Brake Bias Questions
11-21-2018, 06:42 PM
Post: #1
Brake Bias Questions
Hi Guys Smile

I have a predicament.
I'm running FD3s Calipers on the front with Mini Cooper S Discs but standard AE86 discs on the back.

I was planning on running a high Mu (Project Mu HC+) pad on the back that bites from cold (as I'll be using it for drifting) but I also plan on doing the odd track day in it, so need a pretty good pad up front.

Front tyres will always be a Group 1B/S tyre so tyre grip isn't really a concern.

My concern is, if I go for the same pad front/back, it might be too aggressive on the front for track (helps to pivot the rear if drifting though).

So, I thought of my options.
A - Run the same pads front/back but put in a Bias adjuster.
B - Run slightly less bitey (Ferrodo DS2500) pads on the front than the back to balance out the braking a bit.
C - Run slightly less bitey pads on the front than the back to balance out the braking a bit BUT with a brake bias adjuster too.

Any experience would be really handy Smile

Many Thanks,
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11-21-2018, 11:19 PM (This post was last modified: 11-21-2018 11:19 PM by Project D.)
Post: #2
Brake Bias Questions
OEM: 68/32%
RX7 caliper + mini discs: 72/28%

Note: that's without taking into account the original proportioning valve (that limit the pressure on the rear) and with pads with the same µ F/R

Also, "Bias adjuster" (the knob that control a balance bar) is only available on pedal box (independent master cylinder per axle)
Proportioning valve and bias adjuster are totally different things and have a different purpose.

Personally I wouldn't bother. The faster you go the more front bias you need, so having less braking force on the rear shouldn't have any hill effect especially with good tires.

Now if you absolutely want to get close to the original brake balance, the best option would be to go with bigger discs on the rear. (require custom brackets)
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11-22-2018, 10:06 AM (This post was last modified: 11-22-2018 10:16 AM by totta Crolla.)
Post: #3
Brake Bias Questions
If you install a way to adjust brake balance then ideally you need to run the same pads front and rear. If the pads act differently when they change temperature you will be forever chasing your tail adjusting the brake balance.
The only real way to adjust brake balance is with a balance bar pedal box.
You could try same pad front / rear but remove the standard proportioning valve and fit a decent (AP) driver adjustable one in its place. I use this on my rally car and it is a good compromise to a bias pedal box. (Rules don't allow a bias pedal box for me)

An analogue brain in a digital World
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11-22-2018, 07:10 PM
Post: #4
Brake Bias Questions
Thanks guys Smile that really helps!

Sounds like same pads and work back is the most reasonable way around this.

With regards to the Bias/Proportioning question, what IS the difference? I always thought they were interchangeable terms.
Does proportioning just work by limiting the output pressure (compared to input pressure) of the rear brake circuit in comparison to the front?
While Bias is adjusting the pedal input pressure over a %output split across 2 individual cylinders?
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11-22-2018, 07:46 PM
Post: #5
Brake Bias Questions
From a driving point of view a bias pedal box is more consistent, from my experience a proportioning valve limits the pressure of the fluid but as expected is sensitive to the speed of the brake pedal application.
Here is an interesting article:

An analogue brain in a digital World
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11-23-2018, 01:25 PM
Post: #6
Brake Bias Questions
Thanks for sharing Smile certainly clears a few things up!
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12-06-2018, 01:22 PM
Post: #7
Brake Bias Questions
Hey mad,

What i have done...

Some brembo rotors in the front with projectmu NS400 and DIxcel PD in the rear OEM size with PMU HC+.

The brake handling is insane... For a perfect tune-up i would need to push the material specs in the front.. as the oil boils after a few laps on the track.. Smile

I would go for some DIxcel Rotors and a HC+ to complete my brake package! Smile
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12-07-2018, 11:09 AM
Post: #8
Brake Bias Questions
Some would argue that having the fluid boil is an indication of a bad brake set up, not a good one

An analogue brain in a digital World
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12-08-2018, 02:50 PM
Post: #9
Brake Bias Questions
You may have water in the brake fluid [boils at a much lower temp.] I would first try replacing "all" the brake fluid. Only use a new can of brake fluid. You could also look at ducking air towards the disc/caliper. You maybe able to bend the gravel shield out to scope air and/or remove it to improve air flow, if you are allowed to modify it. Dave W
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01-02-2019, 04:17 PM
Post: #10
Brake Bias Questions
For the rear you can use Primera P11 brake discs (direct slap-on) with Golf MK.4 calipers (direct slap-on), nice little upgrade, google it Smile

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