Brakes suck
 

So I had terrible stock 1.6 brakes. They would lock up the front but not the rear very well. So I purchased and installed sports brakes. Now they lock up the rear but not the front. Used off the shelf cheap pads and got new front rotors. Rears were junk yard but in good condition.

I am suprised at how poorly I slow down. Maybe i am not used to the light car but my Jeep grand cherokee on oversize tire feels like it stops a lot fast. I just can seem to get it to feel like it is stopping fast.

Any suggestions. I know i will need better pads but they are the same brand and type front and rear.

I know the sports brakes have bigger rear disk than front is that my problem and would a proportioning valve fix?

Prop valve: http://trackspeedengineering.com/sto...kit-p-152.html
and HP + pads (as long as you aren't tracking it, doesn't sound like you are)

Prop valve so you can get your bias correct, pads for more bite (higher friction coefficient).

Front brakes do the lion's share of stopping the car. Rotors and pads work together. Crappy pads = crappy performance with rotors being equal.

Is this on the street or track? How's your brake fluid? Are your tires good?
The best braking system won't do very well with bad tires.

Recipe for excellent street brakes on a 1.6 car:

Stock 1.6 calipers and rotors (or NAPA equivalent.)
Stock 1.6 brake pads (OEM Mazda- no substitutions here.)
Tires that don't suck.

I have SE Sport brakes on my 01 and it stops like a friggen monster.
Seriously surprises me.
No idea what pads it has, probably good ones lol

Your bias is (currently) fukt

+1
I have them on my 99 with the stock 99 booster + 99 master cylinder, with ss lines, oem pads, napa rotors, and 205 wide dunlop dz101's, and it's very hard to lock up one corner unless I am doing something extremely stupid. Braking on the 1.8 brakes used to make me seriously nervous. It would take up 60% of my attention to keep them from locking up. Now it's something I don't even think about since they lock up all 4 wheels at the same time.

Check to make sure the rears calipers aren't frozen. If you forcibly push the pistons back on the rear calipers (and break them), will they stick? Or will they be loose? That's another thing to check. I'd get larger rubber too, like someone else said. But that won't help your bias. Also check your pads and if you run out of ideas buy an msm master cylinder. I've heard good things from those on m.net and there actually is a booster and mc for sale for $40 if I remember correctly.

I tried NAPA ceramic pads once - they would lock up the rears before the fronts, and I was literally still overshooting stop signs 6 weeks later - plenty of time for pads to get a good bedding in. Switched back to organic style one day after misjudging a stop sign so bad that my car stopped in the middle of the intersection - thank god it was on empty country roads. During my mini-renovation I called porterfield and had them ship out some R4S pads for all four corners - so incredibly predictable, it's nice to not have to think about braking again. Most cars (without abs) are designed so that the front tires lock up before the rear tires do - If your front tires lock up, you lose control of your car, but you will usually continue slowing in a straight line - you can regain control simply by letting off the brakes so much that the static friction between your pad/rotor is reduced to less than the kinetic friction between the tire/road. If your rears lock up, you will again lose control of your car, but you have a much higher chance of putting the car into a spin as the rear of the car tries to "get in front of" the front of the car. You can still regain control, but only to the point where your steering angle can match the slide angle of the car - once the slide angle of the car is greater than your possible steering angle, you're pretty much out of luck.

As far as "sport brakes have bigger rear than front" - no car should have larger rear brakes - that makes no sense at all to me, so obviously I'm missing something. The rears would lock up long before you would be able to get a good bite on the fronts - you would probably be better off with no rear brake vs. bigger rear brakes.

The rotors are larger in the rears 10.9 vs 10.8 IIRC. The pads are significantly smaller back to front, but the rear rotors are still larger. There's quite a few cars that are like this.
For example:
2012 MB c250 sport
Kia Rio 5
Chevy Silverado 2500 LTZ 4WD (not a fair comparison since they're made to haul over 17k lbs)

There's a bunch more, but I got lazy and ran out of magazines to look through.

This on the street. To be honest when i first switched it locked up the front first now its the rear. My brakes just dont slow me down the way I expect. I have good tires. Azenas. I prob misspelled that sorry. Lots of thread same size front and rear.

Maybe I did not seat them correctly. I did a autocross a couple days after install?

Where is the 40$ msm booster?

if i were to do it again, with my 1.6L, id do 10" 1.8L F and sport 10.9" R, with willwood valve and good pads.

Also:
Acura NSX
Toyota MRS
Lotus Elise (I think)

Rotor size is only 1 part of the equation though. Thickness, vented vs. solid, pad size, etc. all impact performance.

Brake torque = circuit pressure x piston area x effective radius x 2 x coefficient of friction

Thickness and vented vs. solid have no direct effect on torque. Pad size, as in surface area, may have a secondary effect, depending on the pressure sensitivity (linearity of response) of the friction compound used, but it would be very unusual for this to be meaningful between pads as similar as 1.8 rears and Sport rears.

The Sport rears gain more on the 1.8 rears by going from a 32 to a 35mm piston than they do by going from a 255-ish mm rotor to a 276mm rotor.

Sport fronts go from 50.8mm to 54mm piston, and 255mm to 269mm rotor, so the percentage increase in torque is less.

Hence, Sport brakes have more rear torque for a given hydraulic pressure distribution.

I had cheap pads on my car when I bought it. The cheap pads are worse than shite. Get OEM or a road/race pad then do a brake fluid flush.

I think that will resolve your problem...and you'll be saying, jeez my jeep just doesn't stop like my miata! :)

Man this is the first time I've heard of a miata locking up the rear first. I've got parts store ceramics in the front and ebc reds in the back and still lock the front first. My friend in CPS has 1.6 fronts and 1.8 rears with parts store pads all around and still locks the fronts first but just barely Though the 275 hoosiers are approaching 100 runs and he does have 3.5* of camber up front.

I have converted to 1.8 brakes and run XP10's F&R, withe SS lines, Willwood prop valve, and deleted brake booster with stock master. I run 205 50 15 Hoosier r6's. I was having issues with front lockup, and converted to Sport rear calipers. Before the caliper change, the prop valve was set full rear. Now prop valve is at about 1/2 way towards less brake. After tracking the car Saturday, I got good input from a friend driver, that said the rears were smoking in hard brake zones, I knew there was some lockup, but was not sure where. I have since given the valve another turn to less, and hope my already awesome brakes will be even better.

Just the sport rotor or sport rotor & Caliper?

maybe depends what was available. i think the stock miata, at least the 90-93, lacks a good rear brake.

Get some race pad ,my Carbotech work fine my DD. but except they won't last long.