So here I am browsing around while researching for a friend,(is doing a SR20 swap). And I stumble on this thread. I spend most of my time on corner-carvers.com and loved most of the replies to poor tech. Poor tech or poorly backed up tech deserves a good smack down. Assclowns abound with poor tech and it is good to see someone graciously show them the error of their ways. Humor is always a bouns. lookslikea240 was in over his head. but that's ok. however, lost-to-a-k-car, one point. first, you were dead on right up to your last post. you however, overstepped the discussion on brakes. I'll work it in your style:
2. "times line pressure"Bzzt. Sorry, Cooter. Tell him what he's won, Jim.Cooter's won an all-expense paid trip to Science Land, where he'll learn interesting facts, like- You can't measurably compress a liquid in an automotive hydraulic system!
Care to expound how this applies to the original statement? Noone said the fluid was compressed. So I fail to see what you are getting at and why it has anything to do with line pressure? I have always assumed in this discussion, that the hydraulic brake fluid is incompressible for all purposes and transmits all the applied force from the master cylinder to the brake pistons. Perhaps it is a semantics issue for you,(this is my chosen theme). I read line pressure to mean the pressure the fluid is exerting on the various surfaces it is in contact with.
- The pressure of the fluid in the system is irrelevant to the force applied to or extracted from either end of the system!
Ok then, I'm game - what is? Am I to assume that the piston will move of its own free will? Perhaps it is some of that magic you refered to earlier. Some force must move that piston and then allow it to exert force on the brake pad. Pressure is a measure of force. Or more specifically, force applied to an area. So if I put a force on one end of a hydraulic line, and nothing can move on the other end of this line,(and for this discussion, we will assume the line does not expand). Then that force applied at one end will be distributed evenly through the fluid and the fluid will extert pressure equally throughout the line. Now lets stick a movable piston on the other end. As we apply pressure on the brake pedal, increasing the pressure in the system,(line pressure), the resultant force,(the pressure distributed over an area) on the piston will cause it to move. But since we are dealing with an incompressible fluid, if we didn't continue to move the brake pedal, the piston would stop immediately. However, we move the brake pedal, which moves the fluid which moves the piston until it hits something causing it to stop. Now as we continue to increase the pressure on the brake pedal, that pressure is transmitted to the surface of the piston. If something is in the way, like say a pad and a rotor, that pressure will be transmitted into a force on the rotor. So by my take, our force on the pedal, which increased the "line pressure" is now translated into a resultant "push" on the rotor, or a force on the rotor. So break it down for me. How is the pressure in the system NOT transmitting the force we are putting on the brake pedal to a resultant proportional force on the pad? Again, a pressure is a force over an area. So we take a pressure and apply it to an area,(the piston), we now have a resultant force. Again, if you are just playing symantics to screw with lookslikea240, so be it. However, the result is misleading for the rest reading this thread.
- You don't multiply the area of the piston face by anything when calculating the force in a hydraulic system!
Ok, then what are you refering to? You DO multiply the pressure in the "system" i.e. the lines, by the surface area it acts upon,(in this case the brake caliper pistons), to calculate the force exerted on the back of the brake pads. Again, you may be playing a symantic game. But bottom line, the pressure in the system times the area it acts upon gives you the force it exerts on the surface in question. In this case, the line pressure times the piston area,(all the pistons area), equals the force applied to the back of the brake pad, and in turn to the surface of the rotor,(with another area to deal with). Now we didn't even get into rotor diameter having a greater leverage, etc.. But that was not really part of the discussion. But it was discussed earlier:Exar-Kun said...larger diamter rotors major benifit is from the increased surface area and therefore cooling/heat absorbing ability of the rotor
Correct. They will cool more efficiently, which will reduce fade. This is the benefit of larger brakes, not faster stopping.
