62 replies to this topic

[JohnTurbo]

Basically no sadly. The exige system...maybe.

Edited by JohnTurbo, 01 August 2013 - 09:28 PM.

[GeorgeBC]

Same front calipers as mine Chris. Till hot i found the same pads front and rear fine. Hot i tried various pads and they defo lock rear first. At oulton i found pf01 front and the sh*t mintex rear good but was still worried about stamping on the pedal still need to try pagids with rs14 front and the blue not so good ones on the rear. Got them just need to try them. SteveA was on standard calipers and he had borrowed my pf01 for the fronts with the rc6 on the rear i think it was the bump that did it and i hope it was as i felt bad afterwards.

[JimmyJamJerusalem]

As Fez said before though with different compounds you run the risk of the bias changing as different compounds fade and bite at different rates....

[GeorgeBC]

Thats true. If it wasnt for steves accident i think i would of done the same thing

[speedster]

Same front calipers as mine Chris. Till hot i found the same pads front and rear fine. Hot i tried various pads and they defo lock rear first. At oulton i found pf01 front and the sh*t mintex rear good but was still worried about stamping on the pedal still need to try pagids with rs14 front and the blue not so good ones on the rear. Got them just need to try them. SteveA was on standard calipers and he had borrowed my pf01 for the fronts with the rc6 on the rear i think it was the bump that did it and i hope it was as i felt bad afterwards.

Placement of the 2 pots the same as Chris?

[GeorgeBC]

Yep

[JohnTurbo]

Typically compounds from the same manufacturer follow similar temperature profiles - so look at the graphs ideally when mixing pads. That is a recognised route...hawk even state a particular pad is used mostly for that purpose.

[JimmyJamJerusalem]

I can't remember the compound names but piagids worked well.

[Winstar]

* 44.5mm front pistons (stock) and 36mm rear pistons (stock) give a 60:40 ratio of braking from front to rear.

Interesting you consider stock to be optimum I though general the thinking (and in my experience) is that the rear is under braked and fitting a higher friction pad rear is beneficial.

As for coefficient curves then the Pagid RS42, RS14 and RS15 all follow the same trends

 

 

 

Edited by Winstar, 01 August 2013 - 10:46 PM.

[JohnTurbo]

I had thought the same..it even struck me that this could be partly why Chris is ok....but then there is a line of thought that you want more front bias on a track car due to the extra grip, you can load the front axle more. In reallity my wheels lock at nearly the same time under haaaard braking, and I outbrake everything on trackdays usually. This was not so when I the past I had front or rear dominance. Im not an expert. ..and some opinion comes into everything. In the end I fitted not tbe ultimate brakes to my car, but a system that stops hard all day on £50 pads and disks...because that was actually what I wanted.

[Winstar]

Right..AP 7600s front and the 2pots rear (with same pads all round) is too rear biased. I've tried it, and George and Darron have tried it. Its not good. - Expect to die.

 

 

A few points:- (Some recycled from PM conversations past)

 

* Number of pistons is totally irrelevant to braking effort

 

* Overall piston area ON ONE SIDE of the disk gives braking effort. (FYI 1 pot designs (such as the stock brembos) exert the same force as same-size 2 pots because they are on slides and so there is a reaction force from the fingers equal to the force from the 1 piston.)

 

*The VX hydraulic pressure in the line is the same at the rear as the front.

 

So:-

 

* 44.5mm front pistons (stock) and 36mm rear pistons (stock) give a 60:40 ratio of braking from front to rear.

* If you use the "bolt on" ap calipers with asymetric pistons then you should be on 31.75mm/36mm leading/trailing
   This is 10% more braking than standard - if you've gone for 308mm disks that's 16% more braking than standard.
   Balance = approx 64:36 front/rear.

   This is why it upsets bias. Actually this will *feel* fine, but you'll kill front pads and disks and you won't be stopping as quick as someone with     stock brakes!!

 

* If you run FTR brackets thats a 44.5mm piston on rear, giving balance:- 56:44 (With the 4 pot fronts - without it would be WORSE!)

For this setup you'd ideally run pads with 10% - 15% more bite on front (than the rears), you also may find the pedal slightly more spongy and this could warrant a bigger diameter master (ie the 1.1" subaru one).

 

 

Solutions:-

 

Jimmy went for the brake bias adjuster, and I gather it works great.

I also spoke with George about his setup and he has found the above has worked great with good pads front and 1144s rear. (Ap 4 pot front, and FTR brackets)

 

I used my FTR with Hispecs and the balance was 60:40 due to the big Hispec pistons.

A note on pedal feel - assuming correct bleeding, a nice hard pedal is mostly a function of a low slave/master ratio, high caliper stiffness, high line stiffness (ie hard pipes are best, then braided flexi). The aps should at least be pretty stiff.

