Front to Rear Brake Bias

Suspension, including wheel, tire and brake.
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BrandonS
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Front to Rear Brake Bias

Post by BrandonS » 02 Apr 2019 09:25

What do you guys with upgraded brakes run for a built in bias between front and back? I'm trying to decide on my rear calipers, but want to make sure I don't over bias the front and run into overly hot brakes. I'm also hesitant to jump to a near 50/50 biased setup and rely on a proportioning valve if that is not appropriate. I feel inclined to aim for 60/40 front to back and add a proportioning valve if necessary.

Would love everyone's input and experience. I feel after all the measuring and planning out a couple setups with different ratios, your input would be nice to help me make a choice.
Last edited by BrandonS on 02 Apr 2019 16:57, edited 1 time in total.

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bertvorgon
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Re: Front to Rear Brake Bias

Post by bertvorgon » 02 Apr 2019 15:10

In my case, I have the 280ZX master 15/16, with 4 piston Brakeman calipers up front. Rear are the BMW 2002 front 4 piston calipers on the rear.
In the drivers cockpit, next to my seat, mounted on the passenger side of the trans tunnel, is a DIRECT CONNECTION brake bias. This one is a rotatable knob that has a bit more of a lineal adjustment, than some that have the four or five "detent's".

I have a full range in terms of getting the back to lock up before the front no problem. Or vise versa.

Don't forget to have a half tank of fuel or whatever combo in the car, as the weight can make a difference. Brake pad and tire choice are a factor also, specially as everything heats up...it CAN change a lot.

What I did, was decide two things..RACE mode...street mode..for having my "range' then made note of how many turns to one or the other.

This is where it does get a bit hard, find a nice SAFE place to get to whatever speed you THINK you MIGHT be hauling the car down from..REPEATABLY. Then, you need to be sensitive to incipient lock up...ONCE you have HAD lockup..as this will be the "balance" setting for the bias...you back the bias in or out depending on what you want happening.

I agree with more of a front bias, as I'm a wimp and do not want the rear to lock going into a turn where the one un-weighted corner gets light, locks and can require some hero moments on the steering wheel or just is not doing it's job of slowing the car.

Get it right and you can always trust your brakes in most all situations.

I ran my brake line down the tunnel, where it normally was, then popped it out to the passenger side into the adjusters, then right back into the tunnel. It was a bit of work, but, when I was racing, it was nice to have it at hand as situations change.

That being said, since I am only driving on the street now and make it my mission to NOT use my brakes, I have not touched that adjuster in 20 years now.

And yes...the passenger seat does fit in.
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Direct Connection bias adjuster
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Keith Law
1973 2Door Slalom/hill climb/road race / canyon carver /Giant Killer 510
1968 Vintage 3HP Mini Bike
1971 Vintage 13' BOLER trailer

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cartel
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Re: Front to Rear Brake Bias

Post by cartel » 02 Apr 2019 19:59

Keith
do you know what sizes your pistons are F + R ?
im just doing some math today for square inch on caliper/ piston sizing and dont want to go to big . i was thinking 1.12" on the rears and 1.5 on fronts -- possibly 1.38 front..
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Datsun: 71 dime; 73 Z ; GT3 240
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bertvorgon
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Re: Front to Rear Brake Bias

Post by bertvorgon » 03 Apr 2019 09:38

Morning Gang!

At the front, I have the Brakeman F3 caliper with 1.750" pistons (4)

I believe the BMW 2002 4 piston calipers have a 34 MM piston.

Do not forget that I put a 2" extension into my brake pedal, which very nicely increased the leverage and made modulating the brakes just excellent.

As a point of reference, considering I have proper front rotor cooling, this combo let me survive 1/2 hour sessions at Mission, on the old course, with Motul RBF 600 brake fluid. A final option would be water spray in the cooling duct. I never did that as our track days ended but Specialty runs that on all their cars.

At the point that we did the BMW rear calipers, there was not much out there ( early 90's) so the BMW caliper was a good choice, due to the availability of a variety of pad compounds. That also holds to this day,so I was able to match pads for good brake balance. That is also key to being able to adjust brake bias.

