JSchleim18
(Minor 69er)
05/02/11 11:37 PM
Pondering...adjusting brake bias

I have been doing some reading on brake bias and what would be ideal. It seems that our cars are heavily front favored. I was going to upgrade to the 3000GT VR-4 calipers. After reading that it can increase our front bias 16% higher, I wasn't too happy.

One way to bring some of the bias back to the rear is to run a more aggressive brake pad in the rear vs. the front. If you are using your car for track days, you would still get a race pad up front, but a more aggressive race pad in the rear. This will make it so the fronts aren't overworked.

Either that or I just stick with the stock 2-piston calipers for now.

Does this seem like a good idea (different compound rear pad) and does anyone have any idea how much of a percentage it will change?

Thanks all.


Olson
(Pwnd by Rance.)
05/02/11 11:39 PM
Re: Pondering...adjusting brake bias

Its worked before and I dont see any reason why i wouldnt work.

cheekychimp
(Director of Housing and Urban Development, and carbon/kevlar balls)
05/03/11 12:23 AM
Re: Pondering...adjusting brake bias

Jeremy, any idea on what the actual brake bias on the 3KGT is like? I know the 3KGT rear end swap has been flogged to death a bit recently but it is an option that would be far more effective in increasing your rear brake bias than just changing pads. That swap would allow you to run the 3KGT rear calipers which I am sure are twin pots.

jepherz
(Too Clean)
05/03/11 01:23 AM
Re: Pondering...adjusting brake bias

I can't think why different compounds front to rear would be necessarily bad, but I'm not sure you can derive any calculations or numbers by it. I have an upgraded rotor in the rear (larger diameter) with a caliper bracket and sold a setup to user Luke on here (I think). He knew his stuff on brakes and doing the calculations he said the rear setup was perfect for using the front camaro/cobra setup, which we both had.

AnotherNewb
(flutterdumper)
05/03/11 01:45 AM
Re: Pondering...adjusting brake bias

Not that I have experiance but... what about an adjustable proportioning valve? I see them in summit and jeggs all the time.

RedTwo
(Rangi Kiwi)
05/03/11 03:35 AM
Re: Pondering...adjusting brake bias

If you're really keen, you could fit an adjustable bias valve (well two of them at least) and fit them to whichever lines you want to decrease pressure in.

JSchleim18
(Minor 69er)
05/03/11 08:47 AM
Re: Pondering...adjusting brake bias

Quoting cheekychimp:

Jeremy, any idea on what the actual brake bias on the 3KGT is like? I know the 3KGT rear end swap has been flogged to death a bit recently but it is an option that would be far more effective in increasing your rear brake bias than just changing pads. That swap would allow you to run the 3KGT rear calipers which I am sure are twin pots.




IIRC, it was up around 78%/22% front to back. If I didn't POR15 and do the active toe elimination on my GVR-4 trailing arm I probably would have went to the 3000GT VR-4 rear trailing arm swap. The 2G 3000GT VR-4 came with 2 piston rear calipers.


JSchleim18
(Minor 69er)
05/03/11 08:49 AM
Re: Pondering...adjusting brake bias

Quoting jepherz:

I can't think why different compounds front to rear would be necessarily bad, but I'm not sure you can derive any calculations or numbers by it. I have an upgraded rotor in the rear (larger diameter) with a caliper bracket and sold a setup to user Luke on here (I think). He knew his stuff on brakes and doing the calculations he said the rear setup was perfect for using the front camaro/cobra setup, which we both had.




I saw the thread you created on the bracket...that would be great. I wonder if you could still make these . Reading Luke's information in THIS thread is what got me thinking. Also, the Camaro calipers had even MORE front brake bias. I wonder if the bracket will make me too rear biased?

As far as an adjusting brake valve, I want to avoid that route for the time being. If I can have a pretty slick brake setup without the adjustable valves, I'll be happy.

Thanks for the info so far.


alansupra94
(Excuse the retarded question.)
05/03/11 10:29 AM
Re: Pondering...adjusting brake bias

I mean I don't think an adjustable brake bias would be that complicated to make would it? I have seen a few small DIY floating around and I will be looking into it considering I plan on putting in some nice Wildwood (or similar) calipers to improve my braking performance.

