Cross Drilled VS Slotted Rotors

[Ragnarok043]

well drums are more prone to locking than disc. drums are also not only heavier but adds more to the rotational mass of the rear wheel than disc.

[Targa250R]

Originally Posted by shaolin_style

I have a question. On my EG I'm still rocking Drums in the rear. How much performance would I actually gain switching to discs in the rear when about 75% of your braking is done at the front??

None. There is no difference in braking whatsoever by swapping drums to discs in the rear of a Civic - and testing has backed this up. The main benefits of discs are better heat dissipation, better friction compound selection, and ease of maintenance. Many also prefer them for appearance purposes.

I mean for Auto-x. I think for street use its not worth it to upgrade to rear discs.

Street driving actually requires more brake heat capacity than regional Solo autocrossing does. If you don't think it is worth it for the street, then it isn't worth it for autocrossing either.

Autocrossing has completely different brake requirements vs. track days. For autocross, the weight benefit of smaller brakes is typically more important, whereas for track days, the heat capacity offered by more massive brakes is typically more important.

Originally Posted by Ragnarok043

well drums are more prone to locking than disc.

Um, no. That's way too general of a statement to be accurate. I know the point you're getting at, but you've misunderstood it. This is not true.

drums are also not only heavier but adds more to the rotational mass of the rear wheel than disc.

No, you're wrong. The ubiquitous 4x100mm 9.5" solid rear disc setup with 7CLP13S calipers weighs at least 7lbs more per side than standard Civic drums do. Thats a gain of 14+lbs of unsprung mass.

[mike_sho]

Originally Posted by Targa250R

None. There is no difference in braking whatsoever by swapping drums to discs in the rear of a Civic - and testing has backed this up. The main benefits of discs are better heat dissipation, better friction compound selection, and ease of maintenance. Many also prefer them for appearance purposes.


Street driving actually requires more brake heat capacity than regional Solo autocrossing does. If you don't think it is worth it for the street, then it isn't worth it for autocrossing either.

Autocrossing has completely different brake requirements vs. track days. For autocross, the weight benefit of smaller brakes is typically more important, whereas for track days, the heat capacity offered by more massive brakes is typically more important.


Um, no. That's way too general of a statement to be accurate. I know the point you're getting at, but you've misunderstood it. This is not true.


No, you're wrong. The ubiquitous 4x100mm 9.5" solid rear disc setup with 7CLP13S calipers weighs at least 7lbs more per side than standard Civic drums do. Thats a gain of 14+lbs of unsprung mass.

Street driving does not require more heat capacity. It requires more initial bite for safety. Highway or high-speed driving does though, perhaps thats what you meant. Otherwise auto-cross requires more , but it also depends on the course. Some courses you can get away with very little braking , others theres a lot of it. So thats hard to say either way.

Drums , seem to be a bulkier system. Therefore a weight gain or loss isnt exactly straight cut one to the next , a more compact system (brake rotor and caliper) can perform the same given its smaller. But at that weight difference its hard to say at that point. Most likely your right , but just wanted to note that when it comes to unsprung weight it all depends on where the weight is at. Like they say , spin in a circle with your arms out , now pull your arms in. Same weight , much easier to spin with the arms in.

Another side thought though is rear brakes really do nothing for power , if a rotor system can brake more effectively it would be nothing but a weight gain. The other non-benefit to the rear would be the unspung weight on the actual suspension. Which 14lbs is quite a bit , but its nothing to write home about , the performance difference is negligable either way , but in theory it is something. Is it enough to show up in a 1/4 mile , perhaps. How much , who knows.

[Targa250R]

Originally Posted by mike_sho

Street driving does not require more heat capacity. It requires more initial bite for safety. Highway or high-speed driving does though, perhaps thats what you meant.

Street driving includes highway and some high speed use. For some, it also includes long descents with extensive brake use, for which most people don't practice a proper braking technique and thus create a lot of heat.

Otherwise auto-cross requires more , but it also depends on the course. Some courses you can get away with very little braking , others theres a lot of it. So thats hard to say either way.

It is course dependent, however in general you don't need a lot of heatsink capacity at all for autocrossing - however you do need a friction material with a broad operating temperature range and stable bite curve, good modulation characteristics, and a high enough friction coefficient to lock the tires that you're using. The stock brakes with an upgraded friction compound are almost always plenty for most cars.

Most national-level autocross cars are not using massive brakes. A purpose-built autocross car will almost always have the smallest brakes allowed by rules to save weight. As an example, the highest-finishing Honda in Street Modified for several years running - owned and driven by Chris Travis - has been an EH3 Civic hatchback with stock 9.5" vented front rotors and the small unmarked Civic calipers, coupled with rear drums from a non-Si/non-ABS model. Travis actually had been using 5-lug ITR brakes (11.1" vented front rotors with 17CL15VN calipers and 10.2" solid rear rotors with 9CLP14S calipers) previously, but converted back to the smaller 4-lug brakes for a significant weight reduction.

