Interesting article on upgrading brakes

[scubywrxr]

Its the last thing on a car modifiers list, yet its the first thing that should be upgraded(YES, the turbo and exhaust and chip comes later!) - Brakes on a car are overlooked until its too late to stop.

This is a test by C&D and is quite informative :
http://www.caranddriver.com/article.asp?section_id=4&article_id=2852&page_number=1

[SamuraiGti]

My brother changed his disc brakes, to a disc of AP racing and brake pads from ferodo racing. Didn't change the callipers.

Much Much better breaking now. I'll try to take a picture and then show here the discs, they look like an atom.

[zevolv]

My first car which I still have had the biggest brakes that would fit in the wheel which regretably was too small for the car so My dad bought a set of SVT 18" rims and we installed 15.3" 6 pistons in front and 4 piston rears from Brembo and now it feels like you could break your neck if you lay on the brakes all the way. The brakes on my EVO are perfect they are Brembos as well you gotta love Brembo. Hell 4 of our cars have them so they can't be all bad.

[veilsidebr]

pretty cool article..i agree with it, brakes must be upgrated first.

[graywolf624]

Cross drilled and slotted rotors.. yuk!

Always with the blingy bs.

I agree with upgrading the brakes first. But forget the cross drilled and slotted. At best they only hurt performance at worst they can get you killed.

[zevolv]

actually they help with braking under hard/hot conditions

[graywolf624]

"actually they help with braking under hard/hot conditions
"
<big clarkson pause>
wrong.

First slotted: the one which actually could be helpful. It was designed to get gasses away from the rotors. However most modern pads have grooves themselves that do this and thus don't have the trapped gas problem. They also output far less of this gas. In general it is agreed that the only possible benefit of these is that they deglaze your rotors, though at the cost of added friction/head disipation. In general in road racing some use them and some avoid(many say the glaze quickly fills the slots at which point they become useless.

Then drilled:
Designed originally for the same reason as above. When drilled without molding they decrease the structural integrity of the rotor. When molded (aka made with the holes)they still do but to a lesser extent.

Now for the physics.. The reason they dont help with heat.
The number one most important thing when braking is disipating heat from the pad to the rotor. metal conducts heat far faster then air. As such by decreasing the mass of the rotor you decrease its ability to disipate the heat away from the pad through the rotor. Thus the pads get hotter. Coupled with the structural rigidity problem Im sure you have a winner there.

For more brake knowledge read this thread. I'll also try to find you guys some articles.

http://www.altimas.net/forum/showthread.php?s=&threadid=32327&pagenumber=1


and another thread. Perhaps easier to read because the idiot vendor wasnt involved in this one.
http://corner-carvers.com/forums/showthread.php?s=&threadid=2002&perpage=40&pagenumber=1

So to recap: drilled equals bling.
slotted may have applications in rally racing and other high dirt/dust applications as well as possibly in deglazing (last part being a question of whether the benefits outstripe the costs. In general the answer is that the cost is greater then the benefit).

[coombsie66]

Then drilled:
Designed originally for the same reason as above. When drilled without molding they decrease the structural integrity of the rotor. When molded (aka made with the holes)they still do but to a lesser extent.



A single drilled perfectly circular hole in a plate, has a stress concentration factor of 3!! So wiv that many holes they do significantly weaken the discs.

I think that the holes do help cool the disc tho and prevent warping, they are after all adopted by BMW, Merc, Porsche, ferrari, etc etc! So they do have an application other than 'bling'
But i agree with you that in the after market replacements, if they are single piece discs, the holes will rarely do anything benificial!

[zevolv]

That's what I'm saying the Brembo's I have are the same ones used on alot of the factory cars. They are very good brakes.

[graywolf624]

"A single drilled perfectly circular hole in a plate, has a stress concentration factor of 3!! So wiv that many holes they do significantly weaken the discs.

I think that the holes do help cool the disc tho and prevent warping, they are after all adopted by BMW, Merc, Porsche, ferrari, etc etc! So they do have an application other than 'bling'
"

They don't help! sigh. Read Baers website sometime. They list it as the cosmetic fix it really is. Also read that thread for a analysis.

That they help cool the rotors is not important. Number 1 is the ability to take the heat away from the pad. They actually hinder this process. In fact. More stress is added to the rotors by drilling the holes. The cooler air around the holes makes a temperature difference that increases the stress.

Cross drilled are only for bling. They were designed to remove gases not help heat. They never help heat ever!!!! Read the threads. Both of them.

As for the manufactuers. First most of those designs have no similarities to the baers. 2 many of those rotors are ceramic and not steel. 3 Just because they do it does not mean they work.

Please read the threads before you comment. The people involved are experts and aren't trying to sell you something.

[graywolf624]

From the thread. Please read it.

