Road Race s13 Brake Options

[drbmw2002]

Just thought I would post something to pick everyone's mind. I currently race an s13 with SCCA in E Production. They finally changed the brake rules and allowed us, at a weight penalty, to upgrade from stock brakes. My biggest problem with the brakes was I was going through the pads at a pretty good clip......thank heavens for Carbotech's contingency. I know Def sells a front kit and I was hoping for the easy button. Of course the brake rules changed but the wheel size did not, 15x7 (I remember when 15x7 seemed like such a big wheel, haha). So none of the "big brake kits" would work. So after talking to Wilwood, they laughed at all the SCCA Production drivers calling them the past two months, I decided to go with a Dynalite and 11 inch rotor, same combo they already make for the MIatas. Anyway had to make my own hat and then a brake caliper bracket. At any rate, my question for people who have played with these longer than I have what did you all do for the rears, if anything? Right now after talking to Wilwood I am tempted to leave everything the way it is, just use the "bigger brakes" up front and leave the rears stock. However, since I have to take the weight penalty I was just curious to see if there are any other alternatives out there. Thanks in advance.

Dan

[Def]

Rear Z32s might fit under 15". I think it's a ~11.6" rotor or so? The caliper is pretty compact so there's a good chance it'd fit. That's a bolt-on and go setup, and probably about the same weight given the caliper is probably half the weight of the stocker or less. The Z32 e-brake is heavy (6-7 lbs per wheel), so if you need an ebrake, I might just keep running the stockers.

I think there was a combo of Z31 caliper bracket and later Altima rotor that got you at least a bigger disk. Not sure how much that buys you on track - I'd think going vented would be the biggest thing.

You could also go with a J30/Q45 rear brake setup as those all use the exact same upright. Would need to drill for 4x114.3 mm if you've got stock hubs. I think those are vented, steel caliper. Probably using a cable ebrake on some?

J30's came with 15" wheels I'm pretty sure from what I remember in my junkyarding days, maybe even Q45s.

[drbmw2002]

Thank. Don't need an e-brake so that's not an issue. Since I upgraded the front and have to take the weight penalty just looking to maximize the effort. I am running the stock hubs and considering I have 3 sets of 4x114.3 wheels no chance of me ever changing. I am glad you told me about the weight between the z32s being comparable even with the bigger rotor, I just assumed they were heavier. Like I said earlier after running 13x7 wheels for so long on my BMW 2002 I thought the 15x7 would be huge, haha.

[Def]

I ran Z32s on my car with the front Wilwoods. They're really nice aluminum 2 piston calipers from the era, and the pads are a little thicker so you'll get some more pad life. On an E-prod car you can probably run something like a Stoptech 309 Sport.

Can you run an adjustable proportioning valve? I think it's really worth it, especially if you run in the wet, as it's typically very difficult to get the bias to perfectly match over a wide range of decel/tire grip ranges. You actually want more rear brake in the dry at say 0.6 G vs. the same braking in the wet given that tire load sensitivity changes in dry/wet conditions. Being able to brake down just those few feet later is all the difference in a race of closely matched cars.

If you can't run an ext. valve, you need more like 1.63" front dia 4 pistons to balance rear Z32s, and to run a Z32 rear prop valve to further reduce rear bias. It's still a tad front biased though, but going down to 1.38" front pistons and rear Z32s *might* work with the Z32 MC, but I think it'll then shift too much rear biased, especially with your smaller front rotor diameter. The ideal bias is somewhere around a 1.45-1.50" diameter equivalent front 4 piston on 12.2" rotors, so with your smaller rotors it'll shift more towards the 1.63" side, but I still think you'll be front biased without running the calcs.

It makes it way easier to shim the prop valve to give full rear line pressure then run a prop valve inside and it takes no time to really tweak it in, then back off like 1/4-1/2 turn in the wet.

Either way, it's a 11.67" dia rotor and the Z32 caliper is pretty compact being aluminum/top load design. Should easily fit under 15" unless there's something odd about your wheels. You'll just need to redrill the rotors for 4x114.3, which isn't a big deal. Spoke clearance shouldn't be a problem in the rear.



Somewhat crazy idea if you want to tinker some more on your brakes - you could probably put together a 4x114.3 mm off the shelf Wilwood hat + 11.75" x 0.81" rotor and get it to work with a Z32 rear caliper (that might need a little shimming to get happy with rotor placement on off the shelf hat). The rotor is about 2.2 mm thicker than a stock Z32 rotor, but taking off backing plates on pads, and maybe having to do some light grinding or starting off on worn pads would make it work. Maybe you could even get the Z32 caliper pistons faced down a bit by a local machine shop if they end up protruding a bit. You could end up with rear rotors that are a hair lighter than a stock S13 setup, but much bigger/more heat dissipation, and a cheap caliper (I'm not sure what Z32 rear calipers go for, but I know I got a set for like $50 back in the day as everybody wanted fronts more than rears). When comparing having to re-drill off the shelf steel rotors, vs. a little setup work and having to slightly grind down pads to work - I'd honestly think the Wilwood setup might be about the same hassle. Less unsprung weight is also a huge benefit.

