On Fri, 31 Jul 2020 11:50:43 -0700, The Real Bev wrote:

> That would be me. The rotors looked like a beginning lathe project --
> proof that they're made of softer stuff than the pad's backing plate
> nubs. I could feel and hear the grinding, but the braking was just as
> good as before it started. When I had to brake carefully to avoid
> hogging in I figured I needed to deal with the problem. At the time the
> rotors (Pep Boys, used) cost only $10 each. The cost wasn't the
> problem, just the time.

Hi The Real Bev,

I've worn _plenty_ of pads down to the rotors, where the grooving limit on
rotors is huge when you can find the spec. The limit that most people check
is the thickness, which, depending on factors, is usually two sets of pads
in my experience (but I sometimes get three sets of pads out of a rotor).

It's interesting that the cold/hot friction rating for steel on steel is
very similar to E/E pads, which I find a lot of people buy who don't know
anything about brake pads but what the MARKETING people tout (e.g.,
"ceramic" on the package could mean no more than a few spec of clay dust,
based on my personal talks with the Axxis marketing team).

Basically, the only valid data you have is what's printed, by law, on all
US pads sold for passenger vehicles, which is the cold/hot friction rating.
<http://faculty.ccbcmd.edu/~smacadof/DOTPadCodes.htm>

Anything else, IMHO, is marketing bull****.

> I wouldn't let it go that long now. I love my little Corolla and don't
> want to hurt it. Rear drums, but I've never noticed a problem with
> insufficient brake power from the rear. OTOH, how would I know?

Drums are different, and more of a pita, IMHO, than disc brakes.
o The drums have an inspection port, but I always found it rather useless.

While you "can" hurt a caliper by metal on metal heating up things, going
to the point of a millimeter or two of that is safe, as far as I know.

In my situation of mountainous driving causing inboard wear on the front
tires, I rotate the wheels every few months anyway, so for disc brakes, I
inspect them at every rotation.

That's where the calculation of miles remaining can be of use.
o Given current data, something around 4K miles per millimeter seems ok.

That means I'll tell her she has likely at least 20K miles to go.
--
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