Didn't actually get to DRIVE one (probably because I couldn't fit my fat
ass into its bucket with a shoehorn and a gallon of vaseline), but I
worked with a CASCAR team for a season... they all had front and rear
discs, and lemme tell ya, on the short oval, those brakes would spend
half the circuit glowing red... but they cooled down pretty quick out of
the apex. Of course, having dedicated ducting to scoop air from the air
dam and pipe it right onto the rotors helped :)
Except that I happen to be right.
I see so many people go on and on about the friction area of drums vs that
of discs, and cite the better heat-shedding capabilites of discs. The
problem is...all that is IRRELEVANT.
Rear brakes of either type generate so little heat that fade is NOT even
close to being any kind of a concern. Heat-fade is a concern with the
FRONTS (which handle 80% of braking effort), which is why all road cars use
discs at the front these days.
Rear discs heat up so little in use they cannot even reliably burn off the
moisture they collect, which is why they rust up so badly. Rear drums don't
heat up much at all either, but they are basically sealed from the weather.
A test if you want to try it. Procure the use of a rear disc-braked car and
a rear drum-braked one. Drive both vehicles up to 30 mph or so on a
deserted road. Now apply the parking brake hard, just short of lockup, as
though you were going to stop the car using just that brake.
You will find both systems feel exactly the same, and any "fade" will be
identical on both.
Of course, I assume both cars have rear brakes in good repair...
That's my experience, too. Here in Arizona rust isn't a problem, but discs
still have more noise problems than drums do and the slide pins are still
troublesome. The only problem I've ever had with rear drums is worn-out
self-adjusters. Replace the self-adjuster assembly (usually when the linings
are worn out) and they are good for the rest of the life of the car.
I'm convinced front drums are what gave drum brakes their reputation as
second rate. I learned to drive on cars that had drums all around, and they
were completely unacceptable for highway use.
a number of manufacturers don't have slide pins on rear disks - they use
old fashioned twin-piston calipers because there are no steering
geometry constraints. [single piston front calipers were originally
born of the desire to create negative steering scrub radius.] bmw,
volvo and subaru use twin-piston iirc.
i'd say it differently - it's front drums that /prove/ they're second
rate! their action is non-linear and they can only dump heat /through/
the drum metal by conduction, not direct to atmosphere like a disk.
They are definitely second rate for the front, where they have lots of heat
to dump. Drum brakes fade like crazy in that application. That isn't an
issue in the rear.
From Edmunds techcenter @ http://tinyurl.com/6r6kh : ".. the truth is that
today's disc/drum setups are completely adequate for the majority of new
cars. Remember that both disc and drum brake design has been vastly improved
in the last 20 years. In fact, the current rear drum brake systems on
today's cars would provide better stopping performance then [sic] the front
disc setups of the '70s. And today's front disc brakes are truly exceptional
in terms of stopping power. Combined with the fact that between 60 and 90
percent of a vehicle's stopping power comes from the front wheels, it's
clear that a well-designed, modern drum brake is all that's required for
most rear wheel brake duty."
You'll note that drums are still used almost universally in semi-trailer
rigs, where massive stopping power is of utmost importance.
Of course, if you really want to confuse the issue, you can always look
at the "hub brakes" used on train cars....
it's true that most trailers use them, but it's not because of superior
is the way of the future. and hopefully, rigs having to use runaway
ramps will be a thing of the past.
eh? that's bullshit. whoever wrote that is basing it on the erroneous
supposition that because drum brakes are still used, there must be a
reason, and is just guessing that it's about performance. but it's just
a guess and has no basis in fact if they'd bothered to look up
performance figures. the reason drum brakes are used is cost and hand
brake implementation. and market segmentation creeps in there too to
what's required and what's best are not the same thing.
not that simple.
regarding the single/double thing, there's a few factors at play, one
being that the caliper casting for single piston needs better q.c. to
take the fatigue load of spanning the disk in a single piece and the
more complex shape. with twin piston, there are two halves that bolt
together and q.c. on a single more compact part is easier to cast. the
extra piston is more expensive, but the housing can be cheaper and
machining access is easier.
but the biggest factor is steering geometry. by far. that's why you
have "double piston" calipers like this:
to get negative scrub radius, you have to get the hub face as close to
the bottom swivel as possible. you can do that easily with single
piston [single sided] caliper, but not easily with double [sided] unless
you have shallow pistons and thin pads. that's not acceptable for
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