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I've been on a BBK kick lately, and finally had the urge to explore all of the DIY (meaning not off the shelf complete kits) options available. The 996 Brembo path is the most known, and despite it being common knowledge that it messes with the brake bias, a lot of the info was hearsay. With that said, I think the 996 Brembo option is just dated. By this point there has to be other easy to get front Brembo calipers that are better suited to go along with the 996 rears. The following are the calculations I came up with for various DIY options to see how they relate to the factory e36 M3 brake bias.
**Take note, that these bias %'s are not meant to be real world accurate, but instead a comparison to the calculated factory bias as certain variables are changed (rotor size and caliper piston size). In other words, the goal is to see how and to what extent certain rotor and caliper changes deviate from the calculated factory number.
This is the calculator used:
https://brakepower.com/brake-bias-static.htm
The only variables changed are the 4 values relating to caliper piston area and rotor effective radius. The factory e36 m3 MC front and rear bore is used (25.4/20.64), the CoF of brake pads are kept constant. The "Static Brake Bias" is the final brake bias value output that is being observed.
A note about "Effective Radius of Brake Rotors," which can cause some confusion:
"The effective radius of a brake rotor is measured from center of brake pad to center of brake rotor. In other words, it is the distance from rotor-center to halfway the swept area of the rotor.
More accurately but less easy to measure: it's the distance from rotor-center-line to center line of caliper piston(s)."
On the the numbers...
Factory E36 M3
Front - 315mm (eff rotor radius -31.75mm), 125.8mm (eff rotor radius), 60mm piston, 2827mm2 piston area
Rear - 312mm (eff rotor radius -21.72mm), 134.3mm (eff rotor radius), 40mm piston, 1256mm2 piston area
Brake bias 65.6% front
996 Brembo
Front - 345mm (eff rotor radius -90mm x .66 /2= -29.7mm), 142.8mm (eff rotor radius), 2273mm2 piston area
Rear - 328mm (eff rotor radius -73.16mm x .75 /2= -27.4mm), 136.6mm (eff rotor radius), 28 30mm piston sizes, 1322mm2 piston area
Brake bias 61.9% front - 5.6% reduction in front bias
w/ 325mm front rotor, 132.8mm (eff rotor radius) - Brake bias 60.2% front - 8.2% reduction in front bias
Megane RS275 Brembo Front / 996 Rear https://freakyparts.co.uk/collection...rake-kit-front
Front - 345mm (eff rotor radius ~-70mm /2= -35mm), 137.5mm (eff rotor radius), 40 40mm piston sizes, 2513mm2 piston area
Brake bias 63.4% front - 3.4% reduction in front bias
w/ 360mm (e9X M3) front rotor, 145mm (eff rotor radius) - Brake bias 64.6% front - 1.5% reduction in from bias (Freaky Parts custom front kit)
DB9 Brembo Front / 996 Rear (brackets need to be custom)
Front - 345mm (eff rotor radius ~-72mm /2= -36mm), 136.5mm (eff rotor radius), 44 40mm piston sizes, 2777mm2 piston area
Brake bias 65.5% front - NO reduction in front bias
AP CP8350-24S4 Front / Stock Rear (brackets need to be custom)
Front - 332mm (eff rotor radius -42mm /2= -21mm), 145mm (eff rotor radius), 38.1 / 41.3mm piston sizes, 2480mm2 piston area
Brake bias 65.9% front - 0.5% increase in front bias
CLK/SLK(05-09) BMB-64 6 pot front / 996 Rear (brackets need to be custom)
Front - 360mm (eff rotor radius -90mm /2= -45mm), 135mm (eff rotor radius), 30 34 38mm piston sizes, 2749mm2 piston area
Brake bias 65.0% front - 0.9% decrease in front bias
E55 AMG W211,etc. (03-06) BMB-81 8 pot front / 996 Rear (brackets need to be custom)
Front - 360mm (eff rotor radius -95mm /2= -47.5mm), 132.5mm (eff rotor radius), 28/32 28/32mm piston sizes, 2840mm2 piston area
Brake bias 65.4% front - 0.3% decrease in front bias
ECS 345mm front rotor kit
140.8mm (eff rotor radius) - Brake bias 68.1% front - 3.8% increase in front brake bias
w/ 42mm piston size + 328mm rotor - Brake bias 64.7% front (if ECS offered brackets to run the e46 M3 calipers and rotors)
Just the %'s...
