misconceptions on drilled rotors and SS lines etc

[jonathan coates <alfa@domain.elided>]

In message , Richard Welty <rwelty@domain.elided> writes
>At 11:13 AM 3/17/99 -0500, JJK1204@domain.elided wrote:
>>>Are you sure? I was always told that it was not for cooling, but to allow
>the
>>hot gas, which forms on heavy braking, to escape from between the pad and
>>rotor. 
>
>correct. cross drilled rotors, however, are only one of several approaches to
>this issue, and there are others that work better:
>
>slotted rotors
>    the slots, cut across the face, tangentially to the inner radius of the
>swept
>    area, also relieve the pressure, with substantially less risk of weakening
>    a vented rotor. there is a picture of a set of slotted rotors on a
>Penske car
>    on one of Carroll Smith's book covers, as i recall.
>
>slotted pads
>    this is why you will find brake pads with a vertical slot in the face
>of the
>    friction material.
>
>the downsides of cross drilled rotors, some of which have already been
>mentioned:
>
>1) risk of weakening vented rotors due to holes drilled at inappropriate spots
>
>2) reduction of size of rotor, reducing its utility as a heat sink
While I do NOT profess to know enough to comment on this subject, I
would like to put questions to those who know (you know who you are,
well some think they know, others dont know they know).
The idea of drilling holes through the disc to release the "fumes" from
the pad as it vapourises due to being heated mercilessly is a tempting
thought, however if the pad is giving off these gases, isn't the
opposite pad doing the same, in the other direction, down the same hole?

Does the drilling increase turbulence of the air round the disc, and
thus cooling?

Do the brake people promote drilled discs to "cheese grater" the pads
away so people buy more?

Others (not God) have mentioned that the drilling affects the pad
contact area, well the braking force is not dependent upon pad area as
the braking force is the clamping force times the friction coefficient.
If the area is reduced, then the force per unit area is increased to
compensate.
Just wondered
Oh and no, I wouldnt want to buy enhanced heat sink effect discs made
from 1 inch plate so dont go trying to sell me them.
- -- 
jonathan coates

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