slotted or blank

[Daveho1]

hey guys,
its been commonly accepted for ages that slotted or cross drilled rotors are superior to blanks because they force the gasses created from breaking out and are super heat sinks and are fans and are just better cause they cost more and Ferrari do it so must be good.
which for ages i thought that slotted was the way to go too but there seems to be a alot of talk about blank rotors being superior due to the added friction aria and that the slots are no longer needed for gassing out due to new brake pad compounds.
any one out there that knows there stuff wanna tell me whats real?

[Hondarally]

Here's an extract from a guy I know who is an Engineer working for a large brake manufacturing company (has been there over 10 years). I'll let you draw your own conclusions, but given the amount of time he has spent testing these things, I think he probably knows a bit more than the average brake salesman. NB I admit I ripped this quote from another website, but I know the source.


Aaah, the fabled "outgassing" that is so often talked about on Interweb forums (and the real-world gatherings of enthusiasts that predate them), but which has never been observed in the sheltered world of brake engineering.
I've had good pads and *****ty pads that have nearly burnt our dynos down because they get too flamy.

Actually, it's only relatively good pads that get that hot. *****ty ones tend to self-regulate. They get slippery at high temperature, which puts an effective limit on how hot they can get. Can't get any hotter if they're not absorbing any energy. W00t, we're back on the Papal Decrees of Thermodynamics thread.

Anywho... the conventional "wisdom" of slotted rotors is that they clean the decomposed friction material off the surface of the pad, so you have good fresh material ready to do the work. But the decomposition/combustion products that you get at the surface of friction materials are part of the material design.

Most modern materials - especially high-performance ones - are scorched in production (sat on a 600° plate for ~2 minutes) to get this surface chemistry started, rather than waiting for it to develop in use. Without a scorch layer, performance is shyte.

If your salami-slicer rotors scrape the scorch layer off, you're losing the good stuff.

All the testing I've done confirms that friction levels are lower, and less consistent, on slotted rotors. And the pad wear rate is just ridiculous.

One particular Australian OEM wanted to sell slotted rotors in their blingbling "genuine spares" shop, which meant they had to get them through ADR testing that requires equivalent brake performance to OE - no better, no worse (within 15%). Everybody assumed that would be no problem, because everybody knows that slots are just a cosmetic thing with no performance benefit. Turned out they failed the ADR brake test, because the fade friction went through the floor. So there are no slotted rotors in the blingbling department.

Of course, that's using normal road pads. But I've seen the same thing using higher performance pads too. Ones that will quite happily turn rotors translucent red and burn all the seals out of calipers until the brake fluid pours out to cool the pads down.

I'm always confused when I see slotted rotors being used by people who should know better than I do what the effect is. Wondering whether there's something that they know that I don't. I'm yet to see any evidence to suggest that they are used for anything other than cosmetic reasons.

[Daveho1]

thanks for the post :)

[dougie_504]

I was under the impression that blanks are better for braking and all you need is good pads for higher temps. Brake vents are optional to keep the temps down a little if you're serious about racing.

Rest is bling.

[Daveho1]

the more i read into it im inclined to agree, look at f1 cars not a slot or cross drill in sight.

[curtis265]

it's all bling

looks damn cool too haha

[bennjamin]

always used blanks. Cheaper - and should be considered a consumable anyway.

[EKVTIR-T]

porsche use crossdrill and theyre one of the most highly regarded braking on street cars so....

[Daveho1]

true but do the cross drills contribute to that or is it the ceramic compounds used, as previously stated F1 cars dont use slots or cross drills but they do use ceramic, like Porsche

[DreadAngel]

porsche use crossdrill and theyre one of the most highly regarded braking on street cars so....


true but do the cross drills contribute to that or is it the ceramic compounds used, as previously stated F1 cars dont use slots or cross drills but they do use ceramic, like Porsche

As above, check out Skyline BNR32 and Cross Drilled Disc to see what happened to them...

[mocchi]

As above, check out Skyline BNR32 and Cross Drilled Disc to see what happened to them...

what happened to them?

