KH Discs vs 73+ Discs
Why are you determined to pick a fight?
I don't claim to be a brake guru, I leave that to those who truly are. I just have some experience in the field of designing them.
I'm not trying to pick a fight. You were the one that said you designed brakes. You're pushing your opinion on people that are actually trying to decide what brakes to use, to the extent that you told another member that he didn't make the best brake choice. Yet, you have provided no evidence to back this up. In post #5 you says "Rotor diameter and total caliper piston area are everything in brake torque." In post #72 you say "Smaller piston area means nothing by itself, adjust the mechanical leverage ratio and/or the m/c bore size to achieve the pedal feel desired. "
All I'm trying to do is make this clear for folks that are trying to pick a set of brakes.
If you want to nit-pick, I struggle to understand why both sides of a fixed caliper's piston area aren't included in that calculation - they both are working to stop the vehicle, hopefully. You only count one side of a sliding caliper because it only has one side. So for parity's sake, why not double the slider's piston area? The backside of the slider piston bore is effectively the opposing piston. I don't have trouble with the formula, I don't know the history of how it came to be and that's what I struggle with. I didn't derive it.
This is simple, it's Newton's 3rd law. The single piston slider exerts just as much force on the backside of the rotor as the front. The formula doubles the area of the pad to reflect this for simplicity, because it's the same force as on the other side. The formula does take into account both sides, as long as you publish the formula properly, which you didn't. You left out multiplying the friction coefficient by 2. From Stoptech...
Tw= Ps x AP x µ x 2 x Re
Tw= Brake torque at the wheel
Ps = Pressure of system; AP = Total Area of pistons in one half of caliper (one side of opposed type or active (piston) side of sliding or floater type);
µ = Friction Coefficient; x 2, since there are two sides of the rotor that the pads are exerting force against;
Re = Effective Radius of clamping force.
The fixed caliper works exactly the same way, each bank of pistons is providing the same amount of force. That doesn't double the force, it applies the
SAME force to
BOTH pads. So, you only consider half of the caliper, but double the coefficient of friction.
Here's a better explanation of why that works like that
https://enderw88.wordpress.com/automotive-theory/brake-system-theory/
"Matched properly it would be better to have a larger bore." Why, so you've got more fluid in the caliper to boil? Total system leverage is total system leverage. It scales up and down. Only advantage to bigger pistons in a slider is then you can use a longer pad for more pad service life and properly be able to support it.
What, having a better service life is a bad thing? And yes, actually, having more fluid in the caliper to boil IS an advantage. It takes longer to heat up a larger volume of fluid. And, that larger volume of fluid will likely have a larger surface area with which to transfer heat back the environment. And if you scale the master cylinder to maintain the total system leverage, you haven't lost anything from a braking perspective, and might even have gained some improved fade resistance. Yes, that's
definitely splitting hairs.
You don't have to be a thermo genius to design brakes, they aren't that complicated. "Rudimentary" is your term, not mine. Brake fade resistance at the rotor is a function of how much CFM goes thru the rotors. Width of the rotor is just one factor in that. It is a big one, but it's not the only one.
Right, your term was "basic", rudimentary is a synonym. Brake fade resistance also isn't the only advantage of a thicker rotor. And yes, there are other factors, but they generally favor thicker rotors, not thinner.
As far as being a "thermo genius", no it's not necessary. But considering that generating heat is what a brake does, and the ability to exchange that heat to the air determines how well your brakes will continue to work, I don't see why you wouldn't want to be, or have, a "thermo genius" on hand to improve your design. The more efficiently a set of brakes dissipates heat the better they will be.
