62 replies to this topic

[fezzasus]

And from what I remembered SteveA sold his rear caliper brackets stating he had not had time to fit them.

 

A word of caution, mixing brake pad types is a really bad idea with the data we have available. They have different initial bite and they have different temperature-friction curves. The combination of this means that as you go around a track the brake bias can move around the car depending on the temperature of the brakes and frictional properties.

[Sticky]

Tbh i am going to repaint them black at some point. Pheonix motorsport made my brackets. Piece of p*ss to fit aswell.

Do they stock the brackets or did they do a one off for you?

[chris_uk]

They do them off the shelf, but they aint cheap. So just to clarify, steve didnt have 2 pot brakes on the back just a harder compound pad on the rear so when the fronts started to fade and loose traction coupled with going over that crest before the corner making the rear end become unweighted / light and subsiquently lock the rears thus sent him spinning?

[techieboy]

I think 70% of that accident was that bump, 20% was no ABS and 10% was down to the difference in compound affecting F/R bias.

[jameso]

I think 70% of that accident was that bump, 20% was no ABS and 10% was down to the difference in compound affecting F/R bias.

Totally agree. It was the unloading of a or the rear wheels over a bump that caused that

[chris_uk]

Thought as much.

[speedster]

Thought as much.

OK chris... So you got the brackets, bolted them on, connected and bled the brakes (using same pad compound all round) and off you go?

[Winstar]

I think 70% of that accident was that bump, 20% was no ABS and 10% was down to the difference in compound affecting F/R bias.

I'd say more than that no ABS, IIRC it's programed to not allow the rear wheels to lock up whether it would have saved the situation at track speed is the question though

[chris_uk]

Thought as much.

OK chris... So you got the brackets, bolted them on, connected and bled the brakes (using same pad compound all round) and off you go?

Wheel off, disc off, hub off, bolt bracket to hub and refit. Attach brake lines, bleed (remembering to turn the calipers) then fit. When i first had then on i used ds2500 pads on the front and mintex1144 pads on the back.

[Sticky]

They do them off the shelf, but they aint cheap.  

 

'Not cheap' being......?

[Firthy]

 

I think 70% of that accident was that bump, 20% was no ABS and 10% was down to the difference in compound affecting F/R bias.

I'd say more than that no ABS, IIRC it's programed to not allow the rear wheels to lock up whether it would have saved the situation at track speed is the question though

 

 

Yep I'd say it was the other way round personally...... the over riding issue was the fact that the RC6's have a ton of bite and that had ruined the F-R balance.

 

Its like driving round trying to slow down using the hand brake unfortunately it was only a matter of time before they locked...

 

As Steve said at the time he could not believe the difference in power....

 

Firthy

[chris_uk]

They do them off the shelf, but they aint cheap.  

  'Not cheap' being......?

Cant remember but more than the group buy price, and he mentioned at the time he wouldnt sell unless he fit them.

[chris_uk]

They do them off the shelf, but they aint cheap.  

  'Not cheap' being......?

Cant remember but more than the group buy price, and he mentioned at the time he wouldnt sell unless he fit them.

[JohnTurbo]

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.

 

 

Edited by JohnTurbo, 01 August 2013 - 05:18 PM.

[chris_uk]

its not good, expect to die... come on john..

[JohnTurbo]

Haha, i'm nothing if not childish!

If your car was balanced it was balanced - I'm certain youd notice if your back end overtook the front, but thats not my experience of it thats all.

Sorry Chris I hadn't read the thread and didn't mean to undermine you.

 

Too much front braking does little except put extra load on pads/fluid and makes you stop slower.

Too much rear braking is potentially dangerous.

- 2 pots all round, for instance, would be deadly. - Generally people uprate their front brakes only and its one of the biggest mistakes you can make, you always need to look at the whole picture, and allow for balance.

 

 

[chris_uk]

what i don't understand is how everyone but me seems to be having issues with the rears locking up.. seriously, i dont get it, i can stand on my brakes all day long and the front will more than likely lock first, if they lock at all.. i can bomb round my usual B roads and i am driving very hard and i stamp on the brakes and i get total compliance, not one hint of the rears locking.. what are the others doing so different which is causing locking?

[chris_uk]

can i just check.. these are the same as everyone elses right?

 

 

 

 

[JohnTurbo]

Oh btw, Phoenix's FTR brackets were 300quid. Last year anyway.

 

They look right Chris. Later type CP7600, asymmetric piston sizes.

Dont sweat it, since you have no problem leave it be.

It might be fairest to say that people should just be aware that they need to watch the rear bias and potentially take measures.

[speedster]

Oh btw, Phoenix's FTR brackets were 300quid. Last year anyway.

 

They look right Chris. Later type CP7600, asymmetric piston sizes.

Dont sweat it, since you have no problem leave it be.

It might be fairest to say that people should just be aware that they need to watch the rear bias and potentially take measures.

What about ABS? Will that not rebalance the system sort of?