GiroDisc Porsche 911 GT3 Cup (991) Slotted Rear Rotors

GiroDisc Porsche 911 GT3 Cup (991) Slotted Rear RotorsSold priced in pairs Welcome to GiroDisc! Brake rotors have long been the overlooked link in performance car braking systems. Traditional 1 piece brake rotors are heavy and retain heat, diminishing their effectiveness and adding unsprung weight that adversely affects handling. When GiroDisc was founded in 2003, we made it our mission to design and manufacture 2 piece brake rotors that would perform flawlessly at the limits. Our fully floating design

Sold/priced in pairs


Welcome to GiroDisc!

Brake rotors have long been the overlooked link in performance car braking systems. Traditional 1-piece brake rotors are heavy and retain heat, diminishing their effectiveness and adding unsprung weight that adversely affects handling.

When GiroDisc was founded in 2003, we made it our mission to design and manufacture 2-piece brake rotors that would perform flawlessly at the limits. Our fully-floating design uses tension hardware to ensure that our rotors are silent on the street, but ready to go on the track.

By specializing in this area, we can dedicate our efforts to push our engineering and manufacturing to the highest levels in the industry. Customers around the world have found success maximizing the capabilities of their existing brake systems by installing GiroDisc rotors. This often negates the need for a pricier, more complex upgrade like a big brake kit.

GiroDisc is headquartered in Bellingham, Washington, where we design, engineer, manufacture and fulfill orders on site.

The primary purpose of the Girodisc system is to reduce unsprung and overall vehicle weight. The secondary purpose is to increase the ventilation and cooling capacity of the brake disc while retaining it's original dimensions. This is accomplished by using two-piece disc construction. The central hat section of the disc is made from 6061-T6 aircraft specification aluminum.

The disc is made from cast iron, to the same specification and material as used by professional racing organizations. It is a curved vane design, developed in racing to act as a centrifugal pump to force cooling air through the disc. The rotor and hat have a floating mount system, which utilizes high strength alloy steel drive pins, manufactured by Girodisc to our own specifications and cadmium plated for a long lasting corrosion resistance. These pins take the load from braking actions while maintaining the axial and radial float between the hat and disc. The pins are secured by grade 12 cap screws with hardened washers. In order to keep the rotors from making noise when cold, the pins are mounted with anti-noise spring clips on the rotor side which allow the rotor to grow with heat expansion but eliminate the rattle and noise associated with floating rotors. This float also allows the rotor
to self center between the pads.

Important Questions Answered

Q: What is required to install the Girodisc system?

A: The Girodisc system is a direct replacement for the OE disc.
No modifications are necessary. The disc will bolt directly to the car and work with OE calipers and pads perfectly. Once the Girodisc system is in place, simply replace the cast iron rotor when needed. Some discs are larger in diameter and come with caliper spacers. If longer bolts are required, they are also supplied.

Q: How does reducing weight of the braking system benefit the vehicle?
A: The Girodisc will generally weigh between 4 8 lbs less than the oe disc it will replace. This is due to the heavy cast iron hat section being replaced with lightweight, high strength aluminum. The mass of any vehicle requires energy to accelerate or decelerate. Reducing the vehicle mass improves acceleration, and requires less energy to be dissipated during deceleration. Rotating mass requires additional energy in order to increase or decrease its speed of rotation. Decreasing the mass of the disc has a great benefit due to reduction in rotational inertia. This will allow more of the braking force to be available to decelerate the vehicle, not the disc.
Additionally, the mass of the brake system is also unsprung mass. Reducing the unsprung mass has the additional benefit of improved suspension performance, resulting in enhanced ride and handling. Rotating masses require additional energy to vary the plane on which they turn. The lighter the disc, the quicker the response of the vehicle steering due to the reduction in gyroscopic effect/rotational inertia of the disc. As an example, compare the weight of the Ferrari 360 OE disc at 18.2 lbs, and the Girodisc at 14 lbs. The Girodisc is 4.2 lbs lighter per disc. Replacing all four discs will save 16.8 lbs of rotating, unsprung mass.

Q: Why slotted discs?
A: The edges of the slots continuously clean and refresh the pad surface. This will allow the pads to have a maximized friction surface always available. Additionally, they prevent containments from collecting between the pad and disc interface.
The disc is lightened, decreasing its rotational inertia.
Slots prevent the formation of a water film on the disc in wet weather, maintaining the best brake response.