# RE: Brakes

```I don't think you can simply isolate the effectiveness of brakes from the
size/mass of the rotors.  Swept area, coefficient of friction, temperature, etc
all come into play.  In the final analysis it is the ability of the brakes to
convert kinetic energy into heat (with a tiny bit of noise) and in the interest
of repeated uses, dissipate that heat.  A larger diameter rotor will generally
do that more effectively.

As an illustration of the complexity of brake design it is not just size of disc
vs swept area vs Cf but also where all of this interaction takes place on the
disc.  In this case you could have the exact same disk (mass, diameter, etc) the
exact same swept area and the exact same coeffficient of friction, but different
braking effectiveness.  As an example find a turntable (you know the things that
play vinyl discs) and put on something you don't care about.  Put you thumb
(simulated single piston caliper) on the disc somewhere near the edge.  It
should be easy to stop the disc.  Now put your thumb somewhere near the center,
it should be much more difficult to stop.  This is because the longer moment arm
available at the edge of the disc; even though all other factors were the same.

If this isn't good enough you could always get two cars, exactly the same and
play with the brakes.  It gets complicated very fast because even doing
something like changing only to drilled, vented rotors (less mass, less rotating
mass, less swept area) can improve your braking because of improved heat
dissipation and potentially eliminating a very thin layer of gas due to
vaporisation of the brake pads and thus increasing the effective coefficient of
friction.

Joe Yakubik

```