| [ Total Views: 1377 | Total Replies: 20 | Thread Id: 22181 ] |
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 Cam
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| posted on April 26th, 2004 at 11:56 PM |
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hrrm... twin calipers.
What do you guys think of this set-up?
I would of thought that the gain in reciprocating weight and less disk surface exposed to the air would outwiegh the gain in brake force
.
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Oasis
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| posted on April 27th, 2004 at 12:37 AM |
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Interesting. No idea, but maybe 2 calipers = less fricton therefore less heat, so disc surface wouldn't be a problem. They look small and light so
weight may not be significantly different either.
"Tell him 'We've already got one'"
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Cam
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| posted on April 27th, 2004 at 09:23 PM |
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I assume the weight would be more evenly balanced on the spindle. But the friction comes from the pads themselves doesn't it? If so I can't see
there being any more or less from having two calipers.
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oval TOFU
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| posted on April 27th, 2004 at 09:48 PM |
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It would just come down to brake pad surface to rotor suface area wouldn't it? I think the rotor would be more inclined to heat up faster since there
would be double(?) the 'normal' friction area: hence the cross drilling and slots and separate hat and rotor setup...? Cam racer-boy, do my
ramblings sound semi-correct?
...and Robert's ya father's brother...
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Anthiron
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| posted on April 27th, 2004 at 09:54 PM |
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yes but by having the twin calipers it would reduce the amount of time that the calipers and disc are in contact therefore i would be led to beleive
that the heat generated would be about the same
62/60 model bug eye baja bug, (Full Build in Progress)
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oval TOFU
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| posted on April 27th, 2004 at 10:08 PM |
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I think again, it just comes down to surface area in contact wouldn't it and PSI? So one caliper exerts pressure X to stop the car in Y meters,
having two calipers would require X/2 pressure for each caliper thus still totalling X pressure to stop the car in distance Y...
yeh?
Which leads me to ask, if I had 185/60/13's front wheels, would they heat up the brakes less or more when compared to, say, 165/75/15 (ie: a much
taller wheel)...?
the small wheel would require less torque from the brake pads, but would make more revelotions, where as the 15" rim would require more torque and
have fewer revelutions of the wheel....
??
...and Robert's ya father's brother...
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oval TOFU
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| posted on April 27th, 2004 at 10:10 PM |
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i'm only a designer not a engineer... so tell me to FO if I'm talking crap!
...and Robert's ya father's brother...
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Anthiron
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| posted on April 27th, 2004 at 10:16 PM |
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well i am neither of those things so u are ahead of me im just applying my brain in a generic sense......u are talking about the twin calipers being
used to stop the car in the same distance or amount of time or whatever as a single caliper...........i would be led to beleive that with 2 calipers
both if applied could brake with the same force as a single caliper and therefore stop the car quicker than a single caliper and exposing the pads to
friction for a shorter amount of time but at the same pressure therefore creating an even amount of friction heat because of the shorter time of
contact.....which would be the same as a single caliper because it would have to be in contact with the disc for longer............am i totally off
course here?
62/60 model bug eye baja bug, (Full Build in Progress)
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Cam
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| posted on April 27th, 2004 at 10:22 PM |
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I think you guys about both right. What I'm wondering is if the two smaller calipers are better or worse than a single HUGE caliper.
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oval TOFU
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| posted on April 27th, 2004 at 10:26 PM |
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well.. lots of pro car racers cant be wrong?
...and Robert's ya father's brother...
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oval TOFU
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| posted on April 27th, 2004 at 10:28 PM |
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i dont think balance of weight on that axis would really matter would it?- Since the axel isn't a fulcrum for anything? I think one caliper has less
shit to go wrong with it.. less hoses, easier to bleed? etc?
[Edited on 27-4-2004 by oval TOFU]
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modulus
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| posted on April 27th, 2004 at 10:41 PM |
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There is a simpler way to look at this; try seeing the problem from an energy perspective. Brakes (including but not limited to disk brakes) convert a
car's kinetic energy into heat (and a bit of brake squeal). The work to be done depends on the starting speed before braking, end speed after braking
and the car's mass. (The rate of doing work depends on how hard you stand on the pedal and available grip of the tyres).
Most disk brakes are capable of (or very close to being capable of) locking up a front wheel at most speeds (or could do so with a bit more pressure
applied), so twin calipers won't stop you quicker; a single caliper setup is enough.
So, with twin calipers, the energy dissipated is the same for a given stopping situation; also we can see that the heat that needs to be dissipated by
the rotor is the same. What changes is that the work done (and the rate of doing work) is approximately halved for each caliper; thus the friction
surfaces do less work (each) and the heat generated at each caliper is less for a given braking task.
When motorbikes are fitted with twin front disks, something similar applies, but the rotors only have to dissipate half the heat each.
So, the work to be done (and therefore the heat to be dissipated) doesn't change with twin calipers, nor with larger or smaller wheels, nor with
larger diameter rotors. The way in which the work is converted into heat may, however, be altered by the brake configuration. Twin calipers might add
to unsprung mass, but with twins you might be able to use a lighter rotor, reducing both unsprung and rotating mass.
