The StopTech two-piece rotor uses a differential curved vane rotor design. The offset long
Rotors
Rotors are the spinning part of the brakes that the calipers and brake pads clamp onto. In addition to providing a friction surface, the rotor's main role is to pump away heat generated through braking because it experiences the highest temperatures. Most rotors are sand-cast from gray iron of various qualities and have an air gap between the two rotor faces. The air gap (commonly referred to as a vented rotor) allows air to move through the rotor and pull away heat. Solid rotors also exist, typically on the rear brakes of non-performance platforms. Several designs exist for the vents, but most can be broken down to directional or non-directional categories. As the name suggests, non-directional (aka straight vane) rotors can rotate in either direction and still provide venting, although not as effectively. Stock factory brakes and lower-end replacement rotors use this design because the same part can be used on both sides of the car. A take-off of the straight vane design is the pillar vane design that is better at maintaining a smooth, consistent friction surface.
Directional or curved vane rotors only cool effectively when rotating in the right direction but are far more efficient at moving cooling air through the rotor. Most high-performance applications and race rotors (with the exception of carbon/carbon rotors) use curved vane rotors. A directional vane rotor upgrade on cars like the EVO, Z or STi are a simple but hugely effective choice. Our StopTech rotors use a patented variation of the curved vane design called Aerorotor with alternating differential curved vane lengths to further increase cooling effectiveness. To maintain rotor strength, slots and drills in curved vane rotors are typically machined in the opposite sweeping direction than the vanes so that a slot doesn't occur directly on top of a vane or a hole drilled through it.
Fixed Or Floating Rotors
A further step in upgrading rotors is to use a two-piece or floating design. (Don't be fooled by single-piece rotors with painted black hubs and fake rotor bolts.) Real floating rotors have reduced weight, rotational inertia, heat transfer to the wheel bearing, rotor deformation and knockback effects. The trade-off is obviously a much higher price, which is why these rotors only show up on stock vehicles like Ferraris, GT-Rs and the EVO X MR.
By using an aluminum hat that's semi-solidly attached to the rotor, a true floating rotor allows the rotor to expand and contract radially as heat is increased. Slotted mounting holes machined in the rotor friction disc allow the rotor to grow without stretching and deforming the hat. The two pieces are attached using drive pins, Belville washers made from Inconel and bolts that allow the rotor to expand and contract concentrically through heat cycles, but stay in-plane with the hub to reduce noise. The total amount of float is controlled by a strictly held tolerance on the drive pin length and the Belville washer design. Two-piece rotors when used in racing are designed to have axial float, which allows the rotor to slightly wobble as if you have a bad wheel bearing. Under race conditions, axial float allows the rotor to better align to the caliper and pads as it spins, which helps reduce knockback. Too much axial float is bad on a street car because it makes all kinds of noise. To keep the street/track balance, StopTech assembles the Trophy Sport rotors to have less float than the race-spec rotors.