If your brakes aren't fading, the upgrade won't do anything for you. Sopdadope's friend Dave autocrosses, so he probably already understands this and has the upgrade for the right reasons. You left out one very important issue. First, the major benefit of a bigger brake upgrade depends on the stock system. Some systems have way too little mass in the rotor and heat soak the rotor quickly. Others are just undersized and cannot exert much work on the tire to slow it down at high speeds. Sometimes a bigger brake upgrade is a larger diameter rotor with a stock caliper. So then the question is will a larger diameter rotor perform better assuming the same overall mass? (yes, unlikely, but just assume for my theoretical example) Absolutely. It is levereage. But let me clarify. Your last statement that if they aren't fading the upgrade won't do anything for you is only partially correct. With a larger diameter rotor you can effect more leverage on the rotor,(and hence the tire). This is most obvious at higher speeds where the rotaional speed,(dealing with high levels of inertia now) of the tire is high and very few stock systems can lock up any tires,(talking 100+ mph). At that point, the larger diameter the rotor, the more leverage the caliper,(pads), have on the rotor and the more work they can accomplish. This will obviously pump much more heat into the system for a give max performance stop. But I am assuming the rotor can handle it for my example. You always maintained that if it can lock up the tires, bigger brakes won't make a bit of difference. And I agree 100% since you were refering to below 60-70 mph. However, on the track, mass of the rotor is most certainly an issue, but the leverage the brakes calipers,(really the pads), can apply to the rotor directly affects how well it can stop. And Nils, one comment: Prove it to me..... a buddy of mine used AP brakes first with regular plain rotors for a 20 minute session, we then changed to slotted rotors, went out again for 20 minutes and when we put the heat gun to it it showed lower temps. That is real life track proven stuff, I dont know what you got..... First, you are missing some information to give out that kinda data. First, was the first rotor used or brand new for the 20 min session as the second slotted rotor was? Were they manafactured by the same company, i.e. brembo vs someone else? And what type of heat gun did you use? Did they follow the exact same procedure for each measurement? Was their a cool down lap or was this pulled in right after a hot lap and close to another braking zone? Did they brake easy or hard coming into the pits? Not trying to berate you, but all those have a rather significant impact on the readings and you didn't offer any of that info for us. Did you realize that a surface pyrometer gives much more accurate temperature readings than a infared pyrometer,(i.e. a gun)? This becomes and issue when you are reading temps from something that is really shinny, such as your brake rotors.... That is why I ask. Not saying you didn't see the data you said, but rather it may be inaccurate because of the measuring method/equipment. Take a look at all the serious high level road racers,(IMSA, F1, Touring car). You will not find any slotted or crossdrilled rotors. They all go with solid. All the slotted rotors do,(besides give a place for a crack to start), is accelerate your pad wear. Yes, there is some effect to "cleaning" the pads. That is precisely what accelerates the wear. However, it is possible that with the setup you had, the pads were beginning to glaze over,(on the regular rotor), and became less effective, causing the driver to need to apply more force to the system to effect the similar braking,(was likely reduced effectiveness, causing increased braking distances, and more heat being pumped into the system). With the slotted rotors, the glazing issue is really not there, so it may have corrected a weakness in your braking system,(I assume you are refering to another heavy supra...
). And this comment:A slotted rotor will do it even quicker beacuse it channels cool air more effeciently over the rotorThat is just patently false. Can you describe the airflow over the surface of the rotor? Can you say turbulent flow? The slots, as discussed above, only serve to wipe a little more material from the pad each pass. It may correct a deficiency in the system which is causing the pads to glaze. Any inperceptible increase in cooling,(unlikely at best) is more than offset by the decrease in mass from the removed material. In either case,(cooling or removed mass), the effect is so small, you won't even notice it. Again, I refer to my above comments about the possible reasons why your readings were lower. -Bobthis ought to be fun
It was the first time I had ever seen a XJ220, and to see it on the track was great. I am always happy when I see people with great cars take them out on the track. I love it when I see the exotics out on the track. The Ferrari's,(there was a 360 challenge car there this weekend), the Speed GT Porseche Cup cars were there,(3-4). There was a full blown GT-1 tube frame C5 corvette there to name a few. And to think, this was just a NASA event with a HPDE thrown in.-Bob<edit>added what value there is in computing system pressure,</edit>
