So I am going to switch over to the GT-Four Calipers, front and back and I have a question to anyone who has done this. What did you do about the brake bias? I have the ST205 valve... but it is plumbed for ABS so it is not immediately compatible with my current configuration.... Of course this thing sits behind the engine so the decision has to be made before I drop the engine in....

Let me know your thoughts.

would you be able to wait this weekend for me to tell you about bias the result?
I will be taking the first drive with the full setup using the ST204 cylinder and booster

I don't think the new bias will be very evident. And if anything, it will be an improvement. That's just my ignorant presumption

If you are concerned with it, you can just install and Bias Controller and be done with the issue. Or change bias with using pads with different grip characteristics

As for your question about using the ST205 master cylinder, I know that people have been fine using the ST204 cylinder.

A larger master cylinder may not be necessary and probably wont help with the bias.

There are so many factors involved in brake bias and also reservoir volume and pressure. Ill break my fingers going on a rant so here is a thread thatll learn ya some things haha. The thread kind of tumbles into a volume and pressure math-off, but for the upgrade that he has gone to from stock is a bit greater than gt to gt4 brakes.

Unfortunately is raises alot of questions and makes everything a bit more complicated

http://forum.miata.net/vb/showthread.php?t=347440



EDIT:
looking back on this I am going to revisit some of this information after I'm off of work. I'm a little scatter brained with my posts when I am at work haha

This post has been edited by Tigawoods: May 14, 2013 - 11:08 AM

I got a little heated when I read through that miata thread haha the guy was using diameters for his area and volume measurements. And then I read his edit. All good now haha

But yeah, I'm swapping calipers (right now, actually) and didn't even think about the bias. I didn't have to worry about it in my RS when I swapped STi brakes to it. I hope it won't play a huge role.

Do the GT and GT4 brakes not have the same ratio front to back? (That's probably a really ignorant way to look at it, but it'd make sense to me)

I have both master cylinders here - I don't see any difference... my concern is only with the OE brake proportions / bias.... I am actually trolling pegasus racing right now to see what my options are... Obviously the correct play here is 2 master cylinders with a bias bar...

Gah I need to find a money tree.

im not sure what the native bias will be without any bias control, but with just a brake proportioning valve, you will be able to take away from the rear and add to the front, which is what I think you may be looking for as a result. (you cannot take from the front and add to the rear)

A prop valve isnt going to shave off a ton of bias, its more for fine tuning the native bias.
I believe the native bias with the new brakes will be sufficient with a little tuning of a prop valve


I don't think you need a 2 master cylinder setup. But that setup WILL allow you to change the bias more drastically, as apposed to just a prop valve. Race cars use dual cylinders! (not saying you cant have a racecar haha)

what are you trying to achieve? (maybe someone else can haha) but for me it is hard to calculate what you will need to obtain a "perfect" bias until you actually drive the car with the setup. There is no OE specifications for the bias that your car needs. The gt-four bias is different that what you will need and the bias that those brakes give on a GT4 chassis wont be what you are getting.

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Although I doubt they do, they could be somewhat similar. We need to do a test and produce some numbers!

This post has been edited by Tigawoods: May 14, 2013 - 12:57 PM

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I feel you think too much of me...

I am installing GT-FOUR calipers and rotors with grossly different performance metrics (not to mention the new car weight and balance) than the GT calipers and rotors... I would like something close to OE brake biasing so that I don't go ass before nose into a guard rail when I jam on the brake... It wouldn't be such a concern but the damn valve is not reachable when the engine is in.

I am not really trying to fine tune anything.. I am just trying to be proactive about the front / rear split of the brake circuits.... And really we (the royal we) don't know what the difference is.

when u are done, with the brake swap try to slam the brakes on a parking lot. i dont think anyone has real world info, it all will be guessed.

like right now. i have gt4 in rear and regular in front. Im still working on the front. and it does lock the back... i tried on empty parking lot.

>


yeah I got ya. This is definitely a decision that needs to be made prior to installing the engine

Do you have the calipers in your possession? You can start gathering measurements and come up with a estimate for you bias http://www.tceperformanceproducts.com/bias-calculator/

This wont take into consideration the weight spread of your vehicle or the pad bite, which can also affect to some extent.


ah, so you are using the GT-Four rotors in front, at least youll have an even diameter on all fours. I have 300mm in the front and 315mm in the rear which will throw a bit of bias to the rear.

I think with just 1 Master Cylinder (st204 will do since the other is plumbed for ABS) with no bias modification. Your bias will be a little high in the front, so plumb in a Prop Valve to even it out to more of a 60/40 ratio


am I helping at all or am I just jumping around? hahaha