There is a thread that leads into braking theory that most of you should probally read. It covers topics such as Why crossdrilled rotors are stupid. Heres a link http://corner-carvers.com/altimathread.php.html Its a long thread, feel free to discuss More links less forums http://www.teamscr.com/grmbrakes.htm http://www.teamscr.com/rotors.htm http://www.stoptech.com/tech_info/tech_white_papers.shtml http://www.howstuffworks.com/tire.htm http://www.howstuffworks.com/fpte.htm
If you ever do Scotts Driving School he goes over this. This guy is missing a key factor though in Brake Theory and Maybe SS will chime in, but if I remember correctly, Scott explained to us thaty with Crossdrilled Rotors, it is normal for gas bubbles to form in the holes which make it harder for the pads to make contact with the rotors which can cause bad brake fade. With the Slotted rotors, the slots are designed to push those pockets of gas out and away from the rotor and allow good contact with the pads for excellent stopping power.
I am going to have to respectfully disagree, and go with a brake expert on this one. Hold for qoute.. IN 5 4 3 2 1 Crossdrilling Crossdrilling your rotors might look neat, but what is it really doing for you? Well, unless your car is using brake pads from the 40’s and 50’s, 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’. These gasses then formed a thin layer between the brake pad face and the rotor, acting as a lubricant and effectively lowering the coefficient of friction. The holes were implemented to give the gasses ‘somewhere to go’. It was an effective solution, but today’s friction materials do not exhibit the same gassing out phenomenon as the early pads. For this reason, the holes have carried over more as a design feature than a performance feature. Contrary to popular belief they don’t lower temperatures (in fact, by removing weight from the rotor, the temperatures can actually increase a little), they create stress risers allowing 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.) The one glaring exception here is in the rare situation where the rotors are so oversized (look at any performance motorcycle or lighter formula car) that the rotors are drilled like Swiss cheese. While the issues of stress risers and brake pad wear are still present, drilling is used to reduce the mass of the parts in spite of these concerns. Remember – nothing comes for free. If these teams switched to non-drilled rotors, they would see lower operating temperatures and longer brake pad life – at the expense of higher weight. It’s all about trade-offs. Slotting 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?)
i haven't read those articles yet, but if there are no "gases" (at least enough to warrant slotting), then where does the "brake fade" on modern brake configurations come from? nothing becomes vaporized on modern pads?
Modern brake fade comes from excess heat in the brake system I think. I.E. Rotor being to small, or to thin, not enough mass The slotting cleans a small amount of material off the pad each time it passes, so that they dont glaze over.
very interesting, i have often wondered how much the life of a brake pad reduces, when using drilled or slotted rotors. as well as the less mass heating up quicker.
man there are some ignorant people on there. One of them quoted Einstein's Mass-Energy relationship, when he was trying to explain Newton's 1st law of thermodynamics and the law of conservation of energy, which leads me to believe that none of them in fact know what the hell they are talking about. And then saying "i know because i am an expert in the kinetic energy/thermodynamics area" haha
Yeah the thread get pretty deep(in poop), but the tech articles I posted up are pretty good, especially some of the stop tech stuff, you GA Tech boys should like that one.
So why does Porsche still use massive cross drilled rotors? Seems like the Porsche engineers would stay away from a product on their vehicles that only adds "bling"... Clarification...this is an actual question, not a statement.... Another link I found trying to answer my own question: It doesn;t answer it, but seems like more good info: Baer
You say porsche engineers would stay away from it because it only adds bling, I say they put them there just for bling. Thats what 95% of the exotic car market wants bling.
got to agree with that. Its sad that most people that have them, use them as a status symbol. so, every little thing that says "Look at Me" will be on there, functional or not. I'm not saying that Porche doesn't have some awesome engineering, but come on some of the stuff is overkill.
that said, it's also good to remember that they wouldn't want to add things that would hurt performance, they do afterall still have to maintain the integrity that originally made them a status symbol of performance. and they are... german.
=minimal, form following function, and yes anal as hell engineering. i've worked with german designers before. they're SCARY good.