As I've explained before, you can't approach autocross with the same mentality that you would drag racing, street driving, or track days, because there are fundamental differences in the way the cars are used, in what is necessary for the car to do what you need it to do, and for competition applications, in what is beneficial to reducing times.

[shaolin_style]

Thanks alot for all the info guys. Looks like I could put 3-400 bucks to much better use than getting rear discs

[mike_sho]

Originally Posted by shaolin_style

Thanks alot for all the info guys. Looks like I could put 3-400 bucks to much better use than getting rear discs

Goto a junk yard and yank em yourself , im sure you could get away with a nice deal if you can find them. But yeah if money is scarce and your not pushing the car hard with power , brakes arent really needed.

I normally monitor the brake system as is , put it through some tests and if it does provide a safe basis for my aggressive driving then perhaps. But otherwise street setups should provide ample for most. If anything some nice pads are a good start.

[shaolin_style]

I finally build a decent motor (211 whp) but my car is stopping fine with just the fronts upgraded. The car is COMPLETELY gutted spare the dashboard so its lightened up alot which helps stopping too. I think I'm gonna try and find some sway bars to finally finish off the suspension. Any tips on sways or should I start a thread?

[pwrusr]

Blank rotors will almost always be stronger then drilled or slotted rotors. They (blanks) have more surface area for the pads to actually grab. drilled rotors in any form are just not worth it IMHO. I don't care how they are made. They tend to crack much eaiser then any of the others listed here.

In etheir case with etheir type of rotor you can't turn them at a brake shop to get the rotors surface clean and fresh again. Also NEVER EVER use slotted or drilled rotors on the rear disks. That's just not safe at all. Because the rear rotors on most hondas are solid and unvented. when a crack forms it goes stright through from one side to the other.

[pwrusr]

I was going to have this all in one post but it was a little too long to have in one post. so here's the continueation of the above post

I found a fantastic brake infomation post in another forum that really drives home the point I'm trying to get at:

First, lets get some physics. Tell me how a heatsink with less mass will cool better? You do realize that a brake rotor acts as a large heatsink to transfer heat from the brake pads to the rotor. The heat generated from pads has to go somewhere and so it transfers to the rotor and caliper.

Porsche claims: "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."

They have said nothing about enhancing normal braking circumstances and the larger diameter rotors probably make up for the lack of material present in a smaller cross drilled rotor.

From Wilwood's website:
QUOTE

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.



As for the porsche rotors, a few notes from a forum I frequent:
QUOTE

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.

BTW, many of the above features are not present in older Porsche brakes. The above is for "Big Reds" and newer.



This is quite different from the standard drilled rotors you get from brembo/kvr/powerslot/"insert random ricer parts brand name here" brake rotors.

Further proof of the uselessness of cross drilled rotors are found here:

http://www.teamscr.com/rotors.htm


Then from Grassroots Motorsports:
QUOTE
"Crossdrilling your rotors might look neat, but what is it really doing for you? Well, unless your car is using brake pads from the '40s and 50s, not a whole lot. Rotors were first drilled because early brake pad materials gave off gasses when heated to racing temperatures, a process known as "gassing out." ...It was an effective solution, but today's friction materials do not exhibit the some gassing out phenomenon as the early pads. Contrary to popular belief, they don't lower temperatures. (In fact, by removing weight from the rotor, they can actually cause temperatures to increase a little.) These holes create stress risers that allow the rotor to crack sooner, and make a mess of brake pads--sort of like a cheese grater rubbing against them at every stop. Want more evidence? Look at NASCAR or F1. You would think that if drilling holes in the rotor was the hot ticket, these teams would be doing it...Slotting rotors, on the other hand, might be a consideration if your sanctioning body allows for it. Cutting thin slots across the face of the rotor can actually help to clean the face of the brake pads over time, helping to reduce the glazing often found during high-speed use which can lower the coefficient of friction. While there may still be a small concern over creating stress risers in the face of the rotor, if the slots are shallow and cut properly, the trade-off appears to be worth the risk. (Have you looked at a NASCAR rotor lately?)




And then, let's check out what was said on the aforementioned Altima thread [[[ Long thread at altimas.net that was deleted by that server. it is hosted here ]]]:

QUOTE
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. I gotta tell ya - it is a tough choice but I think I am going to stick with the safe, reliable, effective-for-my-stopping needs solution Tex.

[westcoast268]

Has anyone heard of a company in california called rotorworks? if so can anyone tell me if they sell good drilled and slotted rotors