Factory E36 M3 - 65.6% front
996 Brembo F/R 345mm rotor - 61.9% front - 5.6% reduction in front bias
996 Brembo F/R 325mm rotor - 60.2% front - 8.2% reduction in front bias
Megane RS275 Brembo Front / 996 Rear 345mm rotor - 63.4% front - 3.4% reduction in from bias
Megane RS275 Brembo Front / 996 Rear 360mm rotor - 64.6% front - 1.5% reduction in from bias
DB9 Brembo Front / 996 Rear 345mm rotor - 65.5% front - NO reduction in front bias
AP CP8350-24S4 Front / Stock Rear 332mm rotor - 65.9% front - 0.5% increase in front bias
CLK/SLK(05-09) BMB-64 6 pot front / 996 Rear 360mm rotor - 65.0% front - 0.9% decrease in front bias
E55 AMG W211,etc. (03-06) BMB-81 8 pot front / 996 Rear 360mm rotor - 65.4% front - 0.3% decrease in front bias
ECS 345mm front rotor kit - 68.1% front - 3.8% increase in front brake bias
ECS 345mm front rotor kit w/ hypothetical E46 M3 rear - 64.7% front
Something to keep in mind, which I have not shown here, is that a certain % reduction in the front bias results in a much larger % increase in rear bias. Take for example the 996 Brembo F/R 325mm rotor - 60.2% front - 8.2% reduction in front bias. If the distribution is 60.2F/39.8R, an 8.2% reduction in front bias results in a 15.7% increase in rear bias.
Please by all means, double check my numbers and play with the calculator. But based on the deltas I am seeing here, the Freaky Parts front option is pretty solid. Especially if you are running 18" wheels, that 360mm front rotor possibility is pretty awesome.
Also, if anyone definitively knows caliper piston sizes of various stoptech, brembo, etc. complete kits post them up and I’ll add it to the original post to compare.
Last edited by bimma360; 06-16-2023 at 02:35 PM. Reason: to incorporate MC bore sizes into calculations
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I wouldn't focus too much on the percentage increase or decrease, focus on the f/r bias percentages. (Percentage increase of a percentage is always a little odd.)Originally Posted by bimma360
Even for a street car, on the E36 chassis moving bias forward a bit (compared to stock) is fine, especially if you're running a summer tire. I would not move the bias further back compared to stock.
Someone makes E36 brackets for the 135i brembo calipers (no idea what the bias is).
FYI, none of these are *needed* for a street car, or for most track cars. All Spec E36 & Spec E46 race cars use the stock calipers and rotors.
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I hear ya. % reduction and increase is just there for reference. I think at this point, it goes without saying that non of this needed for a street car. There are a lot of things we do to our cars, that aren't needed to be honest. Ya know? I THINK moving the bias to the rear a small amount is ok. I, however, am not convinced moving it back to the extent the 996 F/R setup is ok. For my comfort, I think the items marked in green are acceptable. Probably even the one in yellow.
Edit: Btw you quoted me while I was updating the first post hahah.
Last edited by bimma360; 05-29-2023 at 04:29 PM.
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I think there is a fairly adequate amount of info out there regarding the 996 calipers as being a less-than-optimal braking upgrade. The only kits I have heard folks rave about are either Brembos or AP Racing. Then the PFC direct drive rotors and better pads as the cost-effective option. Lee / Massivebrakes also has some good solutions using Wilwood calipers, but likely require running bigger wheels.