In theory, bicycle brakes work in exactly the same manner, but in practice mine always bind when I want to go and slip when I want to stop, so there
is a physics distortion field at work there.
hth
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2443TT
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| posted on April 27th, 2004 at 10:45 PM |
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Isn't that a honda civic with Z type brakes. I've seen these same calipers installed as singles on honda integra's and civics (in the hot 4's
mag). They are supposed to be the among the best you can get (for honda's). Imagine the plumbing required for it though...
I reckon porsche got it right by using 4 or 6 pistons of diferent sizes from one end of the directional caliper to the other. Simple and and
effective.
Cheers,
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Cam
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| posted on April 27th, 2004 at 10:50 PM |
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Nah, it's a Nissan 350Z. I just saw the pic and it got me curious.
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pete wood
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| posted on May 6th, 2004 at 09:22 PM |
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cooling
Modulus was spot on. Heat is where it's at.
I'm sure there are many ways to remove the heat.
Air cooling (on finned calipers) is quite effective if you can duct enough to the components.
(It's not bad for engines either I hear )
Someone once told me F1 cars have water cooled calipers to get the heat away from the rotor.
They also use a twin caliper setup.
Accordingly twin, finned, light-weight calipers on a ventilated, cross-drilled disc would probably work a treat.
As long as the ducting to them was well done.
Getting the duct plumbing exactly right would be a bit interesting though. :o
Look wicked on a German look car though:thumb
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Che Castro
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| posted on May 7th, 2004 at 12:10 AM |
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looks like a Nissan 350Z??? or maybe a Honda S2000.
Jon
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Che Castro
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| posted on May 7th, 2004 at 12:13 AM |
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I agree with modulus
My stocker 4 drums can lock up the wheels easy, but they cant dissapate heat for shit. Also part of the reason they lock up is because drums are
self-energising - its hard to modulate them when they are about to lock up but thats another story
Another reason why discs are so much better
Jon
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oval TOFU
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| posted on May 7th, 2004 at 12:40 AM |
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whatchoo talkin bout Willis? I mean Castro? self-energising? Care to write about it here or u2u me? I'm interested with what you mean..
cheers
Chris
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BiX
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| posted on May 7th, 2004 at 08:51 AM |
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I think he means one of the two shows is actually being dragged onto the drum while the other is being pushed therefore when at close to lock uo, you
have to release a lot of pressure to get the shoe from being dragged onto the drum?
I have no sympathy for my car, only the wallet that pays for it!
Go hard or go home!!!!
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modulus
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| posted on May 7th, 2004 at 12:20 PM |
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Pretty much what Bix said. In the diagram below the shoes are hinged at a common point on top; the left shoe is "leading", the right one is
trailing; it's easy to see how the leading one will force itself onto the drum, whereas the trailing one tends to be pushed away from the drum by its
rotation.
Leading shoes are *much* more effective than trailing shoes; most drum braked cars have twin leading shoes on each front drum (2 pivots) and 1
leading/1 trailing on the rear drum. The reason for the trailing shoe on the rear drum is to give some effective braking when in reverse.
hth
[Edited on 7-5-2004 by modulus]
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Che Castro
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| posted on May 13th, 2004 at 10:44 AM |
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A good analogy is dragging a stick in the dirt, if you drag with one end trailing behind you it moves easily, however if you try to push it forward
with one end ahead it forces itself into the dirt. The brake shoe basically pushed between the drum and the cylinder like a wedge by the rotation of
the drum.
The Beetle drum brake shoes are fully floating ones, which means that they are not fixed to any hard point - they have no pivot like the pic above,
they are held in position by the springs and the spring clip things, so both the leading and trailing shoes energise. This makes it hard to control
the brake because as you push the pedal the braking effort is amplified by this action and it makes it difficult to feel when the wheels are about to
lock up - where you get the most effective braking action.
I guess the only good thing i like about drums is that the handbrake is stronger than disc handbrakes (any that i've tried)
[Edited on 13-5-2004 by Che Castro]
Jon
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| posted on May 13th, 2004 at 06:58 PM |
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Not abad idea V8 supercars dont use them abig 6spotter ,4spotter are as good the only idea for using twin set up would stop brake fade maybe! JVL
| Quote: | Originally
posted by Cam
What do you guys think of this set-up?
I would of thought that the gain in reciprocating weight and less disk surface exposed to the air would outwiegh the gain in brake force
.
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KruizinKombi
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| posted on May 14th, 2004 at 11:12 AM |
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I think that one of the benefits of twin calipers is (assuming total surface area & pressure is the same) that each caliper, having 1/2 the total
surface area, would only create half as much heat before that section of the rotor is again exposed to cooling air. Yes, the rotor only gets half the
cooling time before passing the next caliper and heating up again, but never reaches the same momentary maximum temperature as with a single caliper
of twice the pad area.
Also (I guess), having a caliper on each side of the spindle would help to balance the bearing pressure in the hub.
It may also be possible that two smaller calipers would be even lighter than one single, and the calipers themselves would dissipate heat faster than
one single (Higher caliper surface area/Pad surface area ratio).
I'm no engineer either, but these are the only possible benifits I can think of... :alien
Kruizin Kol
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