From: welty@cabot.balltown.cma.COM (richard welty)
Subject: Re: Threshold braking (was Re: "tank" superchargers)
Organization: New York State Institute for Sebastian Cabot Studies
Date: Thu, 1 Oct 1992 23:10:28 GMT

In article <1992Sep27.220752.15101@lonex.rl.af.mil> koziarzw@lonex.rl.af.mil (Walter Koziarz) writes:
>>i know somebody is going to jump on me for saying that there is no
>>difference, but consider -- brakes convert forward motion into heat;
>>on a given trip, the only sure way to reduce wear and tear on the brakes
>>is to convert less motion into heat -- either by discarding all the random
>>taps on the brakes that so many drivers seem to love, or by driving
>>slower.  braking earlier and lighter doesn't change _anything_ except
>>the distance over which you are converting forward motion into heat;
>>if you are pressing the braking system to its limit (usually only happens
>>at race tracks), this could be meaningful, but on the street, no, it isn't.

>Richard, I'm truly appalled!  While you are correct in asserting that the
>quantity of *HEAT* converted will be the same, the same heat be converted
>in less time will create a greater temperature.  Since it has been noted
>that temperature is the enemy of friction-materials, how can you possibly
>assert that 'wear and tear' will be unchanged?

i held my tongue for several days so that i wouldn't post something
that i'd be ashamed of later.

it is posited right at the start of this thread that we're talking
about street applications where the driver is not currently very
agressive, and the driver wants to do some learning.  given that
this is the case, i maintain that a beginning driver is unable to
use their brakes effectively enough to do serious damage with one
or three tries at threshold braking on the way to and from work
every day.  i can do serious damage to my brakes at watkins glen or
summit point in a very short period of time, but in these cases we're
talking about 2:50 laps of the glen and 1:50 laps of summit with little
time for brake cooling between brake applications; the context is entirely
different.

your comment is only applicable once we start talking about braking
by the serious, in a serious context.  in the context of this discussion,
it constitutes a cheap bit of sniping from the sidelines, rather than
a useful contribution to the discussion.

>Is this more material from references that defy reality (i.e. disk brakes
>will *always* outperform drums -- counter-example *any* tractor trailer)?

and this is what REALLY ticked me off; dragging in an irrelevant comment
from another, apparently dead discussion thread.  not only that, but you
have completely ignored two aspects of that discussion:  first of all,
that discussion was in the context of `why are all cars using disk brakes
now', and secondly, that a person much more knowledgable about brakes
on tractor trailers than either of us commented that disk brakes for
large trucks are in fact under development due to the inadequacies of
drums in that application.

futher study of Puhn's _Brake Handbook_ reveals that in very large
disk brake systems, there are problems with caliper flex and movement
that can only be solved at considerable cost; this reinforces comments
suggesting that perhaps drum brakes are common on tractor trailers
because they're a shitload cheaper.

i didn't reply to the previous thread because i thought others
had adequately discussed the subject; you should NEVER assume that
my silence constitutes admission of defeat -- sometimes it just means
that i think enough bandwidth has been wasted.

richard
-- 
richard welty                            518-393-7228
welty@cabot.balltown.cma.com
  ``if you can read this, mario, you're too close''
    -- bumper sticker seen on a CART safety truck