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Looking to pick up/build off of 87FCTurboII's Thread from several years ago. I had originally found a brake bias calculator that I thought looked comprehensive enough. But, I ended up wanting to change more parameters, so I exported the script into excel in order to modify values that were set as static defaults.
So as of right now, I'm just looking for a gut check that everything in the file makes sense and to see if there is anything wrong. I'm also more than open for modification/additions, but don't want to go too far down the rabbit hole with it. Also, this file is set up based on pedal 'Leg' input and not Long Deceleration like the previous thread.
My initial check for a stock caliper with Hawk HPS as a substitute for OE, came up with a ratio of F:68% vs. R:32%, which is close to 87FC's calc, but I believe we did use different bad Cf.
Great work here, Brian! I too sought to expand on the work done by others, and pursued building a calculator of my own. I was having big problems at the track with locking up the front tires, and I knew I could improve my lap times significantly if I could reduce this.
Attached is my own spreadsheet; it has gone through many iterations, and I'm happy with where it's at, but I won't say it is 100% complete. I've done my best with the calculations and used many resources online to pull various parts into a single calculator. The calcs in your spreadsheet do look the same as mine, and I've used the same calculators on TCE's website that you reference in your file. I did expand the calcs to show bias as a function of deceleration (the same way 87FCTurboII did). Also, I included proportioning valve inputs so that you can calculate bias with the stock ABS system or with an aftermarket proportioning valve.
Full disclosure: the Wilwood proportioning valve data (and much of my inspiration) came from Wilhelm Raceworks: https://wilhelmraceworks.com/brake-bias
-Justin
I would be very interested in looking at a calculator. I have tried to do some research but I got lost in the numbers really quickly.
Would it be possible to add a specific caliper to that calculator? Got a pair for massive units that I want to use but I'm curious which way I should go with the rears. I've heard it's easily overpowered in the rear.
No problem at all to add a specific caliper to the calculator, which one did you have in mind? Also, which caliper are you using on the front?
In my experience, it isn't difficult to over power the front OR rear bias. I designed my brake system such that I can use the exact same pads on the front and rear of the car, relying on rotor size, piston area, and the proportioning valve to get the bias where I want it.
Based on my calculations, I don't think that Maserati caliper is a good idea for the FD. At 5,500 mm2 of piston area, it is simply way too large. To bring the bias within a reasonable range of the stock FD, you would need a rear piston area of about 2,600 mm2, along with a rotor at about 330 mm.
Also, even with a very large rear caliper, the front torque produced at the front of the car is so high that the rear line pressure does not actually reach the "knee" of the factory proportioning valve (inside the ABS system). This means the bias is a flat line as a function of deceleration, mitigating the benefits of the proportioning valve.
See attached for the calculation. I made many assumptions, so feel free to change the values to fit your car.
p.s. A larger master cylinder is almost certainly going to be a good idea if you're talking about increasing the piston sizes.
It's for my FC, not FD. Hence the "FD rear disc upgrade". Also, no ABS.
The rear calipers that I was considering have a total area of 2770mm2 per caliper. But I need a parkingbrake caliper with that and couldn't find affordable ones that are usable.
OEM rear caliper is 908mm2; 273mm and 3210mm2 pad area.
Don't know pad area on both maserati brembo calipers
Well, with rear calipers that large, technically, the bias could be brought into a workable range. A couple of thoughts:
The stock FD rear rotors are a bit small for this design; you could compensate by using a much lower coefficient pad in the rear, but I think the better design is to use a larger rotor (especially if you intend to track the car)
The lack of ABS is what really makes this feasible, but you would absolutely need a proportioning valve (connected to the rear brakes)
I would still have concerns about fitment; I imagine calipers that support that much piston area have to be quite large, and coupled with quite large rotors, it likely won't be easy to fit wheels around them.
My other concern is brake pedal feel and the master cylinder. I have significantly smaller piston area in my car (2,600 mm2 in the front, 1,271 mm2 in the rear), and my 1" master cylinder still isn't enough for my liking (using the stock FD booster). I imagine using calipers as large as what you're talking about would result in a soft brake pedal feel. Of course, this is subjective; I prefer a more firm pedal with less travel.
New version attached. There are several variables that are just guesses, so feel free to add more data.
I had a set of wheels that could fit these calipers. Unfortunately someone bought them so I need to order a new set
I could go even bigger then FD rear discs. But the thing I'm hearing left and right is that rears on an fc are easily overpowered. So I was hoping FD size would be sufficient. And hoping I could get away stock rear caliper for some time and do a caliper swap later.
The original proportioning valve is also still installed. I'm not sure how I feel about regulators but I might misunderstand those because I've never looked at proper ones and don't know if they are different from just being a valve that is being closed.
