JP Roberts

When I mentioned hitting a pool I was not thinking of rust but rather of
disc warp because of a sudden change in temperature, a known phenomenon in
some Ford Focus.

Yours,

JP

"C.R. Krieger" <warp2_shadow@yahoo.com> escribió en el mensaje
news:a8a578a8.0310151247.6f8cc19e@posting.google.c om...
> "JP Roberts" <1234@yahoo.com> wrote in message
news:<bmjb33$q9a$1@news.ya.com>...
> > Thanks to all for your answers. Of course, I do understand the possible
> > problem of rust formation and extreme temperature changes, for example
when
> > hitting a pool of water after spirited driving.
>
> Apparently, you don't, really. The rust I mentioned comes from
> letting the car sit parked outside overnight where condensation (dew)
> forms on the rotors, forms drips on the inside and outside edges,
> rusts in those areas, and is insufficiently cleared the following day
> because the driver's normal braking pattern is too tentative or
> gentle. The rust then slowly starts cutting away the surface of the
> pad (it's harder than the pad) and the pad gets progressively worse at
> clearing the rust which obviously continues cutting away more pad.
> Quite a nasty syndrome that's easily addressed by braking more
> aggressively to be sure to knock off all the rust daily. Driving
> through water has almost nothing to do with it. The greatest problems
> with rust on rotors come from the car *sitting*, not being driven.
>
> > However, excepting those and extreme circuit driving, I would still
think
> > pad wear must be faithfully proportional to disc wear - after all if
pads
> > wear, then so do rotors at a given rate.
>
> For an individual driver, that's correct, but some drivers can still
> extend their pads' lives by 'smart braking', so your mileage *still*
> may vary.
>
> > Now, if we set stock pads and discs
> > as a reference, then it should be possible to do such calculations as 2
or 3
> > sets. Before I got all your opinions I would have ventured 3 sets but
now I
> > realize I was being too optimistic, maybe.
>
> Fair enough. Two sets isn't a bad rule of thumb.
>
> > Nobody mentioned the thinner the
> > discs - and no I'm not into having them lathe-turned, the worse their
heat
> > dissipation capability becomes, which reduces efficiency greatly.
>
> Good thinking.
>
> > Of course, now the discussion could turn to aftermarket pads and how
> > efficient they are vs stock, then a difference in the number of sets
would
> > sound quite logical to me.
>
> Like PBR Deluxe pads ...
> --
> C.R. Krieger
> "Ignore 'em, m'dear; they're beneath our dignity." - W.C. Fields

Hairy One Kenobi

"Pronto Breakneck" <no_address@example.com> wrote in message
news:nniqovg22vhqu07j7t6qi0doguhevu4ihh@4ax.com...
> On Wed, 15 Oct 2003 08:37:09 +0100, "Hairy One Kenobi"
> <abuse@[127.0.0.1]> wrote:

<snip answer of self>

> >Well, again, comes down to if you're doing the work yourself.. OTOH, in
> >hindsight, I probably should have guessed this - after all, what company
is
> >going to take liability for a set of turned discs, these days?
>
> Rotors should be resurfaced or replaced every time you replace the
> pads.
>
> (I know some people are going to disagree with me about that. Please,
> don't bother - you'll only be talking to hear yourself talk.)

We'll just leave it as "you're misguided", then ;o)

> >Incidentally - have you really never experienced any judder after doing
> >this?
>
> Nope.
>
> There's a factory specification for the minimum thickness of the
> rotors. If the rotors exceed that specification after resurfacing,
> there's no reason to replace them.

Thickness has nothing to do with judder. See snipped text for the reason..
and an example.

An "average" machine shop is, I submit, unlikely to meet the required
tolerance. My guess is that you must be going somewhere that can - as I
said, just a small variation on either side of any disc will cause judder.

--

Hairy One Kenobi

Disclaimer: the opinions expressed in this opinion do not necessarily
reflect the opinions of the highly-opinionated person expressing the opinion
in the first place. So there!

Chris Mauritz

JP Roberts wrote:
> However, excepting those and extreme circuit driving, I would still think
> pad wear must be faithfully proportional to disc wear - after all if pads
> wear, then so do rotors at a given rate. Now, if we set stock pads and discs
> as a reference, then it should be possible to do such calculations as 2 or 3
> sets. Before I got all your opinions I would have ventured 3 sets but now I
> realize I was being too optimistic, maybe. Nobody mentioned the thinner the
> discs - and no I'm not into having them lathe-turned, the worse their heat
> dissipation capability becomes, which reduces efficiency greatly. So my
> original question was something like, will 3 sets make the rotors so thin
> that there will be a noticeable reduction in efficiency?
>
> Of course, now the discussion could turn to aftermarket pads and how
> efficient they are vs stock, then a difference in the number of sets would
> sound quite logical to me.

Before I start, let me just say that I usually replace the rotors each
time I replace the pads. It's easier, gives me peace of mind, they look
pretty, etc....

As far as cutting a rotor on a lathe is concerned, it really doesn't
impact the overall ability of the part to dissipate heat by a meaningful
amount as long as it is still within spec. Consider that a normal
"turning" results in only a few thousandths of an inch of material being
removed from each side of the rotor. Visit your local machine shop and
see how much powdered metal is shaved off a rotor being cut. I suspect
that if you weighed the rotor before and after the difference would be
insignificant. So you're really not changing the ability of the rotor
to act as a heat sink if you're not taking away a meaningful amount of
mass and other factors remain constant.

But like I said, I always just put new ones on my car. It's easier.

Cheers,

C