Brake Rotor FAQ (frequently asked questions)

 

WHAT IS A "FLOATING" ROTOR?

The floating, or castellated dog-drive rotor , is allowed to actually move on the drive flange or hub to which it is mounted. How is this possible? By machining 12 through slots on the inside diameter of the rotor, we can now retain the rotor with separate T-locks or dog-drives. These T-locks fit the width of the slot with a slight clearance, but fit the thickness of the slot with a .020-.030" clearance allowing the rotor to move in , out, and radially. This allows the rotor to remain perfectly parallel with the brake pads at all times, eliminating the effect of spindle or strut flex while under severe braking or cornering (i.e. turning into a corner with the brakes still on). This system most certainly helps driver "feel" for brake modulation, along with reduced "pad taper" and rotor wear . A cooler running brake rotor is also attained relative to a non-floating type. For a track only or race car, the floating rotor is the way to go. It's really only necessary in the front but has been used on all four corners on some serious race cars (Formula-1, GT,ALMS). However please be aware that a floater can make a slight knocking noise at low speeds, so they can be annoying for street use.
 

WHAT IS A "NON-FLOATING" ROTOR?

A non-floater is the traditional type of rotor, and its operation is pretty self explanatory. It does not move independently from its mounting flange or hub. When the spindle or strut flexes under severe conditions, the rotor moves right along with it, allowing it to become slightly cocked relative to the brake pad. This promotes small amounts of pad taper and a hotter running brake rotor. However, this is the recommended rotor for the street , or combination street / lite track car. It is still an excellent rotor because of the quality of the casting, the heat treating and shear heat sink mass.
 

DRILLED VS SLOTTED

The drilled rotor so common on the Porsche 930 turbo is NOT really drilled at all. It is a CAST hole. Porsche did this to help minimize the effects a hole has in creating a stress riser in the surface of the brake rotor. A drilled hole goes directly through and interrupts the grain structure of the metal. Where as a cast hole has the grain structure formed around it in an uninterrupted flow. All holes in a brake rotor will eventually show signs of stress cracking. A drilled hole will crack much sooner than a cast one. Admittedly, a "drilled" rotor will cool better than a smooth rotor, and has slightly better "bite". However, the person who blindly goes ahead and drills his stock rotors is asking for trouble, especially in high heat or severe brake conditions (e.g. 944 Turbo's). It's not unusual for these rotors to eventually crack completely across the surface, causing a dangerous situation. Therefore, it is not recommended to drill unless it is an under-stressed condition (i.e. a 2500lb car with Turbo or "S-4" brakes) or, for a street car just for looks. The best compromise for serious track people who don't want to replace their rotors every season is to go with a "slotted" or gas vent rotor. These vents can be machined in various configurations. A ball shaped cutter is used to prevent any stress risers. The purpose of these vents is the same as the cast holes: to give gases, water, and other dirt a place to go under hard braking. This is the most durable track or race rotor. In general, we recommend drilling our race rotors when the car is under 2600 lbs.
 

WHAT IS HEAT TREATING / STRESS RELIEVING?

Any manufactured part has some built in internal stress and brake rotors are no exception. If you were to cut through a brake rotor ,from outside dia. to inside dia., the built up stress would spread the opening many times greater than the width of the saw blade used to cut it. This stress is the kind of thing that we are trying to "normalize" by bedding in new brake rotors on the track. Doing this properly is lucky at best. This process is what warps most new rotors the first few times their used. The most effective way to normalize these stresses is to do it in the controlled environment of a heat treating oven. First the heat is applied gradually to the optimum temperature then cooled slowly while left in the oven. All this is done in an "as cast" condition before any machining is done so as to not affect the final dimensions of the rotor. The final machining is then done and you're left with an unstressed brake rotor ready for the track.

HAPPY BRAKING!!