Yeap agreed! From jakelatham: Axle Torque = 2 (Discs) * (Piston Area) * (Line Pressure) * (Effective Radius) * (Pad Coefficient) * 2 Piston Area being just one side of the caliper.
Still re-reading latest posts and getting my own head round it all, but on this; I am drawing comparisons on master cylinder to piston tratio to depict pedal travel as it chamges with differing setups rather than measuring actual physical travel under foot. Appreciate this is all subjective to my own experience of pedal travel using the OEM setup and then how it will get longer or shorter, I personally am erring towards the Ksport setup for example which in theory will work with a shorter pedal travel, OEM ratio being 12.05 and Ksport reduced to 10.2, 15% shorter pedal with the later setup. While its in my head another theory drawn from the data is that although the larger master cylinder produces less pressure for the same foot pressure, because of larger piston area at the caliper a similar force is applied to the pad as the OEM but with a larger pad area benefit. EDIT: Hope the theory of the last paragrpah is right, data supporting these particular setups to be wrong, see knew data in post below.
thank you daved I've decided that the 9" servo gives across the board additional 100.9% pressure to any given manual pressure and adjusted the table accordingly. I've just hand cranked these revised calculations, apologies if there are typo or mis-calcs, is the "free pressure" of 100.9% additional for a 9" servo correct? Master cylinder Caliper Total caliper piston area square inch Master Cylinder area square inch Foot Pressure lbs Pedal Ratio Servo Assist psi Pressure applied psi M/C ratio to piston Pad Pressure lbs 22mm OEM 54mm 7.096 0.589 70.4 5 603 1201 12.05 8523 25.4mm OEM 54mm 7.096 0.785 70.4 5 452 900 9.04 6386 22mm Wilwood 4pot 38.1mm 7.065 0.589 70.4 5 603 1201 12 8485 25.4mm Wilwood 4pot 38.1mm 7.065 0.785 70.4 5 452 900 9 6358 22mm Wilwood 4pot 44.5mm 9.638 0.589 70.4 5 603 1201 16.37 11575 25.4mm Wilwood 4pot 44.5mm 9.638 0.785 70.4 5 452 900 12.28 8674 25.4mm AP6600 4pot 37.3/41mm 7.476 0.785 70.4 5 452 900 9.52 6728 25.4mm Ksport 6pot 36/36/26mm 8.004 0.785 70.4 5 452 900 10.2 7204
Strimmer, Great work and thanks to all contributors Perhaps the above could be expressed as follows, figures approximate and ignoring mechanical friction issues etc: Since the replacement 25.4 mmd master cylinder is 15.5% larger than the 22.0 mmd original - - Duplicating the original caliper piston/s pressure (not pad pressure as it varies with pad surface area) requires increasing the original caliper piston/s area by the same 15.5%, being 7.096 sq in. x 15.5% = 8.196 sq" The closest match from your table is the K Sport 6 pot 36/36/26 caliper at 8.004 sq" We have now engineered a system in which the same pedal travel forces a 15.5% greater volume of brake fluid through the brake lines and requires a little less pedal travel before the pads contact the discs, where they apply a little less pressure than the oe system, resulting in marginally inferior braking performance - - If retaining the 25.4 mmd m/c, the increased caliper piston/s pressure desired for superior braking performance will require either the Wilwood 4 pot 44.5 mmd 9.638 sq" calipers from the list, and/or increasing the pedal leverage ratio, and/or increasing the servo diameter The latter alone will retain oe pedal travel whereas the former choices will increase it Incidentally, ignoring issues such as improved heat dissipation, increasing the pad surface area alone of any combination will improve pad/disc durability but not braking performance per se
After another re-read I am both massively impressed with the contributions from all and largely embarrassed at how much I missed as I was only scanning thru umpteen previous times. I missed this post from previous reads, sums up exactly what I want to achieve. Grateful for LeftcoastTigger putting figures into words. Discovered from a quick forum search a 23mm m/c exists and offered it into the Ksport system to address the lower pressure issue. Master cylinder|Caliper|Total caliper piston area square inch|Master Cylinder area square inch|Foot Pressure lbs|Pedal Ratio|Servo Assist psi|Pressure applied psi|M/C ratio to piston|Pad Pressure lbs 22mm|OEM 54mm|7.096|0.589|70.4|5|603|1201|12.05|8523 22mm|Wilwood 4pot 38.1mm|7.065|0.589|70.4|5|603|1201|12.00|8485 25.4mm|Wilwood 4pot 44.5mm|9.638|0.785|70.4|5|452|900|12.28|8674 23mm|Ksport 6pot 36/36/26mm|8.004|0.644|70.4|5|551|1098|12.43|8789 Perhaps time I look into the changing effect at the pad and disc now.
This has made a very interesting read thanks guys. I've gone from standard 280mm calipers on my Corrado VR, to TT 312mm discs/calipers and now run Boxster rears on the same 312mm discs, so have a basic understanding of the differences these changes make. The feel I get from the pedal is very good but there is not enough ultimate power, as shown in one of the tables, very comparable to the sliding caliper I had before, infact. The straightforward option is to move to 323mm discs and Cupra R Brembo calipers for extra power, but at the expense of pedal travel and initial feel. You've given me some food for thought, thats for sure.
Likewise, I'm going to need to give this thread a total re-read again! Dropped off the pace a page or so back, but I know I'm coming back to it!
