With these calipers now being stupid cheap (45$ each), I bought a set. Will be running the weak sauce 0.810" discs cause street car with narrow wheels. Hopefully they will fit under my Watanabes; quick CAD based on (allegedly similarly sized) superlites says so. Waiting for them to get here before making adapters. Wondering if Supermiata (or any other available and reasonably priced) hats will work with these and UL32 rotors.

 

They're so stupid cheap I'm tempted to buy a set just to hold on to in case I ever want to go 11.75. I am sure once they're NLA you could sell them on here for what was paid.

 

they are stupid cheap. Speedway has "a lot of them" in stock, at 45.99 each if the part no is just the 6630040 (which is symmetric and just fits both sides?) Sort of embarrassed by my ignorance - but they list lh and rh for F88 also.

Thx

Wombat

 

The stupid cheap version is not the one that works with Brofab’s BBK. The piston diameters are wrong.

 

The side specific ones have staggered pistons to reduce pad taper wear. The leading piston should be smaller, if I remember correctly.

The ones that are not side specific have identical piston diameters across all four pistons.

I purchased the 0.81" rotor, 1-3/8" and 1-1/4" staggered piston caliper that is side specific. They are $45 on Speedway. part #s 6630051 and 6630061. The 4x 1.38" piston option was still available last I looked, but at $70 a caliper on the Afco main site. Theoretically, it is a closer match for the standard 1.8 brakes in terms of hydraulic area.

I did this after speaking with Bronson, hopefully I didn't get the wrong impression of what to buy from him.

Based on my rudimentary excel math, I should be able to get a combination of standard Miata parts in the rear that gives good bias with the lower hydraulic area of the staggered piston caliper. I might end up with a Sport caliper on a 1.8 rotor and bracket, or vice versa. Relatively smaller caliper hydraulic area should give me a stiffer pedal as well, an added bonus.



Since I have Sport brakes, the bias change is calculated from that. It only takes into account hydraulic area and rotor outside diameter.

 

I would use area and effective rotor radius (middle of pad, as pad height is different). I got the staggered ones as well; I believe they are also available in 1-7/8 & 1-3/4 but these have a much larger piston area that will move the bias too far forward with stock rear brakes.

 

Absolutely true for a real calculation of brake torque!

Given the rough nature of these calculations, I figured the rotor OD was a close enough stand in. All I did was use the OD ratio of rotor diameters as a multiplier on hydraulic area. I'm only looking to do is get in the right ballpark for choosing major components, then I'll fine tune with an adjustable prop valve.

I do want to get the pre-prop valve bias right though, so that I'm getting the most out of the brakes and getting good balance not just at lockup limit braking, but also trail braking into the corner

 

Big piston first to engage the rotor(leading). Smaller piston second to engage the rotor(trailing). Less force applied to the hotter part of the pad.
As mounted in a Miata, the big piston should be on the bottom.

 

Thx guys! Cats on the way.

 

You would have to play with M/C sizes to do that IMO... Lots of work for "little" gain IMO.

All your adjustment is going to be in the rear prop valve.

Fronts get full pressure/full volume, whatever that is your M/C puts out based on bore size... Then you adjust for rear.

Yes the traditional way of setting rear bias is through lock up testing, but thats not the be all end all of how to set a prop valve. Thats just the "limit" so to speak.

If you are running a booster, I would go to a 1" M/C. Non booster, 7/8". The 15/16 is a bastard child size IMO.

Im running non booster, 7/8" M/C, Brofab big brakes front, sport rears, wilwood prop valve. Right now my rear prop valve is 2 turns in, but I am still playing with it.