Posted by Bill Bowes on January 19, 2003 at 12:12:59 from 24.51.221.8
In Reply to: Brake Upgrades posted by JR --- 1978 635CSi on January 18, 2003 at 17:27:32:
The only better brakes I've come across, other than the brembo's are on the 745i. The discs are thicker, as are the calipers. The only problem is that they were made for ABS, and they only have one brake line. This would make a swap a tad difficult.
Brakes are one of the most mis-understood items on our cars. And it seems the younger the person, the less is understood. I know. i have a teenage son who either knows everything or his friends do.
Contrary to what most people think, crossdrilled and or slotted rotors do NOT make your brakes better. Indeed, they may make them worse, and more dangerous.
Think about this. Brakes work based on friction. The more friction you have, the faster you stop. The less friction you have, the longer it takes to stop. And what happened when you crossdrilled or slotted those rotors? You removed surface material, which reduced the amount of friction.
So why have crossdrilled/slotted rotors? Heat is the enemy of friction. As the temperature of the brake materials increases, the harder it is to obtain the necessary friction to stop. The holes and slots help dissipate heat. Harder pad materials, including more metal content which can stand the heat help to handle the heat. On race cars, there are ducts built into the car body which tunnel air directly onto the calipers to cool things down.
All this heat stuff sounds like it'd be a great upgrade, right? For track use, yes. For the street, no.
Crossdrilled/slotted rotors will help dissipate heat, but you will never EVER get to the point where they'd actually be of use on the street. You simply do not use the brakes on the street, the way they are used on the track.
On the street, you come to a leisurely stop at a light or stop sign. On the track, you use threshold braking, which means come in to the turn at speed, and wait until the last moment, and hit the brakes hard just to the point that they'll lock up. Do this on the street, and you won't be driving long.
Even if you make your street stopping decisions late and have to nail the brakes hard, it's nothing for the E-12's stock brakes. Sure they get a bit hot, but this type of stopping is unlikely to be sustained, and they are designed to take this type of abuse (I used completely STOCK pads and rotors on a 2002 at a driving school at Sebring. They lasted 2 days worth of sessions. They were toast at the end, but they took it).
In a panic situation on the street, you'll want all the braking surface you can get.
On the track, you'll be stopping and slowing hard every 10-20 seconds. Suddenly, heat dissipation is much more important than braking surface. If your pads fade because your rotor is glowing hot, the next stop will be against the tire wall.
While we're on the subject of pads. Racing pads should not be used on the street. They are designed to work optimally at high heat levels. You'll NEVER attain these levels on the street. If you want to spend $$, you can get pads with more metalic content, but you'll probably only use up your rotors sooner. And your cross drilled rotors will use up your pads sooner too. Also, I have used two sets of Zimmerman rear crossdrilled rotors on the back of my 325i. After two driving schools, and street use (I was too lazy to changed them) both sets cracked. Luckily, I found them before the rotors completely broke.
So what upgrades ARE good for the street? I like ATE Blue fluid. Change it at least once a year. Stainless brake lines are also a good upgrade. Anyone who hasn't changed out their brake lines should do this. One of the main causes of pulling to one side is the rubber lines being blocked or shot.
And if you want a real project that will do the most to improve your brakes over all, take the ABS off an E-28 and put them on your E-12. That would be an upgrade.