Modern brake fade is caused not by the pads, but by your fluid. As your brakes get hot, the brake fluid inside your calipers starts to boil & turns into vapor. It's still in the brake caliper (it's not leaking out, usually...), but now rather than trying to compress a fluid, you're compressing a fluid/gas mix. This is why the pedal starts to feel spongey or soft when you start to experience brake fade. Rather than all the compresive force acting on your brake pads, now some/most/all of it is being used to compress the vapor, which is much easier to compress. If you're really curious about this, next time you go to buy brake fluid, check the back of the bottle for the boiling point. The higher the boiling point, the more resistant it will be to brake fade. Good manufacturers will actually list both dry & wet boiling points, as brake fluids like to absorb moisture out of the air, and over time this reduces the boiling point. So 'dry' refers to new brake fluid, and 'wet' refers to old brake fluid that has been in your system for a while. You'll note that the wet boiling point is usually 100 degrees or more below the dry one. This is why it's a good idea to change your fluid before a major track day. -Laters! -Chris!
Just to chime in with my 2 cents on the matter. I would like to briefly discuss brake fade, and help bring a little bit more clarity to the thread. There are in fact 3 types of brake fade. Pad Fade, as stated, this is when the pad is literally too hot to cause any form of abrasive friction to the rotor, or vapor is between your rotor and your pad. NEW PADS CAN STILL DO THIS. Im not quite sure where that was read that new technology does not cause that but that is incorrect. New pads can still suffer from vapor lock under extreme temperatures. Pad lock? This is when you're giving the pedal 150ibs of pressure, its still firm, but you're not stopping. There's no contact between pad and rotor because of the vapor present between them. Fluid Fade, this is when you boil the fluid. This boiling creates vapor, commonly referred to as "air", and creates the spongy pedal feel that everyone knows and loves. Brain Fade, more common than people would like to believe. This occurs when you begin to miss your own apexs, turn in points and braking markers. This is your basic fatigue and rarely receives enough credit. This can easily be as much of a problem as the other two above. I do believe that a Novice driver will suffer from Pad and Brain before Fluid, however, the stock fluid is not that difficult to boil if you're demanding enough on it. I would recommend to anyone interested in AutoX or Tracking that they invest in Fluid (ATE, Motul, AP Racing), Pads (Carbotech, Hawk) and SS Lines (Goodridge, StopTech, etc). One more thing. Its difficult to discuss all of this without paying attention to your tires. If they're greasy, no matter of braking will improve your stopping power. You may as well run a cool down lap and pit in to let the tires cool off. Outgassing is not very common on street cars, and so this is why we couldnt figure out why Porsche, Corvette, etc still cross-drilled rotors. Granted, its apparent that these companies do so on their street vehicles to give them that racy look that the car represents. In retrospect, it is also a matter of safety. Cross-drilled rotors can provide a safety and performance advantage in wet weather. Most people’s brakes won’t work right after they drive through a puddle because water gets between the brake pads and the rotors. The holes in cross-drilled rotors actually give that water someplace to go, so the brakes will work right after you splash through a serious puddle.
Ah, I keep reading more and more in that thread that I disagree with. This is not my understanding at all. Heat dissapation IMO was a bonus to the original intent of Racing Teams drilling their rotors. In the old days, particularly on race cars, when the brakes would get hot they would boil off a material in the brake pads (outgassing). This gas would get trapped between the brake rotor and the pad, which would prevent braking. To release the gas, people began drilling holes in the brake rotor. Slotting the rotor is a newer technique that produces less stress on the metal, and therefore provides increased rotor longevity. This has nearly the same effect of gas removal as cross drilling.
The problem with this statement is that, the pad gets too hot because the rotor can not absorb any more heat, so really it isnt pad fade. A larger rotor with more surface area and or greater mass would dissiapate (sp) more heat.
Alright, I will agree there. I mispoke. There is a point where you have 0 adhesive and 0 abrasive friction. As well as there is a point where you can experience vapor between pad and rotor. Yes, I agree with you 100% on rotor size. A larger rotor not only allows more braking control due to its larger surfrace area it will certainly take longer to heat up to a point of absolute failure.
I had this hunch that Porsche Racing probly dosent use crossdrilled rotors... did some research and it turns out that..... Porsche Racing does not use crossdrilled OR slotted rotors... they use internally vented rotors... thus, supprtoing the fact that Porsche uses the crossdrilled rotors on street applications for the purpuse of proper function in less than ideal road conditions, i.e rain..... i couldnt find a good downloadable picture of internally vented rotors.. but if you go to http://www.porsche.com/all/motorsport/rsspyder/pcna.asp and click start.... technology... and suspension.... it will show you a great picture.... most of Porsche Racings cars have used this type of rotor i.e all the 911 gt3's they race in le mans and porsche cup
right, but still we're talking about street applications, not F1, so slotted rotors would allow the gas that will inevitably build up on (what 330mm for our cars?) the track to go somewhere. IMHO, you can call me stupid all day long, but i'm ultimately putting slotted rotors on my fronts when i get to the point that would warrant it. fade of any kind as most who just took scott's class will tell you, is very disconcerting, because when it happens, you're already too "hot" for that turn. then it's salad tossin' time lol.