You don't know the definition of "dissipate". You also don't understand the interaction between a rotor and the pads. Here is how it works. The friction between the pad and rotor is what causes you to stop. This friction converts your forward energy into heat (remember Einstein: Energy is neither created nor destroyed, it is converted). Now that heat is a bad thing. Yes it is bad for the rotors but it is a lot worse for the pads. A warped rotor will still stop the car - it will just feel like shit. Overheated pads however WILL NOT stop the car. It is here where the rotors secondary responsibility comes in. Its job now is to DISSIPATE the heat away from the pads and DISPERSE it through itself. Notice that DISSIPATE and DISPERSE are interchangeable? Once the heat is removed from the pad/surface area it is then removed. Notice where the removal falls on the list of duties? That's right - number 3. Here is the list again. Memorize it because I will be using it a lot in this post:

#1 Maintains a coefficient of friction with the pad to slow the forward inertia of the vehicle

#2 DISSIPATE the heat

#3 REMOVE the heat from the brake system

Let's look more in-depth at each step now shall we? No? Too bad assclown we are doing it anyway.

#1 Maintains a coefficient of friction with the pad to slow the forward inertia of the vehicle:
This one is pretty simple and self-explanatory. The rotor's surface is where the pads contact and generate friction to slow the vehicle down. Since it is this friction that causes the conversion of forward acceleration into deceleration (negative acceleration if you want) you ideally want as much as possible right? The more friction you have the better your stopping will be. This is reason #1 why BIGGER brakes are the best way to improve a vehicle's stopping ability. More surface area on the pad and the rotor = more friction = better stopping. Does that make sense Ace? Good. Let's move on.

#2 DISSIPATE The Heat:
Let's assume for a second that the vehicle in question is running with Hawk Blue pads on it. The brand doesn't really matter but that is what I am using as my example. They have an operating range of 400 degrees to 1100 degrees. Once they exceed that 1100 degree mark they fade from overheating. The pad material gets too soft to work effectively - glazing occurs. This means that a layer of crude glass forms on the surface of the pad. As we all know glass is very smooth and very hard. It doesn't have a very high coefficient of friction. This is bad - especially when I am coming down the back straight at VIR at 125MPH. Lucky for us the rotor has a job to do here as well. The rotor, by way of thermal tranfer DISSIPATES the heat throughout itself. This DISSIPATION lessens the amount of heat at the contact area because it is diluted throughout the whole rotor. The bigger the rotor the better here as well. The more metal it has the more metal the heat can be diluted into. Make sense? This isn't rocket science here d00d.

#3 REMOVE the heat from the brake system:
Now comes your favorite part of the process. This is what you thought DISSIPATION was. It is ok. I will allow you to be wrong. This is the step where the rotor takes the heat it DISSIPATED from the pads and gets rid of it for good. How does it do this? By radiating it to the surface - either the faces or inside the veins. It is here where cool air interacts with the hot metal to cool it off and remove the heat. Once again there is a reoccuring theme of "the bigger the better" here. The bigger the rotor, the more surface area it will have which means more contact with the cooling air surrounding it. Got it? Good.

Now let's look at why cross-drilling is a bad idea.

First - as we have already established, cross-drilling was never done to aid in cooling. Its purpose was to remove the worn away pad material so that the surfaces remained clean. As we all know this doesn't have much of a purpose nowadays.

Next - In terms of cooling: Yes - x-drilling does create more areas for air to go through but remember - this is step 3 on the list of tasks. Let's look at how this affects steps 1 and 2. The drilling of the rotor removes material from the unit. This removal means less surface area for generating surface friction as well as less material to accept the DISSIPATED heat that was generated by the friction. Now because of this I want to optimize step one and 2 since those are the immediate needs. If it takes longer for the rotor to get rid of the heat it is ok. You will have a straight at some point where you can rest the brakes and let your cooling ducts do their job. My PRIMARY concern is making sure that my car slows down at the end of the straight. This means that the rotor needs to have as much surface as possible to generate as much friction as possible and it needs to DISSIPATE the resulting heat AWAY from the pads as quick as possible so they continue to work. In both cases x-drilling does nothing to help the cause.

Now let's talk about strength - and how x-drilled rotors lack it. This one is simple. Explain again just how drilling away material/structure from a CAST product DOES NOT weaken it? Since you are obviously a man of great knowledge and experience surely you have seen what can happen to a x-drilled rotor on track right? Yes it can happen to a non-drilled rotor as well but the odds are in your favor when pimpin' bling-bling drilled y0! Since you are also an expert on thermodynamics why not explain to the group what happens to a cast iron molecule when it is overheated. I will give you a little hint - the covalence bonds weaken. These bonds are what hold the molecules together boys and girls. You do the math - it adds up to fractures.

So why don't race teams use them if they are so much better? Consistency? Hmmmm . . . no. I am gonna go with the real reason her chodeboy. It is because of several factors actually. They are as follows but in no particular order:

- Less usable surface area for generating friction
- Less material to DISSIPATE the heat away from the pads
- Less reliable and they are a safety risk because of fatigue and stress resulting from the reduced material

And what are the benefits? Removal of particulate matter and enhanced heat removal

Also please note that the air flow through the holes in a rotor are minimal due to the lack of air pressure differences.

