Originally Posted by Trailbraker
Hmm who do I believe, Mr Dong who "works with brakes for a living" or Mr. Brembo who "does brakes for Formula 1 cars@
I really can't believe Porsche would compromise their brake system for aethetics, I mean why bother their cars are tending towords ugly in general, but lovable in an efficient form is function type of way.
Track day and fast road use is very different to actual racing applications where the discs are under more extreme prolonged stress - if there is independently researched data on the heat dissipation characteristics I would be interested to see it.
Can find more reasons not to use drilled than reasons to use drilled
1) Drilled VS Slotted
"For many years most racing rotors were drilled. There were two reasons -
the holes gave the "fireband" boundary layer of gasses and particulate
matter someplace to go and the edges of the holes gave the pad a better
Unfortunately the drilled holes also reduced the thermal capacity of the
discs and served as very effective "stress raisers" significantly
decreasing disc life. Improvements in friction materials have pretty
much made the drilled rotor a thing of the past in racing. Most racing
rotors currently feature a series of tangential slots or channels that
serve the same purpose without the attendant disadvantages.
the process of drilling rotors and slotting rotors was done for 1 reason
and 1 reason only it is to disipate the gases that build up between the
pad and the rotor which occurs under extreme heat ( when braking very
aggressively like on a road course) and it has absolutely nothing to do
with heat disipation. the only way to transfer more heat away is by
using a larger heat sink which means use of a larger rotor whether in
diameter or thickness. Since the caliper will only allow for a certain
rotor thickness that solution is not very applicable because, if you are
changing tha caliper opening width you might as well get a larger rotor
diameter at that time
1) The brakes don't stop the vehicle - the tires do. The brakes slow the
rotation of the wheels and tires. This means that braking distance
measured on a single stop from a highway legal speed or higher is almost
totally dependent upon the stopping ability of the tires in use - which,
in the case of aftermarket advertising, may or may not be the ones
originally fitted to the car by the OE manufacturer.
2) The brakes function by converting the kinetic energy of the car into
thermal energy during deceleration - producing heat, lots of heat -
which must then be transferred into the surroundings and into the air
The amount of heat produced in context with a brake system needs to be
considered with reference to time meaning rate of work done or power.
Looking at only one side of a front brake assembly, the rate of work
done by stopping a 3500-pound car traveling at 100 Mph in eight seconds
is 30,600 calories/sec or 437,100 BTU/hr or is equivalent to 128 kW or
172 Hp. The disc dissipates approximately 80% of this energy. The ratio
of heat transfer among the three mechanisms is dependent on the
operating temperature of the system. The primary difference being the
increasing contribution of radiation as the temperature of the disc
rises. The contribution of the conductive mechanism is also dependent on
the mass of the disc and the attachment designs, with disc used for
racecars being typically lower in mass and fixed by mechanism that are
restrictive to conduction. At 1000oF the ratios on a racing 2-piece
annular disc design are 10% conductive, 45% convective, 45% radiation.
Similarly on a high performance street one-piece design, the ratios are
25% conductive, 25% convective, 50% radiation.
3) Repeated hard stops require both effective heat transfer and adequate
thermal storage capacity within the disc. The more disc surface area per
unit mass and the greater and more efficient the mass flow of air over
and through the disc, the faster the heat will be dissipated and the
more efficient the entire system will be. At the same time, the brake
discs must have enough thermal storage capacity to prevent distortion
and/or cracking from thermal stress until the heat can be dissipated.
This is not particularly important in a single stop but it is crucial in
the case of repeated stops from high speed - whether racing, touring or
4) Control and balance are at least as important as ultimate stopping
power. The objective of the braking system is to utilize the tractive
capacity of all of the tires to the maximum practical extent without
locking a tire. In order to achieve this, the braking force between the
front and rear tires must be nearly optimally proportioned even with ABS
equipped vehicles. At the same time, the required pedal pressure, pedal
travel and pedal firmness must allow efficient modulation by the driver.
5) Braking performance is about more than just brakes. In order for even
the best braking systems to function effectively, tires, suspension and
driving techniques must be optimized"
2) BMW E30
The factory brakes on your E30 may be marginal if you use your car on the track or otherwise drive hard, especially if you have a modified engine. Here is some information about a simple thing you can do - changing brake disks.
The brake disks you can use on your BMW have one of the following surface types:
Solid face. Smooth. Like most brake disks. No holes or grooves of any kind.
Cross-drilled. (holes) You should NEVER drill ordinary disks, even if you know what you're doing (the holes must be chamfered and the disks must be balanced afterwards). The holes will generate thermal stress cracks which can cause the disks to grenade.
Yes, we've seen this on the track. The ONLY acceptable cross-drilled disks are those ORIGINALLY manufactured that way. Or, if absolutely necessary for race cars, you can use them, but they MUST be thrown away at the first sign of tiny cracks coming from the holes.
Gas-slotted. These can be conventional straight slots, or slightly curved ones, or an elaborated pattern as in the ATE Power Disk. These work about as well as the best factory drilled ones, and without the thermal crack problem.
And look at all the arguments and opinions here