If it were me, I think I'd make the Wilwood setup work. If you work out what Wilwood p/n you want, hit me up and I can probably save you a few bucks.

[Def]

Actually, it looks like an STi caliper of the early-mid 2000's vintage will bolt right up and has a 20 mm wide rotor stock which gets you closer to the 0.81", so stock pads might fit as is there?

https://www.zilvia.net/f/showpost.php?p=1342840&postcount=237

Rotor diameters are all really close, 11.75" falling in between Z32 and STi rear rotor size. Worth a look

[drbmw2002]

Def,

Thanks again for all the food for thought. This is the perfect time of year for that stuff, plus not sure what my plans are for the season so it might be another year without being able to get the car back on the track (covid has destroyed my "normal"). So I just wanted to back track for a little. I am running a tilton dual master cylinder set up (I tried to get the sizes but it's a pain to read on my back). I do have a brake bias adjuster that is accessible while driving. It's funny that you brought up the idea of making an aluminum hat with two piece rotor, just trying to get the weight down. I like the idea of STi caliper, I am assuming they are referring to the two pot caliper that the rally cars run. Then I went to price it and it was a little more pricey than I thought (about $100-$200) more for the calipers. I will keep looking. I know the z32 is the common upgrade and I located a set of calipers that is fairly priced. Like I said I am already incurring a weight penalty by switching the fronts might as well see what we can do in the rear.

Dan

[cdlong]

Just thought I would post something to pick everyone's mind. I currently race an s13 with SCCA in E Production. They finally changed the brake rules and allowed us, at a weight penalty, to upgrade from stock brakes. My biggest problem with the brakes was I was going through the pads at a pretty good clip......thank heavens for Carbotech's contingency. I know Def sells a front kit and I was hoping for the easy button. Of course the brake rules changed but the wheel size did not, 15x7 (I remember when 15x7 seemed like such a big wheel, haha). So none of the "big brake kits" would work. So after talking to Wilwood, they laughed at all the SCCA Production drivers calling them the past two months, I decided to go with a Dynalite and 11 inch rotor, same combo they already make for the MIatas. Anyway had to make my own hat and then a brake caliper bracket. At any rate, my question for people who have played with these longer than I have what did you all do for the rears, if anything? Right now after talking to Wilwood I am tempted to leave everything the way it is, just use the "bigger brakes" up front and leave the rears stock. However, since I have to take the weight penalty I was just curious to see if there are any other alternatives out there. Thanks in advance.

Dan

Can you provide some more info on that front setup? Are the brackets available somewhere or just conceptual at the moment? I'm interested in the same thing, though for autocross weight savings. I don't need big brakes for anything, and don't want to go back to stock (have z32 all around right now)

[drbmw2002]

So here is where things stand. In terms of the bracket I am picking it tomorrow, it was just something I made on my own and then took to a friend so he could make me an aluminum pretty one. As soon as it's finished I will let you know and then I am going to make a few, it's too easy not to. For the rear I went with the z32 caliper and just ordered a custom rotor from Coleman. Then back to the my friend and we are going to make the aluminum hats for the front and an aluminum hat for the rear Coleman rotor. This is just one of those projects I want to do once and not worry about again. Luckily I am in no hurry, I am a high school football coach, and they moved our fall season until the spring.........so there goes my racing season. CD once I verify the fit etc I will let you know about the brackets.

[Def]

Nice - that should be a great solution. Let me know if you need brake pads, I can give you a hookup on Hawk or Stoptechs. I honestly think Stoptech 309 Sports might work a treat in the rear with a vented rotor to keep MOT below 1300 F. They're so cheap you can buy 3 sets and always have spares!

The rear rotors don't do a ton on our cars, so you should get many many years out of each set of Coleman rotors. Not a bad solution.

[drbmw2002]

Def,
Thanks I stressed over this. Is it worth it, etc etc etc. I figured I had gone through the pains of doing the front might as well do all I can now and address the rear. Should never need to "upgrade" the brakes now. Spent the entire fall/winter replacing all the rod ends in the suspension, sent Konis out to be dyno tested and rebuilt/replaced if necessary, upgraded the brakes, replaced my old stand alone with a new MS and now onto the motor (I hate waiting for machine work but he is the best around so I have no choice.) Feels good to finally be putting stuff back together.

[cdlong]

So here is where things stand. In terms of the bracket I am picking it tomorrow, it was just something I made on my own and then took to a friend so he could make me an aluminum pretty one. As soon as it's finished I will let you know and then I am going to make a few, it's too easy not to. For the rear I went with the z32 caliper and just ordered a custom rotor from Coleman. Then back to the my friend and we are going to make the aluminum hats for the front and an aluminum hat for the rear Coleman rotor. This is just one of those projects I want to do once and not worry about again. Luckily I am in no hurry, I am a high school football coach, and they moved our fall season until the spring.........so there goes my racing season. CD once I verify the fit etc I will let you know about the brackets.

Thanks. Keep me in the loop if you can please. Got any details on the front caliper or rotor specs? I can't go SMALLER than stock, though that shouldn't be hard.