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Which Sierra Calipers
MakeEverything - 30/3/10 at 08:54 AM

Hi All,

Ive got normal sierra calipers on solid discs on the kit car, and the mechanical handbrake ones on the rear.

I want to upgrade to four or six pots for more braking efficiency, but i dont know which ones will fit straight on.

Anyone done this before? I dont want to keep buying bits that dont fit, then have to sell them on!

cd.thomson - 30/3/10 at 08:57 AM

No doubt it will ignite a debate but I am under the impression that the £200+ 4 pot calipers (like the kits from rally design) are all about weight reduction rather than significantly higher braking efficiency.

What about changing to the larger cosworth front discs and mintex pads as a more affordable option?

ETA - of course, fit 4-pots if you like! I plan on doing that as an early winter upgrade once its on the road but mainly for bling factor

[Edited on 30/3/10 by cd.thomson]

ChrisW - 30/3/10 at 09:10 AM

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.

With some decent pads that should be plenty for a Seven-type car. If you need better pedal feel, why not think about a servo?

Chris

iank - 30/3/10 at 09:14 AM

If you have braking problems with those discs putting on 4-pots is unlikely to improve braking. (Unless your car is going faster or is significantly heavier than a sierra).

If you are having problems then it's probably because the master cylinder is the wrong bore, pedal pivot isn't in the right place, racing pads that aren't up to temperature, or you simply aren't used to the feel of servo'ed brakes.

Can you lock up the brakes if you push hard enough?

MakeEverything - 30/3/10 at 09:18 AM

For Brakes, im not too worried about the weight (within Reason), but want them more for their efficiency etc.

Larger discs will only prevent overheating, which will require larger wheels.

My kit car isnt a seven type car, so behaves differently. I already have a servo, and as said, its not hte feel, but the efficiency that im after.

MakeEverything - 30/3/10 at 09:19 AM

quote:
Originally posted by iank
If you have braking problems with those discs putting on 4-pots is unlikely to improve braking. (Unless your car is going faster or is significantly heavier than a sierra).

If you are having problems then it's probably because the master cylinder is the wrong bore, pedal pivot isn't in the right place, racing pads that aren't up to temperature, or you simply aren't used to the feel of servo'ed brakes.

Can you lock up the brakes if you push hard enough?


Im not having problems, i just want better braking efficiency because im going from 130hp to over 230.

iank - 30/3/10 at 09:32 AM

quote:
Originally posted by MakeEverything
quote:
Originally posted by iank
If you have braking problems with those discs putting on 4-pots is unlikely to improve braking. (Unless your car is going faster or is significantly heavier than a sierra).

If you are having problems then it's probably because the master cylinder is the wrong bore, pedal pivot isn't in the right place, racing pads that aren't up to temperature, or you simply aren't used to the feel of servo'ed brakes.

Can you lock up the brakes if you push hard enough?


Im not having problems, i just want better braking efficiency because im going from 130hp to over 230.


But will you be going any faster? If not it makes no difference*. i.e. road car. On the track you might need better brakes as your speed will be higher, but the callipers won't help the efficiency much - bigger diameter discs will (you get a mechanical advantage with the pads pressing at a greater radius). As you say thicker discs just reduce the tendency to fade.

* Brakes convert kinetic energy to heat in order to stop you. Your kinetic energy is 0.5*mass*velocity^2.

[Edited on 30/3/10 by iank]

MakeEverything - 30/3/10 at 09:44 AM

quote:
Originally posted by iank
But will you be going any faster?


Errrr.... a bit....

iank - 30/3/10 at 10:30 AM

quote:
Originally posted by MakeEverything
quote:
Originally posted by iank
But will you be going any faster?


Errrr.... a bit....


So it's on the track you are looking at? On the road your acceleration will be better, but it's only speed that makes the difference to the brakes. It's a common misconception that big bhp requires expensive brakes.

My point is purely that bhp means nothing to the brakes except indirectly. If you don't break the law (or only break it sanely) then on the road it will make no difference if you are already happy with their current performance.

In either case calipers won't make the difference you're looking for, it's really only pad material and brake diameter count.

Brommers - 30/3/10 at 11:45 AM

Assuming the brakes aren't getting too hot to work properly (in which case you need vented discs or better brake cooling) there are three things which affect the efficience of a braking system:

1. Disc diameter
2. Pad compound
3. Whether the pad is operating in its optimum temperature range

Changing the calipers will have next to no effect on overall braking efficiency. If you can tell the difference in braking efficiency from just changing the calipers, and you're not a top-level professional racing driver, then you're in the wrong job...

MakeEverything - 30/3/10 at 01:07 PM

quote:
Originally posted by iank
quote:
Originally posted by MakeEverything
quote:
Originally posted by iank
But will you be going any faster?


Errrr.... a bit....


So it's on the track you are looking at? On the road your acceleration will be better, but it's only speed that makes the difference to the brakes. It's a common misconception that big bhp requires expensive brakes.

My point is purely that bhp means nothing to the brakes except indirectly. If you don't break the law (or only break it sanely) then on the road it will make no difference if you are already happy with their current performance.


No, im not looking for track performance.

The existing calipers need overhauling, so i see that as an opportunity to upgrade.
Yes, they (once overhauled) are probably enough to stop the car, but by upgrading to four pot, or even six pot, then there is a greater surface area of the pad touching the disc, giving greater efficiency with less effort.

I didnt really post for a debate on what it is people think i want. I KNOW what im after, i was just wondering what other people had done to achieve it.

cd.thomson - 30/3/10 at 01:13 PM

quote:
Originally posted by MakeEverything
I KNOW what im after, i was just wondering what other people had done to achieve it.


