Date:         Wed, 6 Nov 2002 14:40:18 -0000
Reply-To:     Clive Smith <clive.harman-smith@NTLWORLD.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Clive Smith <clive.harman-smith@NTLWORLD.COM>
Subject:      Re: Drilled brake discs
Content-Type: text/plain; charset="iso-8859-1"

> I am no expert, but I thought the whole point of cross drilling was to
dissipate heat.

Dissipate heat maybe yes, DISTRIBUTE IT EVENLY - No.
the result - non-uniform stress distribution whose strains mitigate towards
cracking, hairline or worse.

Short term transient heat dissipation is achieved simply by mass, greater
thickness for a given diameter > thermal inertia.
Its the longer term heat dissipation that drilling should improve, through
induced airflow (and a turbulent boundary layer).
So you lose on transient thermal inertia and maybe gain on prolonged braking
anti-fade, with the downside that should the temperature gradients become
excessive, a drilled disk is more likely to warp and/or crack. Possibly,
more clever hole profiles and certainly attention to the finer points of
drilling, reaming and radiusing/deburring would mitigate this possibility to
a greater or lesser degree.

Re: Conductivity - Hard steel is much worse than cast iron and low carbon
steels, stainless is quite an insulator c.f. carbon steels.
Carbon-carbon composites  (you call them graphite, well Courtaulds invented
it so its still carbon composites to us) as originally developed here for
Concordes brakes and subsequently F1 cars are of course the ultimate
material - if we are able to keep the whole thing at the right temperature -
F1 cars do of course and Concordes brakes heat up pretty quickly I should
think - it was this weight saving that virtually made a full payload
possible to Washington from London - NMPKT!

Clive
'88 Syncro Transporter


----- Original Message -----
From: "80 Westy Pokey" <pokey@VANAGON.ORG>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Wednesday, November 06, 2002 11:40 AM
Subject: Re: Drilled Rotors vs. Big Brake Kit


> I am no expert, but I thought the whole point of cross
> drilling was to dissipate heat.
>
> Thanks,
> Chris
>
>
> ---- Original message ----
> >Date: Tue, 5 Nov 2002 19:11:36 -0800
> >From: Doktor Tim <doktortim@ROCKISLAND.COM>
> >Subject: Re: Drilled Rotors vs. Big Brake Kit
> >To: vanagon@GERRY.VANAGON.COM
> >
> >The only good thing drilled rotors will do is shed water
> for better braking
> >in the rain. Every hole is less mass to absorb heat, more
> potential for
> >stress risers and cracks, and cooler running is just
> speculation. If you
> >need more powerful brakes, put on the bigger calipers and
> rotors. I don't
> >think an 0.1 liter boost in motor size is going to justify
> the need of any
> >brake expense beyond stock. Verify those wheels/tires weigh
> no more than
> >stock or you can start pulling the suspension mounts apart.
> >
> >At 06:16 PM 11/05/2002, you wrote:
> >
> >>I've got a Syncro w/ 15" 205/65's. Also getting a 2.2L
> Euro Cars motor
> >>installed, so a bit more H.P.
> >>I know the big brakes are obviously better, but more $
> then the drilled
> >>rotors from Fast Forward.
> >>Will I still get a decent increase in performance w/ the
> rotors or should
> >>I go w/ the big brakes?
> >>Trying to save $ if I can.
> >>Thanks