The discussion came up on EXD, I thought I would share my write-up here.

I have been telling people for years that getting SAME SIZED crossdrilled/slotted (or both) rotors reduces the surface of fricton of the rotor. The reason why the area of the rotor is important is because that's what braking is all about. Think about it. They make big brake kits for a reason, the bigger, the better.

Rough measurements (took an approx. guess with the provided picture of an ebay seller):

Slots VS Drilled holes
6x1/2"x1/32" VS 36x2/32"dia === that's roughly 3sq.in. -slots- VS 7.1 sq.in. -drilled holes- again these are just estimated values with reality in consideration. And if you get both that's 10.1sq.in. out of our stock sized rotors which have an approx 31.8sq.in. of area. Therefore you are reducing the area by roughly more than 32% with those holes and slots! (again, rough estimate!!!)

The F1 uses plain rotors on all their cars:



As far as "releasing gases". Here is a nice quote from the team-integra website that gives some food for thought:

Brake pads used to be made out of asbestos, which would give out gases when heated to extreme temperatures. These gases would get trapped between the pad and rotor and cause inefficient braking. Slotted and drilled rotors were designed to give the gases some place to go. Modern brake pads no longer out-gas after you have bedded them in.

Also, from wikipedia:

Although modern brake pads seldom suffer from outgassing problems, water residue may build up after a vehicle passes through a puddle and impede braking performance. For this reason, and for heat dissipation purposes, Cross Drilling is still used on some braking components, but is not favored for racing or other hard use as the holes are a source of stress cracks under severe conditions.

From what is gathered crossdrilling may only help in wet conditions?

Let's continue on...

Slotting is the preferred method in most racing environments to remove gas, water, and de-glaze brake pads. Some discs are both drilled and slotted. Slotted discs are generally not used on standard vehicles because they quickly wear down brake pads; however, this removal of material is beneficial to race vehicles since it keeps the pads soft and avoids vitrification of their surfaces.

Also::::

If you think about it. Let's pretend for a second your brake pads are special ones that expel gases. Where do the gases go? Inside of the rotor where the vented area is. The mere fact of having hot gases passing through there means that we have something impeding with the cooling element that is the vent on the middle of your rotor (this applies to the front only since the back disc aren't vented). This means that the rotor won't be properly cooled.

Now this would imply that one should choose between gas expelling and proper cooling: IMO proper cooling is what one should go for, because it's what makes your rotors not warp under heavy usage.

Also#2::::

Why do crossdrilled rotors crack? When you have a piece of metal with a hole in it, linear stress applied to the material has to go "around" the hole, going over other paths of linear stress, which causes a ''hot spot'' of stress which we call a concentration of constraints (unsure if that's the english word for it but it's a direct translation from french).


Cliff notes:

- Crossdrilling a same sized rotor reduces the surface of contact and might help in wetter conditions (BUT in the winter slush can freeze on the inside... 2loud2k2 had that problem).
- Slotting wears down the pads faster and are not really needed for daily driving, same thing applies for the surface of contact, however not as much as the drilled ones because the total area of slots is smaller than the one of the drilled holes.
- Plain discs are the best!



At last:

If you get a BBK with a BIG diameter difference with slots and/or drilled holes, the area has a chance to still be bigger than stock, so that's good! But I still maintain my point that's it's more bling than actual purpose.

 

all I know is that I had to resurface my passenger rear rotor a few times in the past and have not had to do so since I switched to drilled and slotted, because they allow for more coling.

drills and slots remove brake dust better.

Slots provide more airflow.

DS rotors give you better, more reliable, with more longevity, stopping power.

 

Actually slots and drilled holes do nothing for cooling. That's why your vents are there.
Did you even read my post entirely? Sorry, not trying to be an ass, but your statement sounds like the kind of thing I would read on an ebay seller page that sells DS rotors, lol.

How would it be more reliable if it cracks more easily?
How can it have more longevity?
How can it give you more stopping power?

Please back up your statements.

Here's a pic for you:

 

personal experience - warped my stock rotors twice in 60,000 miles. Had my D/S for 70,000 and no problems from them yet. Not sure if it's the better pads or rotors, or different driving habits. I'm satisfied with the stopping power I have, whether it's stock or better than stock - I don't know.


You do make valid points though, so I really appreciate you posting the information. I always wondered what "gases" people were talking about

 

No problem wink1.gif I like doing research (i do study in engineering after all!)

One thing you need to take into consideration:

Hyundai OEM rotors are shit.

I bought some UNP (i think?) plain rotors to replace them and they perform AWESOME compared to stock, and I've done all kinds of things with these. With PBR ceramic pads on them too.

It's just that the "Since I got DS rotors I haven't had problems" argument is used a lot. Not saying you guys are dumb or anything, but I'm trying to make you realize that if you got, say, some plain Brembo rotors, you would've had even more stopping power.

They look f***ing cool though, those DS rotors, lol, that's all they're good for IMO. With my BBK I might even go with that in order to have some bling since I have no more turbo and am just doing it as a "just cause i can'' thing. I just don't want to hear people saying they are more performant wink1.gif

 

1. Better quality materials = less cracking I'd expect cracking from e-bay materials.

2. longevity = works for longer. My stock rotors kept warping every 20,000 or so miles, my DS rotors have not yet after 30,000 miles

3. Drills and slots remove brake dust/irregularities in the pad. Drills and slots give that dust a place to go and keep the pad flatter. The slots divert it, but the drills kinda just take it up inside and fling it out later


And on gasses:

You breathe gas, aproximately 71% nitrogen, aproximately 21% oxygen and 8% other gasses. With little bits of brake dust on the surface, that's a larger area of the surface that cannot touch the rotor. If you remove that little bit of dust, you get more surface contact because the gas surrounding the little brake dust particles goes away.

 

Wow?

I will agree on the quality of materials like I said in a previous post. But that doesn't have anything to do with the rotors being DS.

As far as longevity goes, the fact that a stock rotor goes out after 20k miles means nothing compared to me stating a plain performance rotor would be better. You would have to test those as well in order to be able to use that as an argument.

Also, sorry, but whatever you are talking about air we breath getting under the pad, that's hilarious. I don't know how you came up with that.

 

^^ Yeah, I tried to read DTN's gas sentence three times but I still don't get it.

I think many people (me included) know this, but still get cross-drilled because they look nicer.

I read that in some racing applications they use cross-drilled rotors to save rotational weight, but they did mention that this was a tradeoff as the reduced mass/surface equals reduced cooling.

 

haha.gif


yea sometimes DTN goes off on these little rants, but seriously i'm going to agree that ever seince i put my D/S rotors on i've experienced better stoping perfomance. i think anyone who has them would tell you the same thing.

 

I agree with that optimo. DS might be better than stock. But plain performance (like a real brembo disc) is EVEN BETTER.

Catch my flow? smile.gif