Keep in mind that changing the bias can make things very crazy. Adding too much in the rear can cause instability especially in cornering.


JSchleim18
(Minor 69er)
05/03/11 11:32 AM
Re: Pondering...adjusting brake bias

^^^That is my concern. I don't want to be too rear biased and lock up the rears before the fronts. This is EXTREMELY dangerous. I just want to make the rears work a little more than they will be when the bigger brakes go on up front. I think making a bracket for a larger rear diameter rotor will help. I just need it to fit under a 16" wheel

alansupra94
(Excuse the retarded question.)
05/03/11 01:19 PM
Re: Pondering...adjusting brake bias

Yeah I mean you can easily just test the bias out and adjust in a very large parking lot. I would maybe go with a 70/30 ratio...anything more might be pushing it. There are tons on tons of books that I will try and read but from what I have learned from talking to various people is that there is like a billion variables. The only way to get your car running like you want is to get/make it adjustable and then play with it until you are happy or die

JSchleim18
(Minor 69er)
05/03/11 04:01 PM
Re: Pondering...adjusting brake bias

Orrrrr....I can use RX-7 calipers?

36.1mm piston area. 4 piston aluminum calipers (unlike the 3000GT VR-4 which are rigid iron). They came with 10.9" rotors but you could use 12.35" 3000GT VR-4 rotors with the right bracket. (JDM RX-7 Spec R came with 11.6" rotors and used the same rotors. the Spec RS/RZ came with 33.9 and 38.1mm pistons and used 12.35" rotors)

This is compared to 40.4mm and 42.8mm pistons from the 3000GT VR-4.

Doing this would probably work out to keep the brake bias almost factory Galant VR-4 or a *little* more rear biased?

I need someone smart to chime in


JSchleim18
(Minor 69er)
05/04/11 11:23 AM
Re: Pondering...adjusting brake bias

This is just some info I decided to calculate:

RX-7 front brakes:
4x 36.1mm piston calipers
2.65" pad width

300ZX front brakes:
4x 40.4mm piston calipers
2.76" pad width

3000GT VR-4 front brakes:
2x 40.4mm and 2x 42.8mm piston calipers
2.94" pad width

For argument sake, I am using 11.6" (295mm) and 12.35" (314mm) rotors for the calculations.

Using those rotors and the pad width, I got:

RX-7 effective rotor diameter: 8.95" and 9.7" respectively

300ZX effective rotor diameter: 8.84" and 9.59"

3000GT VR-4 effective rotor diameter: 8.66" and 9.41"

Applying these numbers against the stock rear 10.43" rotor setup I got: *Keep in mind stock setup is about 2.9:1 torque split...lower the number the more rear biased it is*

RX-7 11.6" brake setup: 2.21:1 - 23.79% difference favoring the rear brakes
RX-7 12.35" brake setup: 2.4:1 17.24% difference favoring the rear brakes
300ZX 11.6" brake setup: 2.74:1 - 5.52% difference favoring the rear brakes
300ZX 12.35" brake setup: 2.97:1 - 2.41% difference favoring the FRONT BRAKES
3000GT VR-4 11.6" brake setup: 2.84:1 2.07% difference favoring the rear brakes
3000GT VR-4 12.35" brake setup: 3.09:1 - 10.66% difference favoring the FRONT BRAKES

Now I wanted to see what it'd be like to run a larger rear rotor to affect the brake bias.

I used the factory 3000GT VR-4 rear rotor dimensions for sampling. They are 11.18" (91-93) and 11.6" (94+)

First lets do 11.18"

RX-7 11.6" brake setup: 2.02:1 30.34% difference favoring the rear brakes
RX-7 12.35" brake setup: 2.20:1 24.14% difference favoring the rear brakes
300ZX 11.6" brake setup: 2.52:1 - 13.10% difference favoring the rear brakes
300ZX 12.35" brake setup: 2.73:1 - 5.86% difference favoring the rear brakes
3000GT VR-4 11.6" brake setup: 2.61:1 - 10% difference favoring the rear brakes
3000GT VR-4 12.35" brake setup: 2.83:1 2.41% difference favoring the rear brakes

Now the 11.6"

