mazdaexe

Hi, can someone educate me on braking systems?

1. Cross drilled or Slotted or both
What are the pros and cons of each? I heard that drilled rotors releases the heat better than slotted, but drilled rotors are weaker and easier to break?

2. 6-piston vs 4-piston
Rotora is offering a big brake kit with 6-piston calipers and stoptech is only offering 4-piston. I assume that the more pistons the better.

Thanx!

rabinabo

1. http://www.ffcobra.com/FAQ/brakes3.html
http://stoptech.com/technical/

2. More pistons means that the calipers perform better, but overall it may throw off the balance of the whole brake system if you don't also upgrade the rear brakes.

syntrix

Depends on the casting for drilled, if it's stock, or oem like, it can cause weakness.

I'm a firm believer in slotted, especially on the track, but either way, your pads are going wear faster! The best advantage is if you actually experience brake fade on the track.

I experienced 0 brake fade on the track at stock suspension, stock power, and just upgraded 245 tires.

Depends on what you want to do. But slotted/drilled do look cool on the car! But are they really helping? hehe

Sputnik

Not necessarilly. When comparing two calipers, you have to consider the piston area. Just like all else being equal, a 4.0L V8 isn't going to be more powerful than a 4.0L V6. Alot of these 6-piston jobs for the street have little to no more piston area than a good 4-piston job. But like the 4.0L V6 vs. 4.0L V8 comparison, there are pluses and minuses for both, and proponents of each.

---jps

DZeckhausen

Drilling rotors has nothing to do with heat dissipation. Those that claim otherwise are trying to separate you from your money! There are three mechanisms for removing heat from a rotor and they are radiation, convection, and conduction.[list=1][*]Radiation is a function of the total surface area and the temperature difference between the rotors and the air. On a typical car at the track (without ducting that forces air into the center of the rotor) the contribution of radiation to overall cooling is about 50 percent.
[*]Convection is a function of the airflow through the rotor and is a function of the air gap between the two friction surfaces and the design of the internal vanes. Convection contributes about 25 percent of the overall cooling. Drilling holes perpendicular to the direction of airflow does nothing to help cool the rotors. In fact, the reduced mass of drilled rotors means they will be hotter at the end of a given stop than non-drilled rotors, all else being equal.
[*]Conduction is when heat is transferred into your wheel bearings or through your pads and pistons into the brake fluid. Conduction is bad and should be minimized, if possible. Conduction contributes about 25 percent to the overall cooling.[/list=1]
Slotting and drilling both provide the same benefits of slightly increased bite and a place for pad gasses to escape during the "green fade" of initial pad break-in. However, slotting doesn't have the disadvantage of drilling, which is the propensity to crack sooner, due to the stress risers at the edges of the drilled holes. Chamfering the holes helps reduce stress, as does reinforcing the rotors at the points where the holes are to be drilled. However, even the wonderful Porsche rotors (drilled rotors done right) will crack more quickly at the track than good quality plain or slotted rotors.

Nope. The number of pistons has nothing to do with the quality of brake system. What is critical is the overall piston area. That determines how much brake torque is applied. A larger piston count allows you to design a pad with a larger surface area and the multiple pistons keep the pad from distorting by applying pressure evenly across the backing plate. A small caliper with lots of pistons is simply a marketing ploy to take advantage of the meaningless "piston wars" that vendors are starting to get into. What is critical is the balance of a system. You want to make sure the front brakes don't lock up prematurely so that the rear brakes can do their fair share of the work. Some vendors just throw large calipers at a car and hope that ABS will sort out the balance problem for them. This doesn't work and it results in longer stops, not shorter.

Last December, I participated in a track testing session with StopTech and I kept a diary which I subsequently put onto my website. You might find it interesting and educational: http://www.zeckhausen.com/Testing_Brakes.htm. At the time, I was NOT a StopTech vendor. Since that time, I started a business that includes several brake manufactureres including Brembo and StopTech. But when I wrote my account of that testing day, I had no financial interest in StopTech.

DZeckhausen

Actually, the addition of two more pistons dramatically weakens the caliper, causing it to deflect more under pressure. StopTech has done exhaustive caliper deflection testing and the results consistantly show that a 6-piston caliper exhibits much more flex than a 4-piston caliper from the same manufacturer. You can check out their deflection charts here: http://www.stoptech.com/technical/ca...ctionchart.htm

The "performance" of a caliper consists of a number of factors, including clamping force (a function of total piston area), caliper stiffness (which translates into pedal firmness and more even pad wear), and ability to withstand multiple heat cycles (function of material used and physical design).

For example, Brembo and StopTech calipers can last many seasons without experiencing a degradation in stiffness, whereas some of the cheaper Wilwood calipers lose much of their rigidity after just a couple of races and are often replaced.

Roar 629

i have a similar question, i know that rx8 come with almost an inch larger diamater rotor than the FD's 11.6, i've a friend that wish to swap the FD caliper to the 8, any advice to him?

PUR NRG

Hi Dave, nice to see you on this forum.

Shameless endorsement: for those unfamilar with Dave Z, he's an overall nice guy. Back when I was a newbie to the world of modding he helped me and countless others--often for free. Now that he's running his own business I encourage people to buy from him whenever possible.
________
Maryjane

Kwullen

Dave,
Do you have a higher quality replacement rotor available for the 8?

shelleys_man_06

I love your technical nerdisms Dave . It's so refreshing to find a post containing the basic mechanisms of heat transfer .

DZeckhausen

What do you mean by "higher quality" replacement rotor? Do you mean better than stock? Any mainstream brand aftermarket rotor is going to be virtually identical in metallurgy and will have no benefits over the stock ones other than, perhaps, being lower in price. Unless you change the size of the brakes, there will be no improvement in thermal capacity or ability to shed heat. And changing rotor size requires an entire upgrade to the system, including different calipers.

Is there something about the stock rotors that is causing you a problem? Are you experiencing fade? Are you simply looking for a lower cost alternative to replacing worn out rotors? I need a bit more information about what you are trying to accomplish before I can give you any reasonable advice.

ScudRunner

I'm just looking for a rotor that will have a little bit of a protective coating on it so it won't rust as much. So far I have no complaints whatsoever about the stock brake setup (cept maybe the dust), except for the appearance of it.

DZeckhausen

Ah! I get it. The "ring of shame" is bothering you.

I don't have any coated rotors for the RX-8 yet. But you can do it yourself with either high-temperature engine paint (I like Plasticote 1500 degree Hot Paint) or you can use POR-15. Try not to get any on the friction surfaces. And make sure you clean off all the oils before painting the rotors. The manufacturers spray oil on the rotors before boxing them up so they don't rust. Brake cleaning spray gets it right off. Plated rotors are not usually coated with oil, however.