Brake MS sizing vs pressure question

**jonra23** · 08-09-2006, 01:48 PM

Nice spreadsheet Mick.

I take it that you enter the data in the yellow cells and calculates the other coloured cells.

Am in the process of putting one together that also takes in some of the variables that Oldcorallas has listed to also calc pedal travel, front/rear bias required etc.

regards
jon

**kingmick** · 08-09-2006, 02:10 PM

not my work ! i found it this morning when i was looking for stuff to show someone as i dont have any data here its all in sydney.

**kingmick** · 08-09-2006, 02:15 PM

there is good stuff there, but there would only be a handfull on here that would really get into it and use any of the fomula etc, thats why i stay away from posting anything like this.
Its not really relevent to most people that modify street cars or weekend track cars.

**oldcorollas** · 08-09-2006, 10:45 PM

if it is not your car, why post it? for all you know, it could be wrong.

i'd like to see data for YOUR race car, and see how close we can estimate the sizes..

however, i think many people would be bothered to calculate things... not just 1%. and i fail to understand your justification that it's not worth it for a street car or weekend track car...

anyway, back to the car at hand.

pedal force is 62lbs (car is american yeah?) and leverage ratio is 2.714
so force at B is 168.26lbs

bias bar width = 2.4", offset is toward the rear with 0.167" (i assume that means the balance bar pivot is now toward the rear MC, since no explanation is provided)
so, front to pivot is 1.367", and pivot to rear is 1.033

so front pressure amount is 1.033/2.4 = 43.04% , and rear pressure amount is 1.367/2.4 = 56.96%

so front = 72.41lbs, rear = 95.84lbs

front MC area = 0.4394 sq" so pressure in front line is 72.41/0.4934 = 164.78 psi
front MC area = 0.6013 sq" so pressure in front line is 95.84/0.6013 = 159.39psi
(different due to rounding errors, cbf)

and so on, but that is of little use, just replicating someones elses numbers that were found on a webpage...
and it's particularly unuseful talking about a car that weighs 290kg (is that with driver) which will have less weight transfer due to it's very low CoG, even compared to your old workshops sports sedan

however, it shows how simple it is to calculate. from tyre friction, to contact patch force, to brake torque, to disk diameter, to pad friction, to pad force, to caliper piston force, to fluid pressure, to master cylinder pressure and finally, if you have one, to balance bar split.
the size of master and balance bar split will be affected by the piston retraction and knockback also....
from there, modify for different weight transfer conditions, which increase or decrease any given wheels potential braking force... and there ya go

**kingmick** · 08-09-2006, 11:22 PM

lol i already said in a post a few back cant get my stauff till end if the month when im down in sydney!

So data is better than no data.

Jesus if someone always posted there own stuff there would be very little on the web for you guys to read up on and learn