WHY Blank rotors are better than cross drilled and/or slotted

HKS-GT2835R

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While looking up some information for my car on the HT forum I found a great thread which you guys might find useful.
<<I'm posting this here too as well as the Tech. Misc. Forum because this really affects people in here the most and I care about your safety because I have seen too many people get hurt by negatively affecting their car via modification and I feel braking is a VERY important system for this.>>http://honda-tech.com/zerothread?id=1437507

Ok I'm hearing a lot of conjecture, and people are STILL blowing money on ****ty rotors, so I will tell you all why blank rotors are better.

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 also used, and we dont use that either.

The other reason is so called heat dissapation. I don't have my physics and thermo books with me, but the logic 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.


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 **** 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.

Here is the link to the thread: http://www.honda-tech.com/zerothread?id=1437513

what do you say guys?
 

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Well, if slotted or cross drilled disc is not better than blank ones. Why would big companies like Brembo, AP Racing, AMG, EBC, StopTech, Grippen, TRD, Nismo, Wilwood..etc want to produce this kind of brake system upgrade? :hmmmm: I think they did take their products and put them into a series of heat test before they sell to customers. As we all know that a set of brake kits from these companies is not cheap they cost almost thousands. If its just for looks why its so expensive ?

I do saw a lots of cross drilled disc used in racing. I'm making the above statement on my own opinion and observation. Didnt meant to pick on anyone and no hard feelings. :smile:
 

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hhhmm... interesting discussion. however i have no input on this. i hope others with more knowledge on this can help on this issue.

errrmm... anyone noticed if the F1 cars are using 'blanks' or 'crossdrilled & slotted'? probably it would be a good indication there since they are mainly looking for better performance instead of cosmetics aspects of the sport...
 

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if black blank rotor..i believe it will be very very good ler
 

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crossdrilled good because the water on the disc can be dispersed away mah... like how the bunga on tyres work in wet...

that is why some say non-crossdrilled or slotted disc is good... they work same like slick tyres,.... more grip... but works best on hot weather...
 

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TitanRev said:
I do saw a lots of cross drilled disc used in racing. I'm making the above statement on my own opinion and observation. Didnt meant to pick on anyone and no hard feelings. :smile:
none taken (which how it shud be).
opinions man..wanna get lotsa opinions so that we know what is and what's not.:cool:
yes, braking upgrades do cost both balls, and it is worth it..but IMO even if its just for looks it will STILL be expensive.:biggrin:
ross drilled AND slotted is overkill but it looks impressive.

here's the deal ya..you can and shud use plain OEM rotors if you aren't doin' any performance driving (competition).

You can get slotted alone or cross drilled alone but for your driving needs those are overkill too.

the slots or crossdrill holes "outgas" the heated gas built up in between the pad and the rotor when you drive aggressively and are on the brakes under a lot of heavy braking like in a lapping session or drifting (?).

You don't build up the gases and you don't go to those high brake temps in street driving.

BTW braking distance in terms of rotors is determined by the size (diameter of the rotor) or surface area provided by the rotor and the clamping force of the caliper (number of pistons). The slots and crossdrills prevent brake fade...they aren't directly related to stopping distances per se. If the temps and outgas build up get too high from repeated hard braking over many laps, then stopping distances and brake lock up is affected. That's when the slots and drills are important.

Be careful about advertised crossdrilled Brembos. Some shops get the OEM Brembo replacements and then drill them and sell them as "crossdrilled Brembos". The real crossdrilled Brembo rotors have the holes created from a mold...there's no actual drilling involved. Drilling creates more stress risers in the rotor and makes it easier for cracks to form at the holes over time since the structure of the hole is weakened.

Yes Brembo is one of the best rotors around but if the diameter is the same and you don't need the outgassing performance, why bother pouring your money into it?

SkYwAlKeR said:
crossdrilled good because the water on the disc can be dispersed away mah... like how the bunga on tyres work in wet...
...
i've read somewhere that it actually hurts wet-weather braking. them journos got this hi-speed photograph of it and it shows that water gets in them holes/grooves, which increases slippage. and IIRC those holes/slots are for brakedust?

keep it comin' & keep it clean, guys. this is great stuff
 
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sam1741

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well when i lean physic..
the law said : the larger the contact area, the more friction generated

i think this means blank disc are better

but i think the 'holes' are for rainy days...
like..anyone ride bikes before knows.. when rainy days your disc brake wont 'eat'.. cause one later of water on it.. so here where's the holes comes to work...
(dono how to explain anyone can help me out?)

just like why long long time ago F1 tyre is black rubber one with thread or any pattern, (larger contact area), but during rainy days they will use tyres with lines (to channel the watter away.. raining days there is one layer of water on the road)
 

