SmackDaddy
03-16-2006, 04:44 PM
...that posting on corner-carvers is dangerous!
taken from: http://www.corner-carvers.com/forums/showthread.php?t=14827&page=3&pp=40
______________________
Finally, a few comments regarding brake system fundamentals.
1. As has been stated already on this thread, the tire stops the car. Period. The force developed at the contact patch is the only force which can decelerate a vehicle, aero effects and road grade not withstanding.
Naturally, it is up to the braking system to utilize the four contact patch forces to their maximum for the entire braking event. On vehicles without ABS, this is largely a function of bias. On vehicles with ABS, bias mismatches can be accommodated to a certain point.
In all cases, brake system response time and efficiency can influence the time to achieve initial deceleration. Consequently, more efficient (stiffer) brakes can influence stopping distance to a small degree. On the street, this is probably negligible, but on track it can make a difference. Of course, braking five feet later might not matter to you, but it does to people who drive race cars for a living.
2. Braking “power” is not a valid concept when discussing deceleration. Vehicles decelerate because of linear forces generated at the contact patch. These forces exist because the tire is slipping relative to the road. The tire is slipping because the brake is applying a constant torque to the rotating assembly. T (torque) = I (inertia) * alpha (rotational acceleration). One can certainly calculate the total power consumed during the braking event, but it does not factor into the deceleration equation kinematics.
Rotational speed of the rotor as it passes the brake pad also does not factor into the deceleration equation kinematics. Certainly, the higher the rotational speed the higher the inertia of the rotating assembly, but that simply changes the acceleration reaction of the spinning mass. It does not change actual brake output. It just means that the same output may have a smaller acceleration reaction which results in less force at the contact patch under dynamic conditions. Once steady-state has been achieved, the term goes away altogether.
All of the talk around “brake power,” “swept area,” and “pad geometry” influence the dynamics of the heat transfer function. There is no impact to the vehicle deceleration reaction.
3. Increasing rotor diameter will increase brake output. This will reduce partial braking (non-limit) stopping distances. Decreasing rolling radius will also decrease partial braking distances. Increasing piston area or coefficient of friction will also decrease partial braking stopping distances. This is because all of these parameters determine the brake system gain, or brake pedal force-to-deceleration relationship up to the point of tire peak traction.
While all of these factors will decrease partial braking stopping distance, the shortest stopping distance is still a function of tire tractive capability. For the plain-English talk of how this all factors together, you can surf here:
http://www.teamscr.com/grmbrakes.html
__________________________
Anyone have a different opinion or can add to this discussion regarding brakes?
taken from: http://www.corner-carvers.com/forums/showthread.php?t=14827&page=3&pp=40
______________________
Finally, a few comments regarding brake system fundamentals.
1. As has been stated already on this thread, the tire stops the car. Period. The force developed at the contact patch is the only force which can decelerate a vehicle, aero effects and road grade not withstanding.
Naturally, it is up to the braking system to utilize the four contact patch forces to their maximum for the entire braking event. On vehicles without ABS, this is largely a function of bias. On vehicles with ABS, bias mismatches can be accommodated to a certain point.
In all cases, brake system response time and efficiency can influence the time to achieve initial deceleration. Consequently, more efficient (stiffer) brakes can influence stopping distance to a small degree. On the street, this is probably negligible, but on track it can make a difference. Of course, braking five feet later might not matter to you, but it does to people who drive race cars for a living.
2. Braking “power” is not a valid concept when discussing deceleration. Vehicles decelerate because of linear forces generated at the contact patch. These forces exist because the tire is slipping relative to the road. The tire is slipping because the brake is applying a constant torque to the rotating assembly. T (torque) = I (inertia) * alpha (rotational acceleration). One can certainly calculate the total power consumed during the braking event, but it does not factor into the deceleration equation kinematics.
Rotational speed of the rotor as it passes the brake pad also does not factor into the deceleration equation kinematics. Certainly, the higher the rotational speed the higher the inertia of the rotating assembly, but that simply changes the acceleration reaction of the spinning mass. It does not change actual brake output. It just means that the same output may have a smaller acceleration reaction which results in less force at the contact patch under dynamic conditions. Once steady-state has been achieved, the term goes away altogether.
All of the talk around “brake power,” “swept area,” and “pad geometry” influence the dynamics of the heat transfer function. There is no impact to the vehicle deceleration reaction.
3. Increasing rotor diameter will increase brake output. This will reduce partial braking (non-limit) stopping distances. Decreasing rolling radius will also decrease partial braking distances. Increasing piston area or coefficient of friction will also decrease partial braking stopping distances. This is because all of these parameters determine the brake system gain, or brake pedal force-to-deceleration relationship up to the point of tire peak traction.
While all of these factors will decrease partial braking stopping distance, the shortest stopping distance is still a function of tire tractive capability. For the plain-English talk of how this all factors together, you can surf here:
http://www.teamscr.com/grmbrakes.html
__________________________
Anyone have a different opinion or can add to this discussion regarding brakes?