I need to do some more trial-and-error troubleshooting on my brake system, as I really hate how there is no linearity to the pedal travel. The first half of travel for me is soft, it then crosses a threshold and firms up significantly. I would really like to have a firm pedal feel with an inch or two of travel, as it's what I'm accustomed to on my other cars. After reading in the track forums it seems like I may have some pad taper issues to figure out.
Thanks for putting this info together.
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There are many Wilwood solutions that fit 17" rims, and are a quality solution. They even make some of the calipers with dust seals.
AP stuff is a notch above, but are a poor choice for a road car (no dust seals and knock back springs are a terrible street choice).
The 996 calipers are a mild upgrade vs OEM, but correct, they don't increase braking capacity (none of the solutions that keep the OEM rotor do).
Your pedal travel can not be made to feel like a modern sports car without major re-engineering of the brake system. The big culprits are the M/C and booster design. Pads with high initial torque might help, but the pedal will still travel an inch or more before the system builds pressure.
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I think StopTech is a good option too.
Last edited by sfcarguy; 05-30-2023 at 05:54 PM.
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Well sure, Stoptech, PFC, Brembo, Wilwood, and others all make quality BBK setups for either front, rear, or both. I think the point of this thread though was to discuss other "DIY" options which don't involve buying off the shelf BBK kits.
As has been said though, the benefits on an E36 are mostly cosmetic. Stock size rotors/calipers with more aggressive cooling and obviously pads seem to be the best price/performance option in the track/race world. Especially if your car has been lightened at all.
1999 M3/2/5 - Titanium Silver - Track/Weekend Toy
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I took Stoptech out of my consideration set after Centic was purchased by First Brands Group. Lots of horror stories regarding their QA once they moved everything offshore.
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Yeah let’s keep the convo to DIY options. We all know off the shelf options exists, and that the factory brakes are fine. If anyone does have piston sizes for off the shelf kits, however, I’d be more than happy to throw them in the calculator and added to the thread for comparison’s sake.
If we want to talk about stock brakes though, I will say that the ECS 345mm rotor kit would a fantastic stock type upgrade IF they offered a bracket to run e46 m3 rear calipers and 328mm rotor. Turner does suggest to just run more aggressive pads in the rear to compensate for the brake bias, but I’d prefer a rear kit instead haha.
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Too bad I cannot fit the giant(compared to my stock 98 equipment) Brembo calipers and rotors from a 2018 M2. I have those just sitting around with all the other stock parts that were stripped to make it a dedicated track car.
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What if you bought 18” wheels?
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Are those the 4 piston fronts 2 piston rear ones?
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I need to check the back but the fronts are the 4 piston.
- - - Updated - - -
That might actually work. I would have to take measurements. But worth looking into.
📷: @nholmes74
LARGE IMAGE WARNING
Am I the only one running Brembo "big reds" (yes mine are painted black) up front and 996 rears?
It's a super goofy set-up that originally came as a Mov'It kit from Europe. This has their front top hats and a machined rear aluminum top hat. I order rotors from Coleman racing and they're about $200 a corner. I'm also 99% sure the brake bias is crazy wonky right now, too. The rear pads last almost 3x as long as the fronts. I go through front rotors and pads about once a year. Ignore the slotting, I don't use slotted rotors anymore. I also forgot to mention this set-up fits under OEM 17" wheels and all aftermarket wheels.
Front rotors are 320mm x 24mm
Rear rotors are 302mm x 24mm
Porsche Big Red Piston Sizes
44mm
36mm
Big red four piston versus 996 four piston:
Fronts w/ radial mount
Rears
I had to remove the e-brakes to make this kit work:
Last edited by golgo13; 06-02-2023 at 12:40 PM.
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Those are some big calipers!
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I think the 4 piston fronts are axial mount calipers which makes things a bit more difficult with mounting.