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i do not agree with sam's opinion as i was riding a motorbike before, full disc...and the braking was not too good when it was wet. even both my disc was cross drilled, the bike was not braking too good when it was wet and cold, but once apply some hard pressure on the brakes and the disc heats up,the braking improves ;) so erm, beware when you are riding fast and your brakes are not working, just apply light preesure till the disc heats up then the braking will improve :D

will elaborate more when im home :D
 
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gavan said:
i do not agree with sam's opinion as i was riding a motorbike before, full disc...and the braking was not too good when it was wet. even both my disc was cross drilled, the bike was not braking too good when it was wet and cold, but once apply some hard pressure on the brakes and the disc heats up,the braking improves ;) so erm, beware when you are riding fast and your brakes are not working, just apply light preesure till the disc heats up then the braking will improve :D

will elaborate more when im home :D
agreed..my bike got cross drilled double disc up front, and it sucks when wet.
when heated up properly, say..2~3 minute of riding, then it'll be a BIT better.
my guess it's due to stainless steel discs. cast iron rotors are better in wet.
 

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HKS-GT2835R,
Great post for knowledge sharing.

I was contemplating of getting either slotted only or crossed drilled and slotted rotors, but this post really got me thinking hard!!! Looks like cross drilled and/or slotted rotors aren't a necessity for me now...

BTW, one team that entered the MEM race this year used crossed drilled and slotted rotors throughout the race. There was some cracking in the disks after the race ended. Not sure if it was due to the race being dry at the beginning and ending up wet at the end...
 

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zamnov, my 0.02, go fer braided brake line & hi-performance brake upgrade man..
 

SkYwAlKeR

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i've read somewhere that it actually hurts wet-weather braking. them journos got this hi-speed photograph of it and it shows that water gets in them holes/grooves, which increases slippage. and IIRC those holes/slots are for brakedust? keep it comin' & keep it clean, guys. this is great stuff
i thought if water is guided away from the disc, hyproplannning would not occur when ur brake pads come in contact with ur disc??... thats why they have slotted and crossdrilled disc..

besides, dont crossdrilled and slotted disc cools off faster compare to normal ones??...
 

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SkYwAlKeR said:
i thought if water is guided away from the disc, hyproplannning would not occur when ur brake pads come in contact with ur disc??... thats why they have slotted and crossdrilled disc..
well, i read that somewhere..that's why i'm here to know whether it's crap or truth..:tongue:
i still believe them holes n grooves hurt wet weather brakin'..but i might be wrong!:biggrin:

SkYwAlKeR said:
besides, dont crossdrilled and slotted disc cools off faster compare to normal ones??...
IMO because they heat faster too..

urm, since there's less metal on the drilled/slotted discs, that means lower maximum potential heat holding ability. youre taking metal out of the rotor when they are drilled, true?

this is an extreme and not exactly scientific example but, lets say you have a 16" rotor, it holds a lot of heat, it takes a lot of braking to max out its holding ability and then turns red.

well if you drill/slot that rotor it might only have the same amount of metal, say..as an undrilled 15" rotor? which if you gave the same beating to would be glowing red a lot quicker, because it doesn't hold as much heat.that's why i say they heat faster too.
IMO this cold-hot-cold lifecycle will shorten out OEM discs life, if they're slotted/drilled, yes?
 

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here's a race dodge viper on blank disc..
note the small slots on the discs, which i think acts as thickness level indicator to the discs




plz excuse the size..
heres another interesting shot...
porsche gt3 cup car, front brakes.
small slots. hmmmm:bath:



BAR F1 brake discs for interest sake:


for racing, well..bigger is better, as ppl wud say..:tee:
 

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f1 they using ceramic disc...i dun think they can drill holes n make slots on tat.....somemore ceramic can withstand high temperature and dun heat up as easily as steel...
always i heard is get slotted disc is good enuf n drilled disc can easily cracked....
 

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In F1, I'd assume they put a huge amount of R&D into their pad compound so as to not produce gas and dust. Therefore, they can run a solid disc.

Personally, I think upgrading to steel braided brake lines, performance pads and good brake fluid is enough.
 

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i thought ceramic brakes has slotted and crossdrilled type one??.. coz i saw the brakes in ferrari/porsche in best motoring... their ceramic brakes also slotted...
 

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Eh..guys. This theory just struck me in the head when i was taking bath yesterday.
Anyone with my age or older than me would remember this. When i was a child, my grandmother or grandfather would teach me to poke holes in a bowl of rice to cool it down faster or make a hole in the center to cool the rice faster. I do think that this theory applies to the brake too.

2 steel block that has a same mass and dimension but 1 is drilled with holes which one would cool down faster ? the one with holes rite ?

