2008 SP STi brakes

John, caliper pistons are just a small fraction of a greater system, that system starts with:
Curb weight
Tire diameter
CG Height
Wheel base
Weight distribution
Pedal ratio
Master cylinders size
Caliper piston size
Effective radius
Pad coefficient of friction
Pad friction characteristics

Things you can change to affect braking effort, torque and feel are: the pedal ratio, caliper pistons, m/c's, disc diameters, and pad mu.

Now you tell me that calipers HAVE to have a certain piston size when one can manipulate several other aspects of the system. C'mon John, piston sizes are "fairly common" mostly due to packaging not specific requirements. Now you're giving sizes 1.5 and 1.625 are 38mm and 41. Now these were used initially in the Gr4 cars, on 13 INCH WHEELS ese, in cars that weighed less than 1000 kilos, now you tell me that a 1300kg impreza on 15 inch wheels (tire torque is very important in sizing brakes) cant use a 41mm/44mm because it will be too touchy? Its only 15% difference in piston area from a 1.5"/1.625" to a NASCAR 41/44. THATS the difference in master cylinder steps. A 3/4 master to the next size up 13/16 is 16%. Dont you think its a wash off?

C'mon we dont have to do everything monkey see monkey do, theres many ways to skin a cat amigo.

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Cosworth
John, caliper pistons are just a small fraction of a greater system, that system starts with:
Curb weight
Tire diameter
CG Height
Wheel base
Weight distribution
Pedal ratio
Master cylinders size
Caliper piston size
Effective radius
Pad coefficient of friction
Pad friction characteristics

Things you can change to affect braking effort, torque and feel are: the pedal ratio, caliper pistons, m/c's, disc diameters, and pad mu.

Now you tell me that calipers HAVE to have a certain piston size when one can manipulate several other aspects of the system. C'mon John, piston sizes are "fairly common" mostly due to packaging not specific requirements. Now you're giving sizes 1.5 and 1.625 are 38mm and 41. Now these were used initially in the Gr4 cars, on 13 INCH WHEELS ese, in cars that weighed less than 1000 kilos, now you tell me that a 1300kg impreza on 15 inch wheels (tire torque is very important in sizing brakes) cant use a 41mm/44mm because it will be too touchy? Its only 15% difference in piston area from a 1.5"/1.625" to a NASCAR 41/44. THATS the difference in master cylinder steps. A 3/4 master to the next size up 13/16 is 16%. Dont you think its a wash off?

C'mon we dont have to do everything monkey see monkey do, theres many ways to skin a cat amigo.

Very aware there ways to skin a cat---and I also read better

---I said Gp4 Escort 4 x 1.50" want the AP part number...? (this is for the others Paulinho)


http://www.apracing.com/product_details/race_car/brake_calipers/historic_range/cp2361-closed_backed_caliper-38.1mm_bores-%C3%B8267x21mm_disc.aspx

And they were initially used in F3 cars---


Then I said:

Quote

Later GrA cars 1150-1250kg
Fronts either 2x 1.5" + 2 x1.625"
or occasionally on very fast events 4x 1.625"

And I've not NOW I'm giving sizes blah blah, I have been looking at and measuring and checking sizes since 1985 on cars....and telling people what I see.
And been very very serious about brakes beginning winter 75-76.....

And yes of course you can say "Curb weight
Tire diameter
CG Height
Wheel base
Weight distribution
Pedal ratio
Master cylinders size
Caliper piston size
Effective radius
Pad coefficient of friction
Pad friction characteristics

Things you can change to affect braking effort, torque and feel are: the pedal ratio, caliper pistons, m/c's, disc diameters, and pad mu.

And i say dio! it is a miracle! [angelic choir ON] all thsoe different cars with different wheelbase, different weight and weight distribution , almost all with 15" wheels, so many things different- and virtually all use the same 38/41 caliper....and dozens of privateers too..

You can call it "monkey see- monkey" do but you too often forget who we're answering questions for and what budget is....most important that the average reader does not intend to get job being a brake engineer or designer, just as they are not going to become an engine builder or designer when all they need if They just want things to work..