The killer with any other setups than stock brembos left in place is the handbrake for a road car - also its worth considering weight you are adding to the unsprung mass which is not great for handling. Because my MGTF calipers have smaller pistons than the off the shelf AP cp7600s, I'm back to JUST the stock rears and the balance is 60:40. Perfect.

The suggestion that has been traditional on the forum is to use stock discs as better ones don't offer anything more - which is pretty dumb, the stock cooling channels are very thin, though for me using stockish disks can contribute to a capable system which will have a lower running cost in terms of consumables.

Oh and Steffen's setup will be about the best around - with the older type ap fronts (38mm pistons), FTRs and a light spot caliper for handbrake.
- Ideally with the larger master cylinder and lightweight alloy belled discs. 60:40 balance, light and stiff.

 

 

 

John do these calcs take into account the ratio of disk to tyre? using the numbers from slingboard's thread it can vary the bias a few % each way.

[siztenboots]

The suggestion that has been traditional on the forum is to use stock discs as better ones don't offer anything more - which is pretty dumb, the stock cooling channels are very thin, though for me using stockish disks can contribute to a capable system which will have a lower running cost in terms of consumables.

if there is a better option without going belled rotors, that give wider airgap then please share

there must be lots of other caliper options if you make up brackets


Boxster: 40 mm + 36 mm > 1257 mm² + 1018 mm² = 2275 mm²

whats needed is a spreadsheet , something on the lines of this

[JohnTurbo]

There are a lot more factors than just that...even things like suspension softness, rotating inertia, the effect of engine braking.... You also might want different bias depending on conditions. I was trying to keep it relatively simple.

[fezzasus]

Side note: anyone retaining the Brembo rears for the handbrake should keep fluid in the calipers to stop them from seizing.

[JohnTurbo]

Also relating to porsche calipers. ..they weigh a tonne, need machining heavily and adaptors to fit and either machining the hub or running massive (heavy) v6 saab 330mm disks. I bought some and chose to sell them.

[fezzasus]

 

The suggestion that has been traditional on the forum is to use stock discs as better ones don't offer anything more - which is pretty dumb, the stock cooling channels are very thin, though for me using stockish disks can contribute to a capable system which will have a lower running cost in terms of consumables.

 

 

 

Okay, this is moving off topic so I apologise, but here goes.

 

I've been looking into other belled rotor options. The AP options on the EP and ES websites are expensive for what they are, and the VX220 community tend to be fairly blinkered when it comes to considering other options.

 

The key to remember here is that these are standard Vauxhall brake discs, and there are lots of options out there. HiSpec is one that comes to mind.

 

HiSpec universal bells: http://www.hispecbra...rsal Bells.html (10 mm offset required). Can be drilled for various PCDs. £46 ea. for standard 288 mm disc duplication

 

HiSpec 288 mm/26 mm rotor: http://www.hispecbra...uk/page482.html £56.06 ea.

 

Therefore price for a pair of HiSpec rotors suitable for the VX; ~£200

 

Want to go bigger?

 

300 mm bell- £47.50

300 / 28 mm (need to confirm if calipers can take this thickness - anyone?) - £56.06

 

Therefore still ~£200

[siztenboots]

also to consider is how much work you expect the brakes to do, it would be easy to massively over spec

 

consider that some of us are now running double the amount of torque , corner approach speeds are much higher , you could lighten the car , you could add grip so you can have a high corner entry speed

 

kinetic energy is equal to 0.5 multiplied by the mass multiplied by the square of the speed

 

so if you have higher approach speeds , and after braking , lower entry speeds , and different car weights

 

quick spreadsheet to show how much KE , or work the brakes have to do

 

 

 

 

[Acidpopstar]

Im not an expert. ..and some opinion comes into everything. In the end I fitted not tbe ultimate brakes to my car, but a system that stops hard all day on £50 pads and disks...because that was actually what I wanted.

Sorry if I've missed this but what exactly is your brake set up please?

[JimmyJamJerusalem]

 

Im not an expert. ..and some opinion comes into everything. In the end I fitted not tbe ultimate brakes to my car, but a system that stops hard all day on £50 pads and disks...because that was actually what I wanted.

Sorry if I've missed this but what exactly is your brake set up please?

 

 

lol, don't go there!!  It's not a three line answer

[fezzasus]

 

Im not an expert. ..and some opinion comes into everything. In the end I fitted not tbe ultimate brakes to my car, but a system that stops hard all day on £50 pads and disks...because that was actually what I wanted.

Sorry if I've missed this but what exactly is your brake set up please?

 

 

https://www.google.c....50165853,d.ZG4