Todd,

Can you approximate in a way that is meaningful the braking power for a few general brake modification options? (Specific to track events and R-compound tires)

For example, Using stock calipers and stock rotor size, what might a stock sized slotted rotor and really aggressive pads perform like compared with say a full on BBK?


I know fluid and SS lines help in other ways, so lets assume also that these components are installed too...if these matter.

 

Sure, I'll try.

First you must understand that there are four elements to brake torque; rotor OD, pad Cf, piston area and of course; pressure. Since you are only opting to change one of these (pads) the rest of the math stays the same.

Now go to my home page and open the TOOLS drop down. Select Brake Bias Calculator. We're less interested now in bias and more so in torque. Even using the default values you can see where a pad change from .40 to .50 will have a huge impact on rotor torque. But...the torque value is relative to the LEG value. Here's where the common "tires stop your car not brakes" comes into play.

Let's assume you put in 70lbs of LEG, that nets you X in torque. Now change the pad Cf to a higher number and bam; you have more torque. Great...so long as you are not locking the tire. Back the LEG down to get the same torque value and you'll see it takes less effort to achieve the same final number.

Now then put in 100lbs of LEG. (that's a lot of effort, trust me) and you are in a skid with the stock brakes and a .40 pad let's say. Change the pad to .50 again and the number is even higher. But, what LEG is required to reach the original skid? 100lbs = X tq with .40 or ?lbs = X tq with .50 pads?? The final limit it the tire. How you get there is what the changes offer you. Slots, holes, dimples or the like will not have any measureable effect that I can show. Clearly keeping the pad clean will help stabalize the pad Cf rather than building a boundary layer between the pad and rotor. So figure it's constant with or without if only changing pads. Reaction time also plays a roll. Stop hard...harder...harder...and you've used up time and space. Stop sooner by way of achieving max torque can speed up the time it takes to get to the full stop. Getting to the max of the tire sooner.

Beyond this there are many other issues about the BBK which make it generally superior. It's really less about distance and more about repeated stopping. Most stock part will continue to require more and more LEG for the same result as the pad heats up and the Cf drops. On a BBK the pads can heat up and stay there and often won't run nearly as hot given the efficiency of the package as a whole. Think of it as extended operating range, or insurance.

Lastly, open the Dynamic Dist Calc in another browser (or tab if run Firefox like you should!) and see what happens if you put the car into a .7g braking moment. Note the weight shift. This should be keeping pace with the proposed bias numbers to an extent. *note it does not currently account for prop valve issue.