brake bias for cadillac caliper swap and other BBKs
 

wrote my first article on kinja comparing some of these kits and their bias changes with my best effort info:

http://sickmint79.kinja.com/ats-and-...390.1472560687

Rememeber, the stock system intentionally has a "little extra" rear, intentionally, so that VSC can function.

I wish more people thought their decisions through like this.

so between the two wilwood options (front only, no rear), 4 piston is better?

a buddy sent me this page after he saw the article: http://www.ft86club.com/forums/showthread.php?t=32594

wilwood had this to say: http://www.ft86club.com/forums/showp...6&postcount=18

although i don't find that comment very satisfactory.

per http://forums.nasioc.com/forums/show....php?t=1265631
the BRZ front rotors are 294x24 or 295x25.5

per http://www.ft86speedfactory.com/wilw...g#.V8uadPkrKUn
the 4R WRX rotors appear to be 305x20.5. i will let someone like CSG Mike comment on that, as others noted that seems rather thin. so i suppose there is a real question of how much improvement this kit actually gives you in thermal capacity, for the BRZ or WRX. (certainly more for us being 400 lbs lighter though.)

OP initial track impressions -
http://www.ft86club.com/forums/showp...0&postcount=71
http://www.ft86club.com/forums/showp...8&postcount=72

it would be cool to have some track temps.

some later impressions -
http://www.ft86club.com/forums/showp...9&postcount=76

those are simply not speeds i am running locally.

he appeared to eventually go to the 6 pot with a larger WRX rotor with OEM 86 still in the rear. i didn't see anything about a prop valve so it would seem this would have shifted bias forward a lot.

http://www.ft86club.com/forums/showthread.php?t=63636

I would like to mention that RR Racing also has a 6 piston Wilwood BBK (stage 1 & 2) which they claim to have tested and refined for proper brake bias on our platform. they're reasonably priced as well for $1000 a set. they do state to run more aggressive pads in the rear though if you're only running the front BBK. it seems to be a good option for the price to performance ratio if you're in the BBK market. however, for the majority of us, just upgraded pads and fluid will do the trick unless you want that bling factor lol.

^^^

I've got the RR Racing stage 2 BBK with BP20 pads. When using PMU HC+800 pads in the rear, there seemed to be a lot of front bias. I could hear/feel the front tires lock up early in braking zones. Switching the rears to Carbotech XP10 pads seems to have returned the brake bias to normal. Also appears to have taken a significant load off the front brakes overall (less wear, smell, etc.) I definitely think the kit works better with a more aggressive pad in the rear.

That said, theoretically... I wonder if you want brake bias to be pushed slightly forward on sticky track tires. Under hard braking there should be greater weight transfer to the front (relative to a stock tire for example).

i see lots of option at RR
http://www.rr-racing.com/Front-Big-B...gt86fbk001.htm

although i don't see anything about caliper piston sizing. it would be cool to add them if i can collect the info.

chat with them directly. updated! a lot of really nice options from them!

Great article. Glad more people are thinking about bias. When I did the calculation for stock a while back I got 65/35 assuming equal friction pads front and rear. I put on Raybestos ST45 front ST47 rear early this year which should have put bias closer to 60/40. I've been very happy with them. Only 2 track days at Barber and 2 AXs so far, but I have lots of confidence with the brakes. I haven't felt anything that makes me think I went too far rearward with the bias. One reason I did this was lots of people talking about the front brakes overheating. No hint of overheating and changing pedal feel at the track days at an intermediate pace. Hope to do a track night at AMP later this month. The brakes feel great on drives in the mountains. There's great modulation. I don't seem to have any problem getting just the amount of force I want when carrying the brakes into a corner. When simulating a panic stop, the fronts still get ABS activation with no hint that the rears are. I may have felt a hint of tail wag a couple different times when on the brakes in a slight turn on a road that had some loose sand/gravel. I had read of guys getting great pad life from Raybestos ST43 pads. Hoping that these are the same, because they aren't cheap. I'd get them again in a heartbeat though. I'm actually interested in trying out the cheaper Wilwood WRX 4 pots for the weight savings. I bet they'd work well for me with proper pads front and rear.

does anyone actually have the piston size from the RR kit or is it still just taking their word for it?

I hear the WRX 4 pots move the BIAS to the rear as wheel, does that make them a better option?

When I checked into it (Wilwood WRX 4 pot kit) a few months ago I calculated that it moved the bias forward about 2%.

Thanks

Sounds like it would be ok if you balance the pads a little. My other option was STi front's only. I think the stock rears are quite capable.

RR IS reasonably priced. And their bias seems no that bad off as some of retrofits. BUT - if even vendor says that for proper use one needs to use different pads front-rear, i translate it "we didn't care about getting right bias, so use this hack to workaround" putting big red sign against considering them. I get if such hack is used for retrofits, i get it if used for non-standard aero / staggered wheel & tire setup .. but NOT if for standard set marketed for most cars, without clearly stating if it's for some specific setups.