I've just finished modifying and fitting mine, I altered the pivot location and pedal to have the ratio of 6.2:1, the autocavan dimensions produced 5.4:1 pedal ratio. Now it's bled and feels pretty good. The travel of the pedal is around two inches, not solid as a rock, a little squishy, I've nothing to compare to so it feels like a standard car with a servo kinda squishy-ness! (and there could still be air in the system) I can't get megasquirt to work properly so the car doesn't run at the minute, so no testy testy. I also bought some ferodo ds3000 pads but would like to test the whole system with the old pads to see if i've made an improvement, then chuck them on.
Front = .625 Rear = .700 Handbrake = .700 Both are wilwood ones from rally design, along with the balance bar.
Come back to re-read thread I missed posted link to http://www.ducatimeccanica.com/brake_ratios.html where brake master cylinder to wheel (caliper) cylinder ratios of 27:1 to 23:1 recommended, has this been acknowledged as useable calculation, as I'd like to perform the following calculation and might buy calipers based on this. I have already because of previous choices fitted a 25.4mm Audi master cylinder to the standard 9" servo and visiting the Wilwood range thru Rallydesign found this Wilwood 4 pot calipers (Dynalite/Midilite or Superlite) 44.5mm pistons Total piston area across both calipers of 12436mm. Working on a m/c area of 506mm to the caliper piston area total of 12436. Master cