Hydraulic force question

That'd be true if the single piston caliper were not free to center itself. But it can, and as a result applies the same pressure to the pads on both sides of the disc.

Ned Simmons

Every single piston brake I've seen had pads on both sides of the rotor. The pressure that is produced by the single piston is applied to both pade. It's just like a vice, each jaw pushes the same amount, even though only one moves. If you have two pistons, they push against each other with the rotor in between. The force remains the same as long as the area of the piston is the same, but instead of pushing against the other half of the caliper with the other fixed pad mounted on it, the pad is being pushed by the piston.

John

You forgot to put a :-) behind your nonsense^Wstatement.

Or do you really not know the difference between inner and outer forces?

Nick

ACK

NAK

To put an end to this funny discussion (I have put oil into the fire): With one piston, you have a reacting force on the other side of the bracket of exactly the same force coming from the piston (actio = reactio; or summ of vectorial addition of forces must be zero). Now if you introduce a piston on the other side, that piston can only have the same force as the first piston (same pressure, same diameter) and thus just will compensate the actio. One piston actio, the other reactio.

Vector addition! Force has direction!

Think of having a C-clamp with two opposed spindles. Close one spindle with all the force you can bear with your hands. Now close the other spindle with all the force. Will there be a difference? Will you be able to turn the other spindle? No.

So it makes no difference regarding the forces wether there is one piston or two opposed pistons (same diameter).

Nick

You are not doubling the area because the force is colinear and shares a common ground. Because of this the force cannot exceed that generated by one piston. If it did it would drive the other piston back into its bore, but it cant because it is in equalibrium.

Jesus there's a lot of s**te on this thread.

1/ imagine a motorcycle front wheel and brake, it makes things easier.

2/ in the old days iy would be cable and shoes, now it's hydraulic and pads

3/ hydraulics give a mechanical advantage, the smaller "operating" cylinder vs the larger "operated" cylinder, but the flipside is you get less travel on the larger diameter cylinder

4/ if the "operating" cylinder displaces 1 cc of fluid, this doesn't necessarily mean there is any pressure of note in the system

5/ After you take up the slack on "off" or "released" brakes, then, apart from compressibility of the pad and friction material, generally speaking each extra amount of fluid displaced by the "operating" cylinder will inclrease pressure (yes, fluids are supposed to be incompressible, but brake lines expand etc etc

REALLY IMPORTANT from some of the shit mentioned above.

psi or any other pressure measurement is NOT a force measurement and is nothing like a force measure ment

single piston hydraulic press type system versus opposing (identical) pistin brake caliber type system, with the same pistons, piston area and pressures YOU DO NOT get double the force, you do not even get the force evenly applied to both sides cos it already is, what you do get, and all that you get is a floating caliper. this means you get a disk that is being gripped instead of deflected, this means a hard cast disk can be MUCH thinner = much lower unsprung weight

to the OP, the television person was talking complete bollocks

I think if you were to read the responses carefully you'd find only a few glaring errors in reasoning. Most everyone reached the same conclusion, though some in roundabout and not always clearly expressed ways.

Perhaps you'd prefer a thread on WMDs or the circumstances of Vince Foster's death .

Ned Simmons

When they make "Floating" calipers with the pistons on one side, they use one piston with 10 square inches area, or two pistons with 5 square inches of effective working area each. The clamping effect goes through the caliper body, and the caliper moves laterally on the slide pins or rails to apply clamping pressure to the pads on both sides of the rotor.

When they make a four piston fixed caliper, they put four pistons with 2.5 square inch working area each, two on each side. They have the same effective area (10 square inches total), so the clamping forces applied to the brake pads are exactly the same.

The big advantage to a fixed caliper design is that the caliper doesn't have to move laterally to apply and release, it can be bolted down firmly. There are no large caliper slides (that have to transmit braking forces) to get rusty and stick, and cause dragging shoes and other brake problems.

But the four-piston designs cost more to make initially, so when car makers try to save a buck they don't get used. And the Big Three in Detroit wonder why they're going bankrupt...

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you're prolly right, I tend to skim rather than read in depth

dunno who vince foster is, as far as wmd's go I have never had any illusions, if fact the only people who seem to be disconnected from reality are those that rely on the mainstream media H^H^H^H propoganda for their "facts"

the next 20 years sure are going to be interesting times.

Oh, just some guy the Clintons had killed. Unless you believe that he moved his own body after being dead long enough for post-mortem lividity to set in, I suppose.

...or people with selective memory, like the current crop of democrats who pretend that they didn't agree about the WMDs before the war.

Mr. Bergman hit it exactly right. In order to maintain the same clamping force, you must maintain the same square inches of piston area.

A couple of other comments. The goal is to provide maximum moving friction without locking up the rotor. In order to do that, it is important to keep things "consistent." Even loads across the brake bad, lack of flexing in the caliper, lack of cocking, angling, digging, or otherwise flexing of the caliper and its loads in relation to the disk are important.

When all done, race cars take advantage of every little bit they can. Braking is very important. Race cars spend a lot of money and weight to keep their calipers and pads true to the rotors.

Flexing is a bad thing, and floating calipers by definition must move about to do their jobs. Single piston calipers are not as good as fixed calipers.

LOl. What you're saying then, is that 1 x one ton jack will lift as much as 2 x 1 ton jacks? Interesting hydraulic philosophy, I wonder what Bramah would say.

Why is it then, that comparable capacity single piston brake calipers have a far greater piston diameter than the equivalent

2 piston calipers? Brake calipers work on one simple formula:

total piston area x working pressure ÷ pad area = pad pressure psi.

Tom

No. Energy of a moving object is 1/2 mass times velocity squared. Total energy disspiated in a two car crash is the sum of the energy of each car. A 2 ton car slamming into a wall at 50 miles per hour dissipates 1/4 of the energy of a car going 100 into a wall. Two cars that compact the same way driving into each other is really like two cars slamming into a wall. If you consider the rate of deceleration the only measure of a crash, the original statement is sort of true, but still misleading.

I didn't say this. If the jacks work in parallel, they lift 2 tons. But if you stack two jacks, will they lift 2 tons?

hint: The answer is "no"

Nick

What do you mean by "in tandem"? Parallel or serial?

Ignorance is often a subjective attribute. :-)

Nick

Yes, in the case of lifting a car two stacked one-ton jacks would be limited to one ton. When you start pumping the jack on the top and reach the one ton pressure limit, even if you jimmy the relief on the upper jack the relief valve on the bottom jack would open to avoid overloading.

But NOT when you're talking about a brake caliper, that's not the right way to look at it - The object of the pressure would be BETWEEN the two stacked jacks, and it WILL see two tons of pressure - one ton from each side. They are in parallel, but the forces are opposing.

RIGID SURFACE | Jack | Pad

-------- Rotor - Measure Force Here

-------- Pad | Jack | RIGID SURFACE

Know what I mean, Vern?

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