Show me your wheels...

[nightfire]

wytbishop, you rock.

[Daninski]

wytbishop, I'll keep this short and to the point for I fear incuring your wrath. lol As you know Pressure equals Force over Area. If we have a master cylinder delivering fliud pressure to a system with 4 1" brake pistons vers delivering pressure to 8 1" brake pistons your end result is the 4 pistons are reciving higher pressure between them (per square inch lets say). Your last statement may be in need of correction.

[onlytrueromeo]

Old Danny, you said the corect answer yourself, proving Charlie correct!

P=F/A so, if you have the same P, F has to increase w/ A!

Look at it like this:

Say P = 2, A=2 and F=4 initially.

If you increase the area to 3, and hold pressure constant, to maintain the balance, F must increase to 6.

P*A=F

See?

EDIT* I see you're asking about pressure changing - we're not talking about pressure changing, but the effective force on the piston/caliper/brake. The pressure will only change if you change the master, upgrading the size or number of pistons WILL INCREASE braking force!

[Daninski]

No No NO. How can you say your increasing the area. The damn master cylinder is the same one we started with. We're increasing the area of the brakes by going from a single piston brake to double piston brakes right. So if the master cylinder is producing the same pressure but it's now being divided between 8 pistons vers 4 (double the surface area) how have we gained pressure. I may be wrong but I think your applying the formula backwards, Young whipper snapper. lol

[onlytrueromeo]

LOL

I may be young, but I'm going to engineering school and I know Charlie is an engineer as well. If I'm wrong, god help whatever poor soul I design things for.

We aren't increasing the pressure, or saying that we are. The master cylinder has nothing to do with it. Pressure IS determined by the master and the size of the line. (which is why upgrading to SS lines is good, because they can hold the pressure slightly better than rubber) So pressure is NOT determined by the brakes.

What we are talking about is the Force applied to the brakes. If you change the effective area the fluid is acting upon, you are increasing the effective force. The effective area here is the size/number of pistons. More pistons = more area. More area = more force. NOT PRESSURE. The pressure is being applied TO the area which creates a resultant force.

If you were to increase the pressure, that would also increase the force, but we are holding pressure constant here. If you hold P constant, then the right side of the equation must remain constant too - ie to balance a larger piston area, the force needs to increase - its either that or the pressure decreases.

[wytbishop]

No wrath Dan...just physics. I'm a happy engineer.

The master cylinder creates the pressure. The wheel cylinders experience that pressure.

so the pressure in the system is given by P = F/A1, where A1 is the area of the cross section of the master cylinder. Then the resulting pressure P acts on the wheel cylinders and the force applied at the brake pad is given by F = P*A2, where A2 is the area of the cross section of the brake caliper cylinder(s).

The pressure can only change if the master cylinder gets bigger. So knowing that the pressure in the system is only dependent on the size of the master cylinder and how hard you press the pedal, we can consider it constant.

If you look at the equation, P =F/A...which rearranges to F = P*A we see that if P is constant and A increases, F must increase.

therefore, if the size of the pistons in the caliper is increased, or the number of pistons increases creating a net increase in area, the braking force must increase as well.

[Daninski]

Ok the effect of area is not something I'd debate as in some cases area is good in others bad like wider tires in wet weather. Less lbs per sq in on the road surface so more skiding. Also there's coefficient, at some point more tire surface becomes less important. bla bla Anyway, I'll run the numbers again (taken from Riddick). SS lines are simply better because they don't inflate like rubber does. I'll admit I'm still confused over how adding piston area at the brakes can do anything but reduce surface pressure but like you said that's where area come into play. One way or the other, old or not this dog is never going to stop learning or questioning,,, whipper snapper. My 5c

[wytbishop]

I feel I need to add...

It could be argued that because the pistons in the calipers travel when applied that the volume of the system is increasing and that with added pistons the volume increases more but given that the pistons only travel a mm or so the change in volume is a very small percentage of the total volume of the system.

[onlytrueromeo]

More volume will aid in heat distribution = less brake fade. Im not talking about the change in volume as the brakes are depressed, but overall change in volume from 1 system to the next.

[wytbishop]

More volume will aid in heat distribution = less brake fade. Im not talking about the change in volume as the brakes are depressed, but overall change in volume from 1 system to the next.

I was referring to the increased loss of pressure due to additional pistons in the caliper, but as I think about it, there is really no issue because your foot would just push that little bit further to maintain the pressure.

I want to do a diagram.

[onlytrueromeo]

Yeah, its a similar reason as to why you told me that changing the master wasn't necessary when upgrading to a disk swap - you just push a little harder to stop...am I right in my thinking?

[Daninski]

Sing to the tune of "I lost on Jeapardy"

I was there to match my intelllect, oh on MX3. Against wytbishop, and onlytrueromeo, both with a PHD. I was tense, I was nervous, I guess it wasn't my nite , they both gave the answers but I couldn't get the questions right, -ight, -ight.
I lost on MX3, Baby, oooh oooh ooh ooh.
I lost on MX3, Baby, oooh oooh ooh ooh.

[onlytrueromeo]

I don't got no PHD lol.

Can't win em all - and heck, half the stuff I say I'm pulling out my arse w/ what I think makes sense and am trying to justify it w/ equations.

[Daninski]

Ya I know, I was just trying to be funny. Kind of a spin off on the engineering thing. So bottom line bigger brakes or not? Sounds like if we could just fit larger sufaced pads on our cars we'd be ahead of the game or pads with better grip. Bigger brakes do look cool I have to admit.

[wytbishop]

But I made a diagram...