From: R1004@vmcms.csuohio.edu
Subject: Re: disc brake question
Organization: CSU
Date: Fri, 11 Sep 1992 17:12:50 GMT

In article <1992Sep11.143346.4773@julian.uwo.ca>
wlsmith@valve.heart.rri.uwo.ca (Wayne Smith) writes:
 
>All I ever see is this kind of arm-waving!
>No-one has shown that heat dissapation affects the braking action,
>but sure, high heat can either dammage/deform parts and/or boil the
>fluid (both of which I really really doubt happens in drum systems
>for the average driver).
>(Don't send me e-mail, like I've already gotten, that you drive on
>race tracks and get your brakes hotter than spit and all the rest..)
 
The brakes are a HEAT SINK, if they can dissapate heat faster
they will work better.  If the brake works better there is more
stopping power.
 
 
>
>Has it ever occurred to anyone that you have more friction surface on
>shoes than on disks?
>
Since disks are more efficient the surface area need not be
as large.
 
>Because they don't want to put hold-back springs on them.
>(A case where "if it works without them, we won't put them in")
>
 
Can't be much drag to worry about, If I put the wheel up
in the air it'll spin.  I don't think that calls for
hold back springs.
 
>
>Because they have to add a second set of rear drums for the safety brake,
>or add a complicated mechanism to the rear disks for the saftey/parking
>brake.
 
That's why the car companies stay w/ rear drums, saves $.
 
 
>
>All I'm doing here is asking for more than arm-waving about heat
>dissapation as to why disks are better than drums...
>
Because the brake system has a finite capacity to transfer heat.  If
the hardware cannot dissapate the heat as fast as it come in the
components will heat and eventually overheat.  As the components
heat up they loose effectivness.  If you can throw away heat faster
the better off you are.
 
    Could some of this be why some of the PPG pace cars use
    water COOLED brakes?  Hmmmm...
 
>
>True (about the drum).  But I still can't figure why (it seems) so many
>people need their rotors turned...
>
'cause they believe Sears or Midas when they say, "Gee, you really
need your rotors turned"
 
>>1. The rears don't do that much of the work,
>That's how they design them.  Why?  I don't know.  No car engineers
> (apparently) want to tell us what's going on.
 
When you begin to stop a car there is a weight transfer from the
rear to the front.  With the additional weight on the wheels it
takes more work to slow them (the wheels).  It's not a communist plot.
 
>
>>and 2.  They are CHEAPER!  (drum brakes)
>Again more arm-waving (how can they be cheaper? They've got more parts.)
>
>you've forgotten about the mechanical saftey/parking brake setup too.
No, I haven't.  That's why drums are cheaper, because there is no
need to add:
 
>... a second set of rear drums for the safety brake,
>or add a complicated mechanism to the rear disks for the saftey/parking
>brake.
 
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Bob Martel               |
bob2@cua3.csuohio.edu    |  Lady luck must have been a wonderful girl
R1004@vmcms.csuohio.edu  |    -She's never been a friend of mine!
                         |                        Alan Parsons Project
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