[graywolf624]

More on the porsche reasoning for cross drilled.
"Discs are cross-drilled to enhance braking in the wet. The brakes respond faster because the water vapour pressure that builds up during braking can be released more easily."

You'll notice most porsche brakes dont survive track days and are huge in diameter(thus overcoming some of the negatives of xdrilled.)

[coombsie66]

quote from above:
"Now let's talk about strength - and how x-drilled rotors lack it. This one is simple. Explain again just how drilling away material/structure from a CAST product DOES NOT weaken it? Since you are obviously a man of great knowledge and experience surely you have seen what can happen to a x-drilled rotor on track right? Yes it can happen to a non-drilled rotor as well but the odds are in your favor when pimpin' bling-bling drilled y0! Since you are also an expert on thermodynamics why not explain to the group what happens to a cast iron molecule when it is overheated. I will give you a little hint - the covalence bonds weaken. These bonds are what hold the molecules together boys and girls. You do the math - it adds up to fractures. "

Ok he may b an 'expert' but he dont know bout materials!!!!! 1, no covalent bonds in iron!!!! It is a metalic structure, only a giant ionic lattice here mate!!! For this reason there is also, no 'iron molecule'!!
The reason the brakkes weaken upon overheating is due to the temperature to which the metal is heated to, and the speed with which it cools. As this affects the crystal micro-structure of the metal, and if the metal is not cooled in equilibrium then long colomnar grains in the direction of heat extraction are produced, these are not as strong as the other crystal structures that make up the metal (Body Centre Cubic, Face Center Cubic, Hexagonal Close Packed. etc)
I could go on 4 ages, but its rather boring if u dont follow it, i just wanted to show that this bloke, despite appearing to know lots, is correct in the effects, is not in theory.
I know he is not a member of this forum, and it isnt fair to pick holes when he cant defend himself here, but i just thought i'd point it out!! Plus he seems like he's rather up his own ass!!!!!!!!!
I shall read those other threads u linked to, and see if he's talking ny more shit!!!!!!
cheers

[graywolf624]

That is addressed by another member:

"1) The holes are cast in giving a dense boundary layer-type crystalline grain structure around the hole at the microscopic level as opposed to drilling which cuts holes in the existing grain pattern leaving open endgrains, etc, just begging for cracks.

2) The holes are only 1/2 the diameter of the holes in most drilled rotors. This reduces the stress concentration factor due to hole interaction which is a function (not linear) of hole diameters and the distance between them.

3) Since the holes are only 1/2 as big they remove only 1/4 as much surface area and mass from the rotor faces as a larger hole. This does a couple of things:

It increases effective pad area compared with larger holes. The larger the pad area the cooler they will run, all else being equal. If the same amount of heat is generated over a larger surface area it will result in a lower temperature for both surfaces.

It increases the mass the rotor has to absorb heat with. If the same amount of heat is put into a rotor with a larger mass, it will result in a lower temperature.

3) The holes are placed along the vanes, actually cutting into them giving the vane a "half moon" cut along its width. You can see that here:

This does a couple of things:

First, it greatly increases the surface area of the vanes which allows the entire rotors to run cooler which helps prevent cracks by itself.

Second, it effectively stops cracking on that side of the hole which makes it very difficult to get "hole to hole" cracks that go all the way through the face rotor (you'll get tiny surface "spider cracks" on any rotor, blank included if you look hard enough).

That's why Porsche rotors are the only "crossdrilled" rotors I would ever consider putting on my car.
"


I'm not a materials expert either, but I know they are right. Reading the entire thread gives the correct information. I chose this example (and his post) only because it stated the basic theory.

[graywolf624]

As for up his ass. Apparently you've never been to corner-carvers.com.

We find it disgusting that people would push this crap on the unsuspecting public without real info. Even more so that people blindly believe it. It is a place that you either bring the tech and physics to back yourself up.. or get banned.

Please note he is by no means the most expert of the group. He does have an impressive background as do most of our membership. This should also explain why I always jump on inaccuracies in threads.

[coombsie66]

^^ Nah ive never bin there, mite have a look!! Yeah that guy from movit appears to know a lot. Now i bet he did a mechanical engineering degree from a reputable uni! Cus no matter how much 'experience' you have it aint no replacement 4 the education in the 1st place.
It is reassuring to know that there is some warrented application of all this bollox that i spend hours learning 4 exams!!!!

[graywolf624]

haha.
Yeah john did a mechanical engineering degree somewhere. Almost all of the group are MEs. A few of them are engineers for racing teams or drivers.

If you wish to post you will need a sponsor. Even without posting it is a great place for disemination of knowledge.

[BACR]

thats a good review on brake upgrades, show u how important they are