[Daveho1]

DA isnt into give us all the answers, we gotta earn the knowledge.
end of the day the consensus of people in the know seem to agree blank is superior, even if slotting or dross drilling makes a difference (hasnt been definitively proven) it dosnt justify the sometimes double or tripple price tag.
thanks guys.

[e240]

the more i read into it im inclined to agree, look at f1 cars not a slot or cross drill in sight.

Difference is that f1 brakes are carbon carbon...

[EKVTIR-T]

I assume Dread is talking about hairline cracks on the holes,maybe he can confirm?

http://s29.postimg.org/4kvtpwaiv/attachment_php_attachmentid_397640_d_1355351934.jp g




its interdasting though,majority of the big name brake makers use slots or crossdrill

Endless ProjectMu AP etc. etc. so makes you wonder is it marketing or based on r&d results


also I think the main goal is the pad staying within its heat range regardless of rotor design



since youre comparing F1 with honda civics,may as well throw in that nearly all sport bikes use drilled rotors too,even with such a thin disc :p

[Daveho1]

very true... hmm the more i read the more im inclined to belive it just bling though

[DreadAngel]

what happened to them?


DA isnt into give us all the answers, we gotta earn the knowledge.
end of the day the consensus of people in the know seem to agree blank is superior, even if slotting or dross drilling makes a difference (hasnt been definitively proven) it dosnt justify the sometimes double or tripple price tag.
thanks guys.

Lol not that, usually I have to run off do something else so drop a hint, other times can sit down and type out an answer hehehe :)

BUT yes you all gotta earn the knowledge... :p


I assume Dread is talking about hairline cracks on the holes,maybe he can confirm?

http://s29.postimg.org/4kvtpwaiv/attachment_php_attachmentid_397640_d_1355351934.jp g

its interdasting though,majority of the big name brake makers use slots or crossdrill

Endless ProjectMu AP etc. etc. so makes you wonder is it marketing or based on r&d results

also I think the main goal is the pad staying within its heat range regardless of rotor design

since youre comparing F1 with honda civics,may as well throw in that nearly all sport bikes use drilled rotors too,even with such a thin disc :p

Indeed I am! Hairline cracks that start from the holes as very very miniature cracks on the circumference of the hole then stretching across the diameter of the disc then kaput. Its not only Skyline GT-Rs that have this issue, numerous other manufacturers and aftermarket ones have this issue to varying degrees too. To check, just google your brand and cross drilled and cracking to see first if its a common theme, remember to check what conditions they're being used under too. Many people have the combination completely wrong [Underspec'd Disc + Highly Abrasive Pads = Dead Disc] so obviously ignore these ones. Also note the country they're used in, some countries that experience more varied/extreme temp changes to Australia may also have different issues.

Endless, Project Mu, AP, etc. From what I've seen have not had issues when matched up correctly [I've not googled this so don't take my word, only from my own projects and others I've worked on], perhaps a little of marketing, afterall many people [Myself included] love the looks of slots and or cross drilled. They do have disclaimers iirc regarding their use too :)

On a side note, more and more companies are using 'dimple' or a special form of dimple like Endless E-Slits [Which is a combination of Slots and Dimple]. These work in similar fashion as the cross drilled except without drilled all the way through so the disc's integrity remains more intact than being drilled :)

The way I usually select it:
NB - This selection is usually for mild to moderate applications without looking at BBKs, etc.

#1 - Application - Street, Street + Spirited, Semi-Race, Race, etc
#2 - Tyres - With so many cars with ABS/EBC/etc this is a little more obscure but if you're like me and usually don't run ABS then its quite important to match up your tyres and braking power. Locking up because brakes too powerful or inadequate braking technique isn't going to do you any good.
#3 - Pads - Next on the list is pads, this way I know what temperatures and μ the disc can expect.
#4 - Disc - Now I can select the disc, afterall the disc are there to withstand the temperatures and pressures so its best to leave them till last. Select the disc made from material right for your application [Cast to Aircraft Material/Ceramic/Carbon/etc] with the right treatment [Heat Treated, Zinc Coated, etc] and face type [Plain/Blank, Slotted, Cross Drilled, Dimpled, Combination].

I might be making a Tech writeup for brakes, but gotta finish suspension first XD