Girodisc Rotor Construction
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.
A note on drilled discs:
Girodisc does not recommend drilled discs for
high performance applications. The rapid heating and cooling cycles
will cause cracking on the friction surface of a drilled disc. The use
of high friction or racing pads will exaggerate this condition. Most pad
manufacturers specifically recommend that their race pads not be used
on a drilled disc for this reason. Girodisc can drill discs for an
additional fee, if the customer is aware of the potential hazards of
drilling the discs.
Note as example the cracking in this OE Ferrari 550 drilled disc after one track day. Also note this custom front disc of a
Porsche 993 Turbo after hard use.
| 
|
OE Ferrari 550 drilled disc showing cracks after one track event
| Drilled disc showing cracks after one weekend of hard track use |
Q: Should new discs and pads be bedded in and if so, how?
A:
The answer is yes, for optimum performance, any time different friction
materials or discs are introduced, a bedding procedure should be
carried out. Refer to procedure.
Q: Which direction should the discs rotate?
A:
For maximum airflow and superior cooling, the Girodisc system uses
curved vanes. For a curved vane internally vented disc, the geometry of
the vanes dictates the direction of rotation. A curved vane disc must be
installed with the vanes running back from the inside to outside
diameters in the direction of rotation. Your discs will come with labels
indicating their correct placement on the vehicle. Orienting the disc
in this manner creates a centrifugal pump. The rotation of the disc
causes air to be pumped from the center of the disc, through the vanes,
and out through the outside diameter of the disc. This greatly enhances
the disc’s ability to dissipate heat. Discs installed backwards have very limited cooling.
