Discs essentially take the kinetic energy of the vehicle and
utilising friction turn this into heat energy stored inside the
disc. This energy then needs to be dissipated sufficiently
before the next amount of kinetic energy needs to be absorbed.
Ventilating the disc internally with vanes helps, these vanes
are often curved to assist with airflow from the inside of the
spinning disc through to the outside edge. The greater the
airflow, the faster the disc will cool. The heating and cooling
process is called the thermal cycle, and it is important to have
a disc of sufficient mass (weight) to be able to absorb all the
heat required and cool down again within the capacity of the
disc. If the disc is too light, the disc will get too hot, then
cool down again, then get too hot again, and so on until the
disc cracks because the thermal cycle exceeded the capacity of
the disc. A heavier disc will absorb the same amount of energy
and not get so hot, thereby reducing the thermal cycle, and the
disc will last. All too often light discs are mistakenly chosen,
and they will fail prematurely, usually warping before cracking.
Discs are oddly one area of un-sprung mass that does need to
have weight to some degree.
However, the part of the disc that needs to have mass is the
part that comes into contact with the pads, rather than the
central mounting bell part of the disc. This is why the bell
part of the disc is often aluminium (which is not only light but
dissipates heat extremely well). The problem with aluminium is
that when heated, it expands at a greater rate than steel. When
the bell is rigidly bolted to the disc, the differential rate of
expansion can cause issues like warping and cracking. Allowing
the two metals to slide against each other alleviates this. This
is why serious racing discs allow the disc to float on the
driving bell. This type of disc location also allows the disc to
self centre, which will reduce pad knock-off (where the pads are
pushed away from the disc by the disc not running true).
Nitron Design
Nitron offer several
fully floating disc and bell combinations
utilising the best materials available. Our disc kits utilise a
bobbin drive system, where a series of Titanium bobbins are
bolted to the disc and then the aluminium bell has a number of
slots machined into it where the bobbins slide as the bell
expands. The bells are machined from 7075-T6 aluminium and then
hard anodised to provide a super stiff bell with a very hard and
durable coating. The bells are then laser etched with their
details. The following sizes are available:
• 304mm OD x 25.4mm thick 12 bobbin drive
• 295mm OD x 25.4mm thick 12 bobbin drive
• 290mm OD x 25.4mm thick 8 bobbin drive
Note: the 290mm disc can be used with the standard hand-brake
caliper on the rear. All discs can be used as front or rear
discs on cars with 4 bolts on a 100mm PCD, i.e. Elise S2
onwards.