Do you know what the piston sizes are on those big reds? I’ll throw them into the calculator and see where your set up is at. Where do “big reds” come from?LARGE IMAGE WARNING
Am I the only one running Brembo "big reds" (yes mine are painted black) up front and 996 rears?
📷: @nholmes74
There are two piston sizes:
44mm
36mm
The big reds were offered on a few different models based on my poking around online, but more specifically Porsche 911 (993) Turbo (1996-1997)
Last edited by golgo13; 06-02-2023 at 12:37 PM.
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I find this really interesting that it only uses piston size and doesn't look at pad size / area.
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Pad area doesn't matter (won't change torque at a given clamping pressure), except for heat capacity.
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Very interesting thread. I used the six piston calipers from the 1M I believe. ECS sells the kit. Although the kit comes with 325 rotors, I had a custom bracket made to use two-piece 345s.
On the rear I use stock caliper, rotor and bracket from the E46 330i. There are 315.
Hawk ht10 pads all around. Somehow it seems to be very well balanced between front and rear. And very stable from slightly warmed up, up to full temperature after 45 minutes session on track. So much that my last driving instructor wanted to know exactly what breaks I was using. He was really amazed at how well they worked.
Sent from my 2201117TG using Tapatalk
Last edited by Greenday694; 06-02-2023 at 04:50 PM.
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"Big Red" (993 Turbo) Brembo Front / 996 Rear
Front - 320mm (eff rotor radius ~-75mm /2= -37.5mm), 122.5mm (eff rotor radius), 44 36mm piston sizes, 2537mm2 piston area
Rear - 302mm (eff rotor radius -73.16mm x .75 /2= -27.4mm), 123.6mm (eff rotor radius), 28 30mm piston sizes, 1322mm2 piston area
Brake bias 63.3% front
w/ 345mm front rotor, 135mm (eff rotor radius), - Brake bias 65.5% front
So it looks like the Big Red calipers actually have just about the same piston area as the Megan RS275 Brembo's. So the bias numbers, with your front and rear rotors, is identical to the 345/328 Megane/996 set up. On paper the bias isn't that bad. Can you describe what you mean by it being wonky? Something to consider. HOWEVER, it does look like with a 345mm front rotor and keeping your 302mm rear will get you right back to the factory bias.
Factory E36 M3 - 65.6% front
Megane RS275 Brembo Front / 996 Rear 345mm rotor - 63.4% front - 3.4% reduction in from bias
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So here is something cool. By swapping the MC from the e36 M3 (25.4F/20.64R) to the e46 M3 (25F/22R) with the 345mm front rotor you get right back to the factory e36 M3 brake bias on the 996 Brembo F/R kit. And it's not that bad with the 325mm rotor either. One thing to note is that I could only find the e46 m3 MC values to be 25/22. If there is a more precise number, and someone knows it let me know and I'll update these numbers. Now I don't know if this MC swap is possible to do, or what it means for pedal feel and travel. But it does compensate for the rear bias in the full 996 setup. The final numbers below.
Factory E36 M3 - 65.6% front
996 Brembo F/R 345mm rotor w/ E46 M3 MC (25/22) - 65.6% front - 0% reduction in front bias
996 Brembo F/R 325mm rotor w/ E46 M3 MC (25/22) - 64% front - 2.4% reduction in front bias
- - - Updated - - -
Pretty cool. When I have time I'll try to find the piston sizes of the calipers. But if you can do it in the meantime, just post it up and I'll run the calculations. Curious to see where it ends up.
📷: @nholmes74
Very neat! Thank you for taking the time to add my set-up to your calculations. I really appreciate it for sure.
I did fail to mention that I'm currently using the Z3 3.0i M/C which will certainly have different F/R bias. I went with that because my car has MK60 ABS.