Why ? because more heat can be transfer to the ambient air. Heat can be transfered from the surface to the air and heat inside the disc can be transfer to the holes and air thus provide better cooling. If only a blank rotor heat can be transfer to the ambient air too but heat transfer only happens on the dics surface heat inside the disc will have to wait the surface to cool down to transfer more heat to the surface.

there are 4 principles in heat transfer.
one of the principle is (Heat is ready to flow or pass to anyhing that has less heat.)

So what i think is the holes in the disc surface is to remove heat at a more faster rate because ambient air is definitely cooler than the temp created by the braking force.
If a brake temp is too high, brake fading will happen and it may cause the dics to bent due to the high temp. We know that metal is hard to bent when its cold but when its heated to a certain temp it could be bent much easy.

Another thing is with cross drilled or slotted, we can increase the working temp of the brake system. With faster heat dissipation rate we can get a better or higher working temp.

Just like why some cars install oil cooler. oil cooler will keep the oil cool so that you can rev much higher and the oil can sustain a more severe driving condition without overheating. If the engine temp is too high, efficiency will drop. Just like our brake, if its too hot it's efficiency will decrease too.

Just my own 0.0002 opinion only. No hard feeling guys.:biggrin:
 

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no argues...no problem with ori slotted or cross drilled...
not those u drill yourself for the sake of looks only...
 

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First and foremost, the rotors being compared has to be parrallel.

How on earth can one compare a full race composite compound blank rotor to a cross drilled and slotted street rotor?

It would be like testing the performance of a jet engine against a Columbia shuttle rocket engine.

A fair comparison of braking efficeincy would be a blank street rotor against a cross drilled and slotted street rotor.

In other words, compare apple with apple.
 

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Comparing $#!+ with Chocolate...

Braking under normal condition and braking under wet condition, how can I say, need to see the skill of the driver... Who would lock their brake when coming to a patch of water on the road?? And also when the disc brake is hot enough, the water will vapourized if kena water... I dunno much about technical stuff, so correct me if i'm wrong, but i still know physics...
 

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tk2005takeru said:
the water will vapourized if kena water... but i still know physics...
:biggrin: yes sir...you do know your physics.

Most track junkies prefer slotted/grooved/dimpled rotors.
However, the original writer (redline96lx) is very naive in his arguement. And apparently forgets basic common sense.

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.
Hot air raises genius. Moreover, when your rotor is spinning, air gets blown out throught the spinning vents. Even in grooved/dimpled rotors, air is not going to stay there to continue getting heated.

When stopped or moving, the pad transfers heat into the rotor because its made of cast iron.
Heat flows from areas of high temperature to areas of low temperature. There is no definite direction between the pad or disk. Disk are usually cooled better, and hence they usually take away heat from the pad. Have you seen cooling fins on brake callipers?

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.
Unless you plan to keep your hand in prolonged contact with either choice, 150degrees steam will "burn" your hand more. Heat transfer is much much faster. 150% metal can store more heat energy, that's all.
The original aim for slots/holes on brake disks are not to store heat, but instead to lose heat. I'd galdly trade off that small loss in thermal capacity for the increased heat dissipation.

Even Porsche and Ferrari will admit that the cross drilled rotors they use are for looks.
Link/proof please.

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.
They use brake cooling ducts because it lets them control brake cooling easilyby switching duct sizes. Moreover, F1 brakes need fairly high temperatures to operate, which in that case, only a solid rotor would be structuraly safe. (most of us wouldnt even reach those temperatures on a daily basis anyways.) 24hr leman cars use slotted/grooved disks, jgtc cars use them, alms cars use them, wrc cars use them.

then you have a better brake setup because you have OEM parts
Sure....I'll take my stoptechs, alcon, and brembo, prosche...you take your acura RL setup. Lets see if you can outbrake me.
 

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gavan said:
i do not agree with sam's opinion as i was riding a motorbike before, full disc...and the braking was not too good when it was wet. even both my disc was cross drilled, the bike was not braking too good when it was wet and cold, but once apply some hard pressure on the brakes and the disc heats up,the braking improves so erm, beware when you are riding fast and your brakes are not working, just apply light preesure till the disc heats up then the braking will improve



will elaborate more when im home
HKS-GT2835R said:
agreed..my bike got cross drilled double disc up front, and it sucks when wet.

when heated up properly, say..2~3 minute of riding, then it'll be a BIT better.

my guess it's due to stainless steel discs. cast iron rotors are better in wet.

hahaha
honestly.. my bike's disc also got holes
also suck when it wet... sometimes scares me only..

but i beleive the braking power 'come back' faster then blank disc...
i cannot proove lar.. cause i not ride with bike with blank disc before
but i have seen some older bike that is using blank disc
maybe i should borrow some to test someday.. :D :D
 

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brake performance decrease when raining because your tyres canot grip, nothing to do with brakes