Swept area

[C M Smith <cmsmith@domain.elided>]

I too think brake swept area is not particularly relevant. Road & Track has 
stopped publishing this calculation in part recognizing the irrelevance of 
the number.

Brake torque is pretty significant. Bigger diameter brakes exert more 
leverage due to the radius of the rotor.

Rotor area relative to pad area also makes a big difference in brake 
cooling which can be important if the brakes are used hard and frequently. 
This is mostly irrelevant for street driving with 4 wheel disc brakes. 
Modern brakes do not fade significantly. What's left is mainly brake feel, 
an esthetic experience.

Vented brakes are useful as airflow is by far the most significant factor 
in brake cooling. Cross drilling just increases the airflow. The increased 
surface area resulting from the holes is probably not important (though 
that is just a guess).

Slotted rotors are a puzzle. The additional surface area for cooling must 
be insignificant. The slots do not penetrate the rotor so airflow isn't the 
advantage. That leaves the cleaning action of the slots as the only 
practical advantage. i cannot believe that street brakes vaporize in any 
significant way, judging from the dust on my wheels at any rate so the 
outgassing idea has got to be largely an illusion.

No question the slots look cool, but for street brakes you're far better 
off using a wheel that covers most of the visible area of the disc, to 
minimize water contamination during wet weather which really can spoil your 
braking at inopportune times. Hey, maybe that's what the slots do. if you 
insist on having open alloy wheels that expose your wheels to contamination 
by dirt and water, the slots are a big advantage. I prefer more sensible 
street wheels myself.
Michael Smith
Calgary, Alberta,Canada
91 Alfa 164L

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