:rofl: whoopsy But yes, ultimately, I will seek slotting my rotors, or more than likely purchasing slotted rotors when these are dead. Yes, I had a lot of fun with a spongy pedal going into the Carosel at 105mph.
My point wasnt to say that Le mans, F1 do everything right..... it wsa to say that Porsche and other street car engineers(i.e. those who work on the viper and vette) have a reason for putting crossdrilled rotors on the car... they function in all weather, you have to remember these dealers/designers do not intend for you to push the limits of there car(race) on the street(therfore not expecting you to push their brake systems to the max on the street either) another thing to consider is that, after talking to the Porsche service guy this morning.... Porsche Racing does not use slotted or crossdrilled rotors because like nascar and F1 and indy and all the major race leauges you can imagine... the car is completly stripped and rebuilt.... the brake system only has to work once then it is rebuilt to be like brand new EDIT: after reading this i desided that i sounds like i am trying to say slotted and crossdrilled are bad and that is NOT the case.... i pretty much agree with Alex .... rotor mass is going to be the main factor how hot your pads get and will the more massive you rotor helo you stop faster( pad are also very significant here).... Crossdrilling, while this will greatly help in poor driving conditions it raises the chance of craking a rotor( which we all know stinks) and reduses mass which can potententially equal higer temps... If you are a person who isnot going to track your car or eveng go on mountain runs the cross drilling should be a safe way to add some bling to your car while also adding the ability to stop with wet or slick rotors/pads Slotting, Its a trade off... this like discussed before is going to give you a midddle ground... it will not reduce the mass of the rotor by much so operating temps will not potentially change, and it still gives debris( i.e. water, gas, dirt,)somwhere to go when the pads are forced together, also slotting does not lead to craked rotor near as often as crossdrilling. Those who push their car moderatly and go to a few track days each year...(most of us on this site) i think should consider slotted rotor... they are not as bling as crossdrilled but are going to give us reliability under the conditions we throw at them.
Man, this is a damn good forum!!. There is so much to learn about these eccentric vehicles we call subies...LOL... Mark...aka...The Silver Bullet....
I just ordered slotted rotors but they are OE wrx size so obviously not going to see a response like on an STI but should be better than stock...can't wait to test them out!! I'm with Mark, very informational post here!!
Scott, I am glad that you got your rotors, man....I tried to send the pics via your e-mail @ Yahoo. The e-mail came back. PM me your e-mail address when you have time. Mark
Scott, definately seek upgraded brake pads and upgraded fluid (higher boiling point) to ultimately utilize your new rotors.
Well, it looks like Alex was paying attention in class Modern pads CERTAINLY still out-gas when you over-temp them. The holes do give that gas somewhere to go. It's not a great fix, and it's not even something I would suggest any of you pursue, but it does help if/when you over-temp the pads. Something to note about lightening the rotors - they also cool faster. The more mass you have, the more temp you can absorb, but also the more mass you need to cool. For the VAST majority of Subaru drivers *ALL* you need, even on a road-course is upgraded pads and fluid. Let's say stock pads have a good coefficient of friction from -100 degrees to 600 degrees. Then they start to over-temp, the CF goes away, and eventually they out-gas. Better pads have good CF from 0 degrees to 800, race pads are more like 200 (so they need some heat) to 1400+. So with race pads you can "GLOW" the rotors and still have brakes. I'll post some more in a bit. Gotta tune SS
We are going to have to disagree here, when you drill the rotors you are treating the symptoms and not the problem. The problem is that the pads are over temp. If the rotors were larger or the pads were better then you wouldnt have that problem. They may cool faster but they cant absorb as much heat. To have the perfect brake setup you would need a diffrent one for each family.
