http://www.thesamba.com/vw/classifieds/detail.php?id=573200WHAT DOES ‘CROSS-DRILLED AND SLOTTED’ MEAN?
The expression 'cross drilled and slotted' refers to two separate processes, and the enhanced performance versions of DBA Street Series rotors incorporate one (DBA Slotted) or both (DBA Gold).
The first procedure involves drilling holes through the friction surfaces of the rotor and the second refers to milling a series of grooves from the centre of the disc toward the edge. The processes are aimed at making the disc better ventilated and more effective. And let’s not forget the cosmetic side: DBA Street Series rotors look aggressive and purposeful, particularly with today’s open-patterned alloy wheels.
DOES A DISC NEED TO BE CROSS-DRILLED AND SLOTTED?
Not necessarily. The processes achieve slightly different ends.
Let’s talk about cross-drilling first. When the friction surfaces of a rotor are smooth and flat, there is no means of escape for the gases and dust that build up between pad and rotor. At very high braking temperatures, the bonding agents used in some brake pads can produce a gas which creates a pneumatic cushion between pad and rotor, giving a driver a normal pedal feel but reducing the amount of friction being generated. This is not a huge problem in normal motoring but is an important consideration in street performance applications.
The bigger the pads and the higher the braking temperatures, the more likely the problem. The drill holes assist with this 'out gassing'. The holes are also commonly labelled 'cooling holes' because of the improvements they make in this
area. Better cooling means less fade during repeated heavy brake applications.
Obviously, the holes reduce mass. They also help dissipate water when driving in poor weather.
WHAT DOES SLOTTING DO?
Slotting increases the bite of the pads. This helps pull the car up more quickly. Used on its own, the process doesn’t involve removing as much metal as cross-drilling, so it doesn’t result in as great a weight saving. However, slotting can be as effective as cross-drilling in combating the problem of 'outgassing', particularly with the nine uni-directional slots fitted to each side of DBA Slotted rotors. The slots pump away gas and restore full contact.
The 'micro-shaving' effect of the slots also serves to de-glaze the pads (this is why the edges of the slots on DBA Street Series rotors are not chamfered or 'radiused'). It also tends to even out the wear across the brake pad faces, increasing the effective contact area. This can extend rotor life.
