cd.thomson
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| posted on 30/3/10 at 09:22 PM |
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quote:
Originally posted by MakeEverything
quote:
Originally posted by gazza285
quote:
Originally posted by MakeEverything
Making the effort exerted, more efficient????????
Making a longer pedal.
Not gonna happen. Car is finished in that sense, and the pedal is as long as it can be with the space i have.
He means that the pedal will move a greater distance thats all 
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Brommers
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| posted on 31/3/10 at 12:19 AM |
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quote:
Originally posted by MakeEverything
quote:
Originally posted by Brommers
Actually, pad area has nothing to do with braking efficiency. As confirmed by the Wilwood's technical pages. Force = area times
pressure'n'all - a larger pad means a lower pressure per area on the disc for an equivalent amount of force.
Exactly my point.
Erm, your point being that a larger pad will make no difference to the relationship between the force you exert on the pedal and the force exerted on
the brake disc by the pads, and therefore, in fact, making no difference to the braking efficiency?
If you're dead set on having multiple pot alloy calipers, as seems to be the case, then knock yourself out - it's only money after all.
But don't think it'll affect your braking performance, because it won't.
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MakeEverything
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| posted on 31/3/10 at 08:13 PM |
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quote:
Originally posted by Brommers
quote:
Originally posted by MakeEverything
quote:
Originally posted by Brommers
Actually, pad area has nothing to do with braking efficiency. As confirmed by the Wilwood's technical pages. Force = area times
pressure'n'all - a larger pad means a lower pressure per area on the disc for an equivalent amount of force.
Exactly my point.
Erm, your point being that a larger pad will make no difference to the relationship between the force you exert on the pedal and the force exerted on
the brake disc by the pads, and therefore, in fact, making no difference to the braking efficiency?
If you're dead set on having multiple pot alloy calipers, as seems to be the case, then knock yourself out - it's only money after all.
But don't think it'll affect your braking performance, because it won't.
Its not hte size of the pad im necessarily looking to increase, rather the pressure applied to the back of it.
As an example;
(disregarding the servo etc at this point, because it will be present in both cases.)
A degree of effort (F) is applied to the pedal which in turn pressurises the caliper and extends the cylinder (C1).
F=C1 - which is what i currently have with a single pot caliper.
If i replace the single pot with the twin pot, then i get;
F=(C1+C2)
Twice the amount of force delivered, for the same amount of effort - which is what i mean by more efficient braking.
Im not hell bent on spending money, nor increasing the number of braking pistons per side, but i dont see anything above that is evidence enough to
make me think that doing so WONT make any difference. I asked a simple question, thats all.
Mr G's linked historical post above answers the question very well and is physical proof of what it is i want to achieve.
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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Brommers
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| posted on 31/3/10 at 08:34 PM |
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quote:
Originally posted by MakeEverything
Its not hte size of the pad im necessarily looking to increase, rather the pressure applied to the back of it.
As an example;
(disregarding the servo etc at this point, because it will be present in both cases.)
A degree of effort (F) is applied to the pedal which in turn pressurises the caliper and extends the cylinder (C1).
F=C1 - which is what i currently have with a single pot caliper.
If i replace the single pot with the twin pot, then i get;
F=(C1+C2)
Twice the amount of force delivered, for the same amount of effort - which is what i mean by more efficient braking.
Im not hell bent on spending money, nor increasing the number of braking pistons per side, but i dont see anything above that is evidence enough to
make me think that doing so WONT make any difference. I asked a simple question, thats all.
Mr G's linked historical post above answers the question very well and is physical proof of what it is i want to achieve.
The position with regard to single pot calipers is a bit complicated, since the slider section screws up what would otherwise be a simple equation.
In fact, the way the slider section works means that if you go from a single pot sliding caliper with an piston area C to a twin-pot caliper with two
pistons each with an area C there wouldn't be any difference.
Leaving that point aside, it's true that if you go from one 2, 4 or 6 pot caliper with a piston area C to another multi-pot caliper with a
piston area 2*C then you'll get double the force exerted by the pads for the same force exerted at the pedal end. However, you'll also
have twice the travel at the pedal. Less effort = longer travel - you don't get something for nothing. Effectively the hydraulic system is
working like a lever - you can make it easier to lift up a load by making a lever longer, but it means you'll have to move the end of the lever
further.
Increasing the effective area of the piston calipers has the same effect as reducing the diameter of the MC, and hence the area of the piston in the
MC. And, indeed, if you want greater 'leverage' in the hydraulics system, switching to a smaller diameter MC (if one's available)
is usually a simpler and cheaper option than changing calipers.
But if, as you say, you don't have any spare pedal travel, then either making the piston area on the calipers larger, or making the piston area
on the MC smaller, means you'll have a more 'efficient' system in that you'll need to press the pedal less hard to get the
same force at the pads, but it also means you're going to run out of pedal travel...
P.S. There's a useful guide to the physics of braking
systems by Stoptec, who know a thing or two about brakes, which tells you everything you need to know...
[Edited on 31/3/10 by Brommers]
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Brommers
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| posted on 31/3/10 at 08:39 PM |
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quote:
Originally posted by MakeEverything
Mr G's linked historical post above answers the question very well and is physical proof of what it is i want to achieve.
Erm, he kept the same calipers and just fitted bigger discs...
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scudderfish
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| posted on 31/3/10 at 08:42 PM |
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Just to throw something else into the mix. 4 pot calipers with the same piston area as 2 pot calipers will exert more braking torque as the effective
distance from the hub that they operate at (at the centre point of the piston) is greater than in the two pot case.
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RIE
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| posted on 1/4/10 at 07:50 AM |
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I'm sure you guys know of this site http://www.carbibles.com/brake_bible.html this article goes into (great!) detail about the physics of brakes
and braking. As already said by a couple of people:
- less physical exertion will be required to depress the pedal at the expense of greater pedal travel to give an equivalent braking force
- braking is about heat dissipation (kinetic energy converted to heat energy - energy cannot be created or destroyed) - discs with better heat
dissipation will improve braking performance.
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mcerd1
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| posted on 1/4/10 at 05:52 PM |
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quote:
Originally posted by ChrisW
The XR4's, 4x4's and Cossies had 260mm front discs instead of 240's on standard Sierras. They're a bolt on upgrade, and
reasonable cheap to do.
the cossie 4x4 (and granada 24v cossie) use even bigger 278mm discs 
the 260mm one were on the XR's, non-cossie 4x4's and any sierra with ABS (granada's have a 5 stud version using the same caliper)
the cossie 2wd's have a 283mm disc with an iron 4 pot caliper - however the cossie upright is different and these arn't a strait swap -
they can be made to fit the std. sierra upright but its total PITA and not worth it as they weigh a ton 
dax do an upgrade kit that keeps the std. 240mm calipers but spaces them so you can use the larger cossie discs (the increased leverage give you the
upgrade)
you'll find the offset on the discs is alot shallower on the 4x4 ones - which may cause a problem - normally all it takes is a coulpe of spacers
and a longer bolt, but that depends on the combination of disc / caliper you pick....
[Edited on 1/4/10 by mcerd1]
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