Info Needed for Brake Bias Calculations

[WineCountryE30]

Hello everyone!

I am doing some calculations to determine the brake bias of several different possible setups for my E30. However I can not find the Brake Pad Widths anywhere. Does anyone know the numbers or know where I can find the information? Maybe I can get the parts store guys to pull the parts for me to measure... I also can't seem to find the sizes of the pistons from the E38 brembo calipers if anyone knows that off hand.

[ryan_george]

I find that RockAuto.com usually has drawings with dimensions of the parts. Should at least provide enough info to ball-park your calculations.

[AndrewBird]

Wow, someone actually calculating things instead of just throwing parts together. I'm impressed. Please share your findings once you have all the info gathered!

[WineCountryE30]

Thanks for the lead Ryan_George. - But I wasn't able to find pad thickness anywhere online except for some Hawk Pads info for the various calipers. I doubt its the exact stock numbers, but the variations between models should be close enough to stock for my purposes.

AndrewBird - Yeah I just don't see the point of spending a lot of my money to upgrade to an unbalanced setup that will take longer to stop no mater how "grabby" the front brakes feel. As for my data here you go buddy:

First the Disclaimer: Any or all of this could be wrong. Its based on a lot of 2nd hand data.

Next comes Credit: I am basing my calculations off of this excruciatingly detailed thread: http://www.m3forum.net/m3forum/showthread.php?t=412927 (He figured out info for his E46)

Now comes the explanation of what the main variables are:



Leg Force is simply how hard you step on the pedal. This seems standard from my research.

The stock Pedal Leverage is 4:1 on the E30. If you changed your brake pedal or linkage configuration you would need to change this.



Brake Pad choice makes a HUGE difference! Here are the values for the different pad options. I went with the Performance level pads for my calculations.



Here are the rotor, caliper, pad, and master cylinder sizes. If you change the variables in this table the results change below.



And finally here are my results. It displays the data for both an E30 MC and also the MC out of an E32.

I currently have E46 330i Front calipers and am putting a Z3M rear suspension with the E36 M3/Z3M calipers onto the car. But after looking at my chart I see that I will get closer to stock brake bias and more back wheel torque by making a bracket for a set of E46 330i Rear Calipers.


Drop Box link for the spreadsheet if anyone want to play with it: https://www.dropbox.com/s/2bb1hjp79j...ress.xlsx?dl=0

[ColonelMustard]

I think the formula for your piston area is incorrect.

You have 2*pi*diameter of piston. This gives you twice the circumference, not the area. If I correct these equations what I get is: 1.71 Bias; .63 Front and .37 Rear for the stock E30 set-up (line 26)

The link you posted also has incorrect formulas written too. (Equations 6 - 9 have an extra 2 multiplier out front.) However, his incorrect equations give you a correct final answer because you are getting a ratio of front to back brake torque.

[ColonelMustard]