Other people with lightweight sierra based kit cars achieve better braking efficiency by fitting larger discs and different compound brake pads.

I'm not sure what more it is you're after.

If you specifically want 4-pots for the weight reduction and bling factor than rallydesign do a sierra kit at an affordable price. Be aware that people do experience quite a lot of brake squeal with them.

MakeEverything - 30/3/10 at 01:20 PM

OK, Thanks. Ive heard that the six pots from Rally Design are squeaky, and that the handbrake mechanism isnt too clever, so was thinking about itenms fitted to existing road cars.

The bling factor does come into play, but primarily, if im going to overhaul calipers then id rather overhaul a better set than i have currently.

The accelleration speed will be improving, so i want the Decelleration speed to improve with it. Of course, its all relative to traction.

turbodisplay - 30/3/10 at 02:53 PM

The bore size of the caliper will affect force applied, larger bore more force on pad for givenline pressure.

Darren

MakeEverything - 30/3/10 at 03:13 PM

quote:
Originally posted by turbodisplay
The bore size of the caliper will affect force applied, larger bore more force on pad for givenline pressure.

Darren


Correct, though the more combined surface area of all four pistons equals a greater force on the pads Vs the two cylinders, increasing the efficiency without increasing the bore of the line or the master cylinder.

iank - 30/3/10 at 03:35 PM

quote:
Originally posted by MakeEverything
quote:
Originally posted by turbodisplay
The bore size of the caliper will affect force applied, larger bore more force on pad for givenline pressure.

Darren


Correct, though the more combined surface area of all four pistons equals a greater force on the pads Vs the two cylinders, increasing the efficiency without increasing the bore of the line or the master cylinder.


Sorry it changes the braking effort (if you don't have a servo) but does nothing for the braking efficiency. If you can lock the brakes on your current setup you'll just be able to lock them with less force on the pedal with the new callipers.

Mr G - 30/3/10 at 04:28 PM

Cossies run 280mm

My XR4i front upgrade thread

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.

With some decent pads that should be plenty for a Seven-type car. If you need better pedal feel, why not think about a servo?

Chris

MakeEverything - 30/3/10 at 06:42 PM

quote:
Originally posted by iank
quote:
Originally posted by MakeEverything
quote:
Originally posted by turbodisplay
The bore size of the caliper will affect force applied, larger bore more force on pad for givenline pressure.

Darren


Correct, though the more combined surface area of all four pistons equals a greater force on the pads Vs the two cylinders, increasing the efficiency without increasing the bore of the line or the master cylinder.


Sorry it changes the braking effort (if you don't have a servo) but does nothing for the braking efficiency. If you can lock the brakes on your current setup you'll just be able to lock them with less force on the pedal with the new callipers.


Making the effort exerted, more efficient????????

iank - 30/3/10 at 06:53 PM

quote:
Originally posted by MakeEverything
quote:
Originally posted by iank
quote:
Originally posted by MakeEverything
quote:
Originally posted by turbodisplay
The bore size of the caliper will affect force applied, larger bore more force on pad for givenline pressure.

Darren


Correct, though the more combined surface area of all four pistons equals a greater force on the pads Vs the two cylinders, increasing the efficiency without increasing the bore of the line or the master cylinder.


Sorry it changes the braking effort (if you don't have a servo) but does nothing for the braking efficiency. If you can lock the brakes on your current setup you'll just be able to lock them with less force on the pedal with the new callipers.


Making the effort exerted, more efficient????????


Unless your measure of efficiency is leg effort no. Brake efficiency is a measure of rate of conversion of kinetic energy to heat. Pedal pressure doesn't come into it - that's brake feel.

By all means spend your cash on aluminium 4 pots, they will make the car handle a little better and look very nice. But don't fool yourself that they will dramatically reduce your braking distances.

MakeEverything - 30/3/10 at 06:57 PM

quote:
Originally posted by iank

Unless your measure of efficiency is leg effort no. Brake efficiency is a measure of rate of conversion of kinetic energy to heat. Pedal pressure doesn't come into it - that's brake feel.

By all means spend your cash on aluminium 4 pots, they will make the car handle a little better and look very nice. But don't fool yourself that they will dramatically reduce your braking distances.


Im not. Thats why im looking at something already fitted to a road car.

Brommers - 30/3/10 at 07:20 PM

quote:
Originally posted by MakeEverything

The existing calipers need overhauling, so i see that as an opportunity to upgrade.
Yes, they (once overhauled) are probably enough to stop the car, but by upgrading to four pot, or even six pot, then there is a greater surface area of the pad touching the disc, giving greater efficiency with less effort.


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.

quote:

I didnt really post for a debate on what it is people think i want. I KNOW what im after, i was just wondering what other people had done to achieve it.


Oh, in that case I just went to Rally Design's website and spanked some cash on a set of Powerlite kits all round. Luvverly.

gazza285 - 30/3/10 at 07:31 PM

quote:
Originally posted by MakeEverything
Making the effort exerted, more efficient????????


Making a longer pedal.

MakeEverything - 30/3/10 at 08:21 PM

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.

MakeEverything - 30/3/10 at 08:22 PM

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.

boggle - 30/3/10 at 09:21 PM

parachute?????

cd.thomson - 30/3/10 at 09:22 PM

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

Brommers - 31/3/10 at 12:19 AM

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.

MakeEverything - 31/3/10 at 08:13 PM

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.

Brommers - 31/3/10 at 08:34 PM

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]

Brommers - 31/3/10 at 08:39 PM

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...

scudderfish - 31/3/10 at 08:42 PM

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.

RIE - 1/4/10 at 07:50 AM

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.

mcerd1 - 1/4/10 at 05:52 PM

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]