ABSOLUTELY!!! I agree fully. You are treating the symptom, not the problem. That's what I was trying to say, but you are correct. The "right" pads don't over-temp and out-gas. All I was trying to say was that if you do run into that situation, THEN the holes help, not that it is an acceptable solution. The braking system needs to be right. If you had plenty of ducting, on the right tracks you could have nice light rotors that would cool between braking zones. SS
I did not bring up lightweight setups (which I've done substantial research on) because I did not feel it was necessary to the discussion Glad this thread is still chuggin along though
Good then we are in agreement. By the way, I picked up some axle seals from you guys the other day and there was a Black forester with black steelies on it, looked like it was lowered, might have had a front mount. That was a cool looking ride. I dont know if they are a member on here but that thing was sweet looking
I read about how much more front-biased the WRX is in various forums, and I do notice a 'front weight dive' under hard braking that I dont as easily in other cars. if you lowered your ride height, would that increase the potential stopping power of the rear brakes?
Lowering If you lower the car more in the front or the rear you are going to change the weight bias some what, however I would think that the same amount of weight still transfers to the front under braking so I would think that the Brake Bias would still be similar. I dont have any hard facts about this so please dont hold this as absolute truth. Ill do a little digging to night to see what I can find.
lemme know... i kept reading about how doing an H6 rear brake conversion is a good idea for a wrx, but after reading all these guides, i wondered if just lines, fluid, and lowering ride height would be more effective & less complicated for a one time investment.
I'm entirely way too tired from last night to really think about this, but what you said makes sense. If you lower the car, you are changing your cg, however, this shouldnt necessarily affect the weight transfer should it? All other variables remain equal.
meaning the weight is not going OVER the front suspension as much as it is just going forward on a more level plane. like, the taller, or higher over the suspension the car is, the more the whole weight of the car lifts completely from the rear like a see saw
The thing is I'm not sure of is the weight transfer, if you lower the car does it really effect the weight transfer or does it change the dynamics of the weight transfer. For example does it delay the transfer of weight from the back to the front under braking or is it not simply the lowering of the car but is it a function of the rebound settings of the shocks. More rebound damping in the rear shocks might delay the transfer of weight to the front. Oh the dynamics of the racecar. Matt
^^^ Of course I have an "opinion," well not really an opinion The *ONLY* ways to reduce actual weight-transfer is to: 1) Lower CG 2) widen the track Imagine that each axle is a triangle, with wheels as the lower two corners, and the cg as the top point. Lateral load "works" on the CG. That's where the load is "pushing." If the CG is higher, it's "tipping" it harder, more transfer onto the outer wheels. The wider the track, the further the "edge," the less weight that is moved from one to the other. Stiffening the suspension reduces ROLL, but *NOT* actual weight transfer. This is the hard concept to get, and actually not as important as it sounds. With the same CG height, and same wheel track, the same lateral load (acting on the CG) with the same track width still equals the same load transfered from the inner wheel to the outer wheel. The reason it's "not that important"* is that the alignment of the tire is a good bit more important than how much weight you're taking off the inner tire. That's the "main" advantage of stiffening; it keeps that outer tire flatter on the ground. * the reason for all the stars and quotes is that once you do have the outer tire flat on the ground, the weight transfer is important, so lowering again becomes helpful. The reason you shouldn't over-lower the cars is the camber curve, but that's a topic for another post. SS
Thanks for chiming in scott, that makes perfect sense. Also, we should get a post going on the camber curve, or at least an addition to my alignment thread.
Thanks Scott, that was an excellent description. I couldnt figure out how to word it so that everyone would understand it. Matt
Here's a quick thing about not lowering too much. I meant to take a pic of a car that was WAY too low, that also had hit the curb HARD, but anyway, here's the thing about lowering too far: The lower control arms (LCA) go from the chassis to the bottom of the wheel hub. The top of the wheel hub is fixed to the strut. Imagine that your left fore-arm is the driver's front wheel hub. Hold your left arm vertically in front of you. Put your right fist on your left elbow. Your right fore-arm is the LCA. If your right elbow is higher than you right fist (stock height where the chassis is higher than the wheel) you can see that as the wheel (your left arm) rises (suspension compression by body roll) you fist, and therefore the bottom of the wheel hub swings outward. With the bottom of the wheel moving out, you are gaining negative camber. This is good, more grip with more load, good thing. If you lower the car, raising the wheels into the chassis, it's like raising your left forearm until your fist is higher than your elbow. You can see that as you compress the suspension now, your fist, therefore the bottom of the LCA swings IN toward the chassis. So you are now losing negative camber with load. This is not a good thing. This is less grip with more load. Hope this helps, SS