Another thing I thought of last night, one must be aware of.....is weight transfer! The harder you are braking, as the pad(s) ramp up in temperature, has massive weight transfer to the front...thus making the rear lighter and the front hotter. I guess what I am trying to say is getting that FINAL balance that works, so the REAR is actually really working by DECREASING some of that weight transfer to the front, takes some practice and finesse. Also depends if you are going to brake as under race conditions. I can say that in all our years of some very high performance, FAST canyon carving, late braking that would create some serious heat going into a hairpin, is a rarity.

Our cars are light and with my combo I have more than enough brake for today's real world driving.
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"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan

Keith Law
1973 2Door Slalom/hill climb/road race / canyon carver /Giant Killer 510
1968 Vintage 3HP Mini Bike
1971 Vintage 13' BOLER trailer

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Byron510
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Re: Front to Rear Brake Bias

Post by Byron510 » 03 Apr 2019 22:42

A slightly more extreme option, when I painted the Bronze I did only two modifications, I installed a roll cage and I upgraded to a top reverse mount pedal box to get adjustable brake bias. At the time, the car actually still ran stock brakes! But I knew upgrades were imminent, I just wasn't positive on which direction at the time, and it made sense to make the bias adjustable moving forward.

The green arrow points to the remote bias adjuster connection, which led via cable to an adjustment knob right beside the seat. This set up is infinitely adjustable from 25/75 to 75/25 percent. Out side of this range, you step up/down to a different MC size, making the set up nearly infinitely adjustable no matter what you run front and rear fro brakes.
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Here's a shot of the car 10 years later, showing the adjustable bias knob location;
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And BTW, the stock dash complete fits unaltered and the factory side air vents were unaffected, glove box and factory 69 SSS dash cluster utilized.

This mod in this form pictured would interfere with the stock heater box which I didn't plan to install (a mistake in the PNW!), but I have since done two similar installations that had the stock heater boxes installed - takes a bit of time fitting, but it can be done - and without a cage.

Byron
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because the opposite never works.

BrandonS
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Re: Front to Rear Brake Bias

Post by BrandonS » 04 Apr 2019 11:00

Thanks for the input everyone. I'll let the stuff sit in my cart for a little bit yet as I mull it over. The reason for peicing it together myself is because there isn't a kit that checks all the boxes for me. I want to keep my 14" wheels, fit a decent sized rotor inside them, utilize my 200SX struts I already have, and if possible have an integrated parking brake.

It's a lot of wants, but I think I've sorted out a few setups that will allow me to do it. The options go back and forth, but I end up with anywhere from a 65/35 front/rear bias to a 75/25. I'm having a hard time choosing between two setups. The 65/35 or a 73/27. The 65/35 doesn't offer any greater clamping force over my current single piston 200SX brakes, but does offer more pistons in the caliper and a larger rotor. The 73/27 offers greater clamping force, larger rotor, more pistons in the caliper but I'm not sure if that bias is too far forward.

I may just call Wilwood and talk to them and see what their opinion is. I don't want to make the wrong choice because changing a setup wouldn' t come cheap.

EDIT: After some more reading, it doesn't seem like the 73/27 is far off from normal specs on vehicles.

BrandonS
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Re: Front to Rear Brake Bias

Post by BrandonS » 05 Apr 2019 13:35

So called Wilwood. They didn't have much advice to offer. I think they don't want to recommend a bias number due to legal reasons which I can understand. I did work with a couple more calculators though. Between the three of them I was able to get an estimate of what the dynamic braking loads should look like. Just posting for anyone else who may need some help.

This one does static bias calculations. If you do the calculations you can use the piston areas it spits out for the other calculators...
http://www.tceperformanceproducts.com/bias-calculator/

This one is geared toward Miatas, but in my case the equipment I was looking at using had very close to the same piston areas/rotor sizes as what was listed in the drop downs. I was able to use this after calculating piston areas on the setups I was looking at and then selecting a drop down option that had very similar areas.
https://www.blackartgraphics.com/pages/ ... bias-model

Then I used this one as well; I guess just to verify the numbers above. Since you can change different paremeters you'll get different numbers for dynamic bias, but it's nice because between the two you'll get an "effective" range to figure out if your selection of parts is at least in the correct ballpark. This also has a piston area calculator on it.
https://brakepower.com/

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