legend4life

Ha, just realized that probably doesn't work due to different fitments.

But I meant just trying the compounds on opposite ends, ie XP10s in the rears.

sjmarcy

Front serving prop valves are generally not a good idea. There is a modulation concern related to hysteresis and friction in the prop valve.

More capable rear brake hardware would help fundamentally.

I've installed full sport rears onto earlier Miatas with great results. Around 30% more rear braking action leads to stronger braking overall along with markedly better trail braking capability. It also reduces some of the workload up front.

If you are rules or wallet limited pad swapping comes to mind, however the bias shift varies with conditions.

k2-

Anyone have any guidance for installing the prop valve? FM kit?

sjmarcy

NA with 1.8 front and NB Sport Rear brakes:

bellwilliam

iTrader: (1)

I will double check with Emilio next time I see him. he recommends XP10/8 on most Miatas w/o prop valve, and that combo is the most popular Spec Miata setup. but he also recommends same compound front and rear, which is what I run on my Rotrex Miata.

curly

iTrader: (25)

Search around, a few of us have done it different ways. FM's kit is by far the cheapest and easiest way to put in a proportioning valve. I'm not going to lie, some of there stuff is a little spendy, yet this kit is only charging you $28 over the price of the valve from a place like summitracing.com, and for that you're getting 3 custom made adapters to take all the headache and tube flaring out of the project. 28 dollars VERY well spent.

Check out my build thread and Keith's Targa build for an in-cockpit mounting option, otherwise follow FM's instructions to mount it in the stock proportioning valve's location.

P.S. You're doing okay for a newb but you're also bumping a few slightly old threads, try to search a little more. If it's a "dead" thread (older than a couple weeks), the original question has most likely been answered. Make sure to fully read and comprehend the entire thread and check out any linked sites/threads/pictures.

Braineack

iTrader: (62)

just be careful with those damn fittings. let's just say I need another one.

k2-

Thanks Curly. I think I have seen what you're talking about on the Targa build site...remote **** mount looks nice. Been up in the air with this mod in general for street car (daily drive) due to changing tires for track and then street again / setting the prop. Don't want to find the rear end in front of me on the 405. Would need to be diligent about it is all.

chpmnsws6

iTrader: (12)

Which one do you need?

Braineack

iTrader: (62)

the metric to sae ones that FM make.

comradefks

iTrader: (3)

I know this is an old thread but I wanted to bump it up because I am in a similar situation with my brakes, other than the having already installed an adjustable prop valve part.

Current brakes on my '90 are 1.8's all around with the XP10/XP8 combo. 1.6 Master/Booster/Prop valve. The car is very difficult to trail brake with almost any steering input. For the SoCal guys, squirrely into Off ramp and the Sweeper on CW13 at BRP.

I'm wondering if putting in a 1.8 prop valve will help me out? Was recommended this by an SM driver at BRP one weekend but haven't really confirmed it. Also, have heard of people removing the spring in the OEM valve all together to have the pressure linear to the rears all the time. Does this work?

Overall my braking is good, in a straight line. Just trying to see if I can get the car more planting in trail braking situations. Often feel like its making taking the correct line through a corner more difficult.

Thanks guys.

Braineack

iTrader: (62)

get an adjustable prop valve and XP12s for the rear.

comradefks

iTrader: (3)

Is this typical to run a more aggressive pad in the rear versus the front? Is it to offset the lack of capacity in the rear brakes? Just goes against the typical XP10/XP8 combination. Thanks.

Braineack

iTrader: (62)

its not typical. We are still undoing everything that SM incorrectly did to us that and years of m.net engraining things into us.

I'm sure many others will disagree, but in my experience the miata needs help with rear bias...


Two things I know for fact:

With similar sized rotors F/R and even pads, the car needs more rear bias.
With upgraded front rotors and even pads, the car needs more rear bias.

Alta_Racer

iTrader: (4)

The fix for me was sport rear calipers, with a larger piston, XP10's F&R. The prop valve lets me dial in for conditions now.

The XP10 front and XP8 rear is not at all correct imo. 10's front and 12's rear maybe.

psreynol

Ive not run carbotech stuff for several years but they had my pad of choice for many years but Ive never run the xp10 on a miata. I would consider trying a xp8 up front be because xp10 seems pretty aggressive up front however It should be fine if that was recommended

when you say you need more rear bias, what exactly is happening to make you say that?

you are only running 205 up front

what suspension do you have?setup? suspension can have a profound affect on braking performance.

comradefks

iTrader: (3)

My thought is I need more rear bias. Car gets very unsettled during trail braking where the back end will come around if I brake too hard or turn too much while braking. The handling of the car is very neutral otherwise in both high and low speed corners. Current setup below.

Koni Sport w/ FM springs
FM front sway, 12mm OEM rear sway
205 RA-1's
Front Alignment: -2.25 camber, 0 toe, 5 caster
Rear Alignment: -2.5 camber, 3/32 toe in
1.8 Brakes with XP10/XP8 combo and Centric blanks

psreynol

my understanding of the bias controller is that it it does not increase pressure over what is available so the most bias you can get in the rear is equal to the front. so you need bigger rear rotors, more aggressive rear pads or less aggressive front pads. based on those temps you sited i would personalty try a less aggressive pad up front. Im sure the recommendation was sound but sometimes an overly aggressive front pad is just about the worst thing ever if you are hammering hard.

suspension is also a factor, what is your ride height front and rear? measured from where? a free option is to perhaps raise the front a little or drop the back. if suspension is good I would just get different pads up front.

comradefks

iTrader: (3)

Would removing the spring in the stock rear brake proportioning valve basically make the pressure sent to the rear brakes linear? No knee point.

If so, would that be the same thing as a Wilwood valve turned all the way to "more brake"?

Braineack

iTrader: (62)

correct. you can go from 100% of the pressure to 57% of the pressure.


btw, what size are the miata brake line nuts? 10mm? seems like wilwood sells a prop valve drill for 10mm bubble flare nut/tubing.

would be nice not to have to use brass adapaters.