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Old 03-01-2011, 03:15 AM   #1
mndude07
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Learn About Brakes!

I'm realizing there's not alot of good explanation about brakes here, so I wrote this and will add more indefinitely.

You can only stop as well as your tires will let you, as they are your contact patch with the ground. If you're locking up the brakes with a stock brake setup, you need better tires. Upgrading your brakes will be pointless otherwise.

~Calipers~

There are two types of calipers: fixed and floating. Floating calipers are the OEM style and they slide on the caliper bracket slide pins. Fixed calipers are your Spoon, Brembo, Wilwood, etc. calipers. These are centered over the brake disc and do not move at all. This allows more force to be transferred through the caliper pistons.

The number of pistons a caliper has doesn't directly influence braking power. So, before you just assume that a caliper with more pistons is better, stop and measure the piston diameters. Then, use the formula for the area of a circle to find the total piston area of the caliper. The greater the caliper piston area, the greater the force it can apply assuming a constant line pressure. This is because Pressure = Force/Area, so by re-arranging you can clearly see that if you keep pressure constant, and increase the piston area, the force is greater. Don't forget that formula. It applies everywhere for brakes.

~Rotors~

A larger rotor of course is going to give you more stopping power. But do you know why? The answer is torque. Torque is a force multiplied by a lever arm. The lever arm in the case of a brake rotor for all intents and purposes is the radius, or half the diameter of the rotor, and the force applied is the force applied by the caliper. So, you increase the lever arm, and you increase the brake torque.

One thing to keep in mind, is that a larger rotor is also heavier, and increasing that mass has negative effects in two ways. One, the brake rotor is unsprung mass, so a heavier rotor is going to increase ride harshness. Also, since the rotor has to spin, its inertia is fighting against the engine. Think about what happens when you install a lightweight flywheel. So, depending on your application, you need to find the best of both worlds for braking power and low weight. Increasing rotor diameter isn't the only way to increase braking power though, so maybe stock sized rotors with huge calipers would be a good way to go.....

About different types of rotors...

You have blank, slotted, and drilled.

On slotted and drilled rotors: These are misleading for several reasons. Drilled rotors can be beneficial, but no one in the tuner world seems to use them properly. Companies advertise that drilled rotors help cool your brakes down and reduce brake fade....well that's part of it, but it works the other way too. Your brakes don't work very well if they're too cold either. Drilling rotors is done for thermal mass control and weight reduction. The less material the rotor contains, the faster it will heat up and cool down. This gets your brakes hot faster, but it causes alot of heat cycling as well, which can warp or crack the rotors. Also, with drilled rotors, stress concentrations are an issue. For some reason, alot of tuner drilled rotors have very small holes, and the smaller the holes, the higher the stress concentration...I don't know why they do this. I like to think about brake pads and drilled rotors like those old play-doh extruders. If you squish the pad up against all those holes, its going to squeeze through and then get sheared off repeatedly...this hurts pad life, but helps bite. Slotted rotors are an attempt to keep the surface cleaner without the stress concentration issues. Blank rotors have the most surface area exposed to the pad (a hole in a drilled rotor is a small amount of missing surface area), you don't get the bad pad wear, you don't have to worry about heat cycling, the blanks can take more heat in, and you don't have stress cracks to worry about. That said, I think slotted only is the best of both worlds for a rotor. Its a little lighter, can help remove debris, but you don't need to worry about cracking.


~Brake Master Cylinders~

Its a common misconception that a larger master cylinder is "better". In this case, "better" is a subjective term because it depends on what you want really. The pressure formula applies here too. Pressure = Force/Area. Pressure is the line pressure generated by the master, force is the force applied on the master with your foot on the pedal, and area is the cross-sectional area of the master cylinder bore. So, you can see that a smaller diameter master cylinder actually will provide a higher line pressure, keeping pedal force constant. So, if a smaller master cylinder gives more braking force, what's the drawback? Pedal travel. A smaller master will give a greater line pressure, but you will have to push the pedal further; not harder, don't get them confused. Going too small, the master won't have enough displacement to full extend the pistons in the caliper. Alot of race drivers will prefer a smaller master though because it allows you to modulate the pedal more at the limit, and the track is predictable.

A larger master will require you to press the pedal harder, but you won't have to press the pedal as far. Some people like this because it gives the brakes a seemingly quicker response, which is sometimes mistaken for more braking power.

~Pads~

There are alot of different compounds of pads out there, but two of the most important things to pay attention to are coefficient of friction, and temperature.

The higher the coefficient of friction, the more "bite" the pad has. However, most pads don't have a constant CoF, it varies with pad temperature. So, if you aren't even getting your brakes up to the temp at which the highest CoF occurs, you might want to think about switching pads, or finding a way to heat the brakes faster. How do you tell? Expensive temperature sensors or expensive paint that goes on the rotors. Street pads are obviously designed for typical street temps, so you don't have to worry much.

These are just things off the top of my head, feel free to talk about all the stuff I missed like slotted/drilled rotors, 2 piece rotors, monoblock/twinblock calipers, brake line upgrades, proportioning valves, ABS, brake ducts, bias bars, dual masters, brake boosters, etc, etc, etc

~Brake lines and Fluid~

On upgrading brake lines, inherent swell is only one small part of what they help. Upgrading your lines will not directly help the car stop better, but they do improve pedal feel significantly. When you are driving the car normally and the brakes are at an average temperature, they won't feel any different than stock really. However, if you start getting hotter and heavier braking (spirited driving, canyon runs, back-roading, on the track, etc), the lines are more likely to help you out. SS lines can also handle much higher line pressures, which helps out if you're running a small master cylinder. Safety is another reason as well. SS lines aren't going to succumb to abbrasion, heat, and debris found in the wheel arch area as well, making the chance of failure much less. Also, if you somehow manage to boil your brake fluid, SS lines won't rupture like rubber lines can.

As far as brake fluid goes, you are typically given two boiling points for the brake fluid: Wet boiling point, and dry boiling point. Brake fluid will absorb moisture over time, usually up to about 5%, and when the fluid has absorbed moisture, it is considered "wet". New fluid, of course is considered "dry". Some companies package their fluid with inert gas to keep out moisture while it sits on the shelf. If you are changing brake fluid every time you go to the track or for some other reason, your fluid likely hasn't absorbed much or any moisture, and so the dry boiling point is the most relevant to you. However, 99% of us don't change our fluid that often, so you just assume that your fluid has absorbed some moisture and then you pay attention to the wet boiling point. The wet boiling point is of course lower, so you're effectively creating a factor of safety there for yourself as well. For track use and even just general safety, having the highest wet boiling point fluid possible is what you want.
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Last edited by mndude07; 04-29-2011 at 03:19 AM.
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