Wonky in so far as it's an uncommon set-up, uses "custom rotors," has a machined rear top-hat, required me to remove the e-brake assembly and has an odd size for the rear rotors (302mm)
That's really interesting. I'm curious how adding a larger rotor would help since this current kit uses 100% of the pad sweep area over the surface of the rotor right now @ 320mm. What would adding another 25mm in rotor diameter gain? I guess it would help dissipate heat for sure.
Can you please help me understand the math in your calculus? I'm not a math guy so I'm confused.
Can you explain why my current set-up has a smaller overall piston area when both variables (rotors and pistons) are larger than the OEM set-up?
OEM E36 M3 calipers
Front - 315mm (eff rotor radius -31.75mm), 125.8mm (eff rotor radius), 60mm piston, 2827mm2 piston area
My current Big Red calipers
Front - 320mm (eff rotor radius ~-75mm /2= -37.5mm), 122.5mm (eff rotor radius), 44 36mm piston sizes, 2537mm2 piston area
Last edited by golgo13; 06-02-2023 at 06:16 PM.
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A larger rotor moves bias to the end it's installed on. It increases the radius that the clamping force is applied to, increasing the torque at the spindle.
Not quite sure what you're asking about piston area, but piston area is simply the area equation for a circle.
Area = Pi x radius^2. Same as, Area = Pi x radius x radius.
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Piston Area
Sure! On the piston area, during my research I found that a lot of people get confused on how to account for the stock sliding caliper. A single piston sliding caliper will act like a 2 piston caliper, therefore you count the surface area of the piston twice. Along those lines, in the calculations it doesn't matter if you use the total surface area of all pistons in a caliper or just a single side as long as you stay consistent. So here is how we get those numbers...
Stock E36 M3 - 60mm piston | pir2 | pi(30)2 = 2827mm2
"Big Red" Front - 44mm & 36mm pistons | pir2 + pir2 | pi(22)2 + pi(18)2= 2537mm2
And as you can see the big reds actually have a smaller piston area than the stock 60mm calipers.
Effective Rotor Radius
This is where it can get tricky, as the effective rotor radius is from the center point of the rotor to the midpoint of the brake pad. So if you have a 320mm rotor, the radius is 160mm, but the effective radius will be less once you figure out where that brake pad midpoint is. For that you need the brake pad measurements for any particular caliper. Something to note, is that since different calipers will have different pad sizes, the effective rotor radius can actually change depending on the caliper even if the rotor size remains consistent.
Ok so on the big reds, here is the front brake pad sizes I found online:
https://cdn.shopify.com/s/files/1/07...g?v=1678826580
This isn't 100% precise b/c of the shape, but the brake pad height is 75mm and the midpoint is midway so (75/2) 37.5mm. Making the assumption that the top of the pad material is at the top of the rotor, the effective radius of your rotor is 160mm - 37.5mm = 122.5mm. Turns out, that even though the factory rotor is 5mm smaller in diameter at 315mm, using the factory calipers/pads yields an effective rotor radius of 125.8mm.
So the effective rotor radius of the factory system is actually bigger than the big red set up with a 320mm rotor. Increasing the rotor size, will therefore increase the effective rotor radius and in turn move the bias further forward vs your current setup.
The way I wrapped my mind around all of this, is thinking all of this as a function of "braking power" (probably an incorrect use of terminology, but who cares). Increasing the piston area increases braking power. Increasing the rotor size, increases braking power. And obviously decreasing these decreases braking power. Brake bias is the just the ratio of braking power front vs rear. In your set up, vs stock, you both increase the piston area in the rear and decrease the effective rotor radius. In the front, you decrease the piston area and at best about keep the same rotor radius vs stock. So generally you are decreasing braking power in the front, and hard to tell what's going on in the rear. But if you put all of those in the calc, it turns out that you are shifting bias towards the rear.
That's all assuming a stock e36 M3 MC and ABS system. I honestly couldn't tell you or calculate what the MK60 ABS is doing to the overall bias, but the Z3 3.0i MC will certainly move the bias around vs the numbers we got in my previous post.
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