ARE CROSS-DRILLED AND SLOTTED ROTORS HARD ON BRAKE PADS?

A more powerful engine uses more fuel, and it stands to reason that if brakes do more work, or generate more energy, they must suffer more wear. In the original planning stage we predicted a 10 per cent increase in pad wear. After all, the holes and slots would be abrasive on the pads and, with less metal-to-pad friction area, we expected more rotor wear too.

Yet the on-road results have surprised us. In normal usage, pad wear is generally no greater, and rotor wear is sometimes extended.
Testing on high-mileage taxis has shown a totally unexpected benefit. One leading taxi company using DBA Street Series rotors on its fleet has reported that they can last up to 150,000km with no machining.

This is three times the company norm, and has been achieved without any additional pad wear (the pads continue to be changed at the normal 25,000km intervals).

The reason for the improvement relates to the shaving effect of the slots, which ensure improved contact between pad and rotors, plus the lower running temperatures. Should high-mileage DBA Street Series rotors require machining, this must be performed on a modern, high-speed, low-feed brake lathe. The correct procedure is for the technician to machine from the hub to the outer edge, taking 0.25mm (.001’) in each pass.

A word of caution: machine in the one direction only: when feeding back, the technician should withdraw the tools and recommence from the hub to avoid tip damage and repeat until required finish is achieved. Cross-drilling and slotting remove not only weight but also friction surface (or ‘swept’ area). The figures are relatively small and the enhanced performance shows that the reduction in swept area is more than made up for by the improved ventilation that cross-drilling and slotting achieves.

For the record, the four disc rotors on a typical big sedan have a total swept area of 351.5cm2. The cross-drilling on a DBA Gold rotor removes 22.9cm2, while the slots take away another 5.4cm2. That’s a total of 28.3cm2, or 8.1 per cent of the surface area.