and Zinc-Washing my rotors?
In years past, crossdrilling and/or Slotting the rotor for racing purposes was beneficial by providing a way to expel the gasses created when the bonding agents employed to manufacture the pads began to break down at extreme temperatures. This condition is often referred to as “green pad fade” or “outgassing”. When it does occur, the driver still has a good firm brake pedal, but simply little or no friction. Since this normally happens only at temperatures witnessed in racing, this can be very exciting!

However, with today’s race pad technology, ‘outgassing’ is no longer much of a concern. When shopping for races pads, or even ultra-high performance road pads, look for the phrases, “dynamic surface treatment”, “race ready”, and/or, “pre-burnished”. When these or similar statements are made by the pad manufacturer, the pad in question will likely have little or no problem with ‘outgassing’. Ironically more pedestrian pads used on most streetcars will still exhibit ‘outgassing’, but only when used at temperatures normally only encountered on the racetrack.

Although crossdrilling and/or slotting will provide a welcome path to expend any gasses when and if they develop, it is primarily a visual enhancement behind today’s often wide-open wheel designs.

Crossdrilling offers the greatest gas relief pathway, but creates potential “stress risers” from which cracks can occur. Baer’s rotors are cast with crossdrilling in mind, from the material specified, to curved vanes, behind which the holes are placed to minimize potential crack migration. Slotted surfaces are what Baer recommends for track only use. Slotted only rotors are offered as an option for any of Baer’s offerings."

"From Wilwood
Q: Why are some rotors drilled or slotted?
A: Rotors are drilled to reduce rotating weight, an issue near and dear to racers searching for ways to minimize unsprung weight. Drilling diminishes a rotor's durability and cooling capacity.

Slots or grooves in rotor faces are partly a carryover from the days of asbestos pads. Asbestos and other organic pads were prone to "glazing" and the slots tended to help "scrape or de-glaze" them. Drilling and slotting rotors has become popular in street applications for their pure aesthetic value. Wilwood has a large selection of drilled and slotted rotors for a wide range of applications."

"From Brembo
Why use drilled or slotted discs?
Drilling or slotting discs aids the disc in several ways:
The edges of the slots or holes continuously clean and refresh the pad surface as well as providing increased brake "bite". Additionally, they prevent gasses from collecting between the pad and disc interface.
The disc is lightened, thereby decreasing its rotational inertia.
Improved ventilation increases the disc's ability to shed heat, resulting in cooler operating temperatures."

"From stop tech:
Discs that have been drilled through with a non-intersecting pattern of radial holes. The objects are to provide a number of paths to get rid of the boundary layer of out gassed volatiles and incandescent particles of friction material and to increase "bite" through the provision of many leading edges. The advent of carbon metallic friction materials with their increased temperatures and thermal shock characteristics ended the day of the drilled disc in professional racing. They are still seen (mainly as cosmetic items) on motorbikes and some road going sports cars. Typically in original equipment road car applications these holes are cast then finished machined to provide the best possible conditions by which to resist cracking in use. But they will crack eventually under the circumstances described in another section (see Cracking). Properly designed, drilled discs tend to operate cooler than non-drilled ventilated discs of the same design due the higher flow rates through the vents from the supplemental inlets and increased surface area in the hole. That's right, inlets. The flow is into the hole and out through the vent to the OD of the disc. If discs are to be drilled, the external edges of the holes must be chamfered (or, better yet, radiused) and should also be peened. "

[graywolf624]

Apparently Tire rack has finally decided to cover their own ass on this issue:

Slotted, drilled or dimpled rotors offered as OEM replacements should not be considered appropriate for high-speed track use. While grooved, drilled and slotted rotors offer an enhanced appearance and add some resistance to the boundary layer of gasses that can build up between the pad and rotor, they are not designed to withstand the extreme temperatures that are produced on the racetrack. If they are used on the track, it is very important that the rotors be carefully inspected and should not be driven on if even minor signs of deterioration are seen. Note, too, that if these products are used on the track they are not warrantable.

http://www.tirerack.com/brakes/tech/....jsp?techid=87

[RC45]

I have answered all concerns about brake upgrades on my car, by "upgrading" every 6000 miles or so or when stress fractures appear - to solid (heat vaned) OEM replacement rotors at $30 a piece...

Retains my 60-0 in 100 odd foot braking ability - and costs less than night at a strip club to redo the brakes front and rear pads included..

Sure, my car doesn't get the the "OOooohsss..." and " AAAhhhssss..." at drives and meets... (until we start it up ) - but then again I don't mind beating on my cars brakes as intead of a $2500 to $3000 Baer etc brake replacement cost, I face maybe $240 including shipping for all 4 wheels