RX-7 11.6" brake setup: 1.94:1 33.10% difference favoring the rear brakes
RX-7 12.35" brake setup: 2.11:1 27.24% difference favoring the rear brakes
300ZX 11.6" brake setup: 2.41:1 - 16.90% difference favoring the rear brakes
300ZX 12.35" brake setup: 2.61:1 - 10% difference favoring the rear brakes
3000GT VR-4 11.6" brake setup: 2.49:1 14.14% difference favoring the rear brakes
3000GT VR-4 12.35" brake setup: 2.71:1 6.55% difference favoring the rear brakes

It seems as long as my info is correct, RX-7 brakes will be almost too rear biased. Their clamping force was also calculated at 2.14 as opposed to 2.68 for the 300ZX and 2.84 for the 3000GT VR-4 (stock is 2.8).


jepherz
(Too Clean)
05/04/11 12:41 PM
Re: Pondering...adjusting brake bias

Don't you need to take into account the stock prop valves of each though too?

JSchleim18
(Minor 69er)
05/04/11 12:49 PM
Re: Pondering...adjusting brake bias

I guess I should say these are estimates based on the formulas in the 3000GT VR-4 brake upgrade how to

jepherz
(Too Clean)
05/04/11 01:25 PM
Re: Pondering...adjusting brake bias

Well, I don't see any mention of any prop valve, am I just missing it? Again, I am not sure how a factory prop valve works either. I've heard that it is just a 50/50 split until a certain point, in which it starts to bias more towards the front but who knows if that is correct. With an aftermarket adjustable master cylinder, you'd get the same split going to the front/rear no matter how much you were pressing on the brakes.

JSchleim18
(Minor 69er)
05/04/11 01:51 PM
Re: Pondering...adjusting brake bias

The prop valve does what you said...it stays 50/50 until a certain point and then more pressure gets applied to the fronts. This will stop the rears from locking up. My calculations were done with no factors or conditions in place. It should help anyone who wants to keep a relatively stock torque split.

RedTwo
(Rangi Kiwi)
05/04/11 09:02 PM
Re: Pondering...adjusting brake bias

Nissan 4 piston calipers are 4x40.4mm, so a slight decrease from the GTO - They normally run ~280 dia up front, and if you find some GT-R calipers (same pistons but wider discs) you can run larger ~320 Brembo rotors or anything custom made.
Are you talking FD or FC RX7 brakes?


JSchleim18
(Minor 69er)
05/04/11 11:35 PM
Re: Pondering...adjusting brake bias

you know, I was looking at the Nissan brakes (300ZX 90-93 are aluminum 4 piston...later models are iron). I was thrown off by the "26mm and 30mm ID's". I thought it was piston diameter but it was really for the rotor width.

I'm calculating them now.

The RX-7 calipers are the same internally between the FC and FD...the castings are different.


JSchleim18
(Minor 69er)
05/05/11 09:26 AM
Re: Pondering...adjusting brake bias

Updated the post to add 300ZX calipers. There are 3 different sets of calipers in the US:

The "26mm Aluminum" calipers were used ONLY on 1990 non-turbos. They used a 280mm x 26mm rotor.

The "30mm Aluminum" calipers were used on 1990 Twin-turbos and ALL 1991-1992.5 300ZX's (both turbo and non-turbo alike). They used a 280mm x 30mm rotor.

The "30mm Iron" calipers were used on ALL 1992.5-1996 300ZX's (both turbo and non-turbo alike). They also used the 280mm x 30mm rotor.


RedTwo
(Rangi Kiwi)
05/05/11 09:01 PM
Re: Pondering...adjusting brake bias

So you're not considering the FD3S RX7 'small' Brembos?

JSchleim18
(Minor 69er)
05/05/11 11:51 PM
Re: Pondering...adjusting brake bias

I haven't heard of them having Brembo's from the factory...just Sumitomo. The RX-7 Type RS/RZ came with 33.9mm and 38.1mm pistons which were roughly the same area as the 36.1mm pistons. They, however, had 314mm rotors and larger wheels.

RedTwo
(Rangi Kiwi)
05/06/11 08:02 PM
Re: Pondering...adjusting brake bias

Sorry, I got my brakes mixed up I was thinking of the R32/3 GT-R brembos - 38.0 & 44.0mm.


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