And in any case we all learn by watching... It is quicker and far higher chance to get thing "right"

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

*tirekicker post*

Available sizes of stuff and all... if you start with a blank slate, you can make the brake torque work right. Same brake torque per pedal effort, all sorts of ways to skin a cat.

In practical terms, and I've been looking for a while, all the used NASCAR stuff tends to be equivalent of 1.75x4 or 1.75x2 and 1.872x2 front, and 1-1.25ish rear. That's ignoring size factors of the calipers too. Off the shelf front rally calipers seem to be 1.5-1.625 or something I think the Subaru 4-ports are 40mm, which is a bit over 1.5ish. Total area is pretty similar to a 2x1.5 2x1.625 caliper, so swapping over shouldn't fuck with the brake bias or torque per pedal effort. And from what I'm seeing, the AP homologated VO Group N brakes for the front of the STI are the CP6720 - 2x1.625, 2x1.375 pistons, so relatively similar to John's rule of thumb, 'bout identical in area to 4x1.5" actually.

Now, going even more practical, if there were bigger master cylinders that bolted in place of stock, or you went to dual masters with a balance bar, you could do whatever you want because you could size the hydraulics to make it work. But there's not a hell of a lot of master cylinder options for the Subaru without going to dual masters and a balance bar, are there? And it seems like it'd be easier to not have to reinvent the wheel.

I dunno. Some day when I have infinite bucks I'm going to build a caliper stiffness test rig - I really do wanna see how bad things like the Wilwood FNSL6R actually are compared to higher buck stuff. The AP 8350s are a lot more attractive at most of our budget level than the 6720s, I'd wager.

I can see that I'm rattling your cage because you're starting to say the same thing as I am but in different words just for sake of a pow wow. Here's what I mean:

Quote
john vanlandingham
And i say dio! it is a miracle! [angelic choir ON] all thsoe different cars with different wheelbase, different weight and weight distribution , almost all with 15" wheels, so many things different- and virtually all use the same 38/41 caliper....and dozens of privateers too..

So if all those different cars with different braking requirements can use similar piston sizes, means that bigger or smaller pistons dont really make much of a difference in the end result. Like I said above, the piston sizes are just one of the features of the design inputs. 6 one way half dozen the other Like I said above, piston sizes are fairly standard due to packaging. And as I said earlier on, the NASCAR calipers are too wide anyhow.

And I also try to give budget conscious advice, I just wont recommend cheap shit for the sake of being cheap. I actually tend to advise people NOT to go for pedal boxes and to keep stock calipers, to just run a good disc and pad.



Edited 2 time(s). Last edit at 05/11/2014 07:33PM by Cosworth.

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mekilljoydammit
Now, going even more practical, if there were bigger master cylinders that bolted in place of stock, or you went to dual masters with a balance bar, you could do whatever you want because you could size the hydraulics to make it work. But there's not a hell of a lot of master cylinder options for the Subaru without going to dual masters and a balance bar, are there? And it seems like it'd be easier to not have to reinvent the wheel.

HUH??? What're talking about cuz? Whats the purpose? Why in the HELL would you want a bigger master on an STI??? I have the GrN setup and the freaken pedal is as hard as superman's head! Thats because the caliper pistons are TOO small, and the master TOO big. In the end yes a balance bar with dual masters would be the solution. But I still fail to see what you were trying to talk about in your post.

Quote

I dunno. Some day when I have infinite bucks I'm going to build a caliper stiffness test rig - I really do wanna see how bad things like the Wilwood FNSL6R actually are compared to higher buck stuff. The AP 8350s are a lot more attractive at most of our budget level than the 6720s, I'd wager.

Ummm you dont have to have infinite bucks, just really know what're you doing when you go in the garage. A little mechanical inclination is all thats needed. Caliper stiffness test right = Dial indicator. Put it on the piston wall and measure how much it moves. (when the brakes are hot of course)

Doing this on a phone, so live with me not doing fancy quoting.

First bit, was trying to say that if you have a desired brake torque per pedal force, you might not be able to stay close to it with something using NASCAR surplus caliper style piston area. I'm not, and am unlikely ever to, running an STI with a real group N setup, so I've got no idea why they set up the hydraulics ratio the way they did, but I was assuming that something close to the factory setups made sense and so was something to emulate.

As for making the test rig, that's no problem. Problem is, I don't have the cash to buy, even at eBay prices, every caliper I want to know about to test.

Quote
mekilljoydammit
Doing this on a phone, so live with me not doing fancy quoting.

First bit, was trying to say that if you have a desired brake torque per pedal force, you might not be able to stay close to it with something using NASCAR surplus caliper style piston area. I'm not, and am unlikely ever to, running an STI with a real group N setup, so I've got no idea why they set up the hydraulics ratio the way they did, but I was assuming that something close to the factory setups made sense and so was something to emulate.

As for making the test rig, that's no problem. Problem is, I don't have the cash to buy, even at eBay prices, every caliper I want to know about to test.

Ah ok the phone thing. That why I dont like to do it. As for the brakes... well you dont need to be explaining me the concepts, I have a small notion of how that whole enchilada works.

As for using a NASCAR piston area, it would actually be preferable for an STI (vs GrN) because you could actually get enough force to lock up the tires and not have blisters on your feet at the end of a rally.

Yeah, just explaining my thinking - in the absence of personal experience, assume that the homologated stuff makes sense.

So why *is* the group N setup sized like that, then? I gotta assume that there were other caliper options that'd fit with more piston area.

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mekilljoydammit
So why *is* the group N setup sized like that, then? I gotta assume that there were other caliper options that'd fit with more piston area.

Beats me... maybe some retard at Prodrive specced it like that because he maybe used the advertised coefficient of friction of pads? And the reason why they kept it like that over the years is even more bizarre, maybe the same reason why Murica likes to reelect shit presidents?

But on the other hand the Evo has a good ratio with their GrN Brembo setup, much better braking!

Would a Performance Friction ZR34 caliper be a good choice, for the front of this car?

Quote
sidewaez
Would a Performance Friction ZR34 caliper be a good choice, for the front of this car?

details? piston sizes? pad length, thickness?
link?

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Blake--

There's a bunch of sizes for that caliper….

http://www.pfcbrakes.com.au/caliper_details.php?ID=34.323

Got something in mind?

These seem to be roundy-round specific with their leading/trailing left/right talk, but maybe they're something?

Beats me.

---

Andrew Steere
Lyndeborough, NH
KB1PJY

Quote
fiasco
Blake--

There's a bunch of sizes for that caliper….

http://www.pfcbrakes.com.au/caliper_details.php?ID=34.323

Got something in mind?

These seem to be roundy-round specific with their leading/trailing left/right talk, but maybe they're something?

Beats me.

That link takes you to much faster info than the US website, which is slow but has the other half of the info.

34.323.410.440.11 and 34.323.410.440.12

Max rotor dia : 323mm
pistons: 41 and 44mm

pad size: 130 x 40 mm 19mm thick kinda spendy though

the roundy round guys seem to use them with the 11.75" x 1.25" rotor blanks

I wouldn't say I had it in mind I'm just trying to find a caliper that'll work, since almost everyone poo poo'd on the Wilwood stuff and AP is just way too expensive

as far as I can tell the master cylinder is 15/16" and I doubt we'll switch to a pedal box.

I do like the idea of removing the ABS pump and "leaving the controller" care to elaborate?

http://www.performancefriction.com/forums-blogs/blog/2014/01/Renault-Sport-Technologies-selects-PFC-Brakes-for-Clio-RS-R3T-Rally-Car

Food for thought. Weirdish pad shape; in the PF compounds anyway, doesn't really seem to be more expensive than Superlite shaped ones on cursory poking around, but not sure if there's the whole range of compounds for them. I'd expect there to be but dunno! https://www.pegasusautoracing.com/productselection.asp?Product=PF7934 for the pad shape. Other places have other compounds too.

Interesting option maybe.

Note that I think the AP 8350s are about the same price as the ZR34s, new for new.

Man you're better at the internet than me, that R3 clio is still way lighter than our SP STi but I bet it's heavier than an R2 Siesta, New ZR34's seemed to be around $500 ea retail,

I'm still curious about what piston sizes would better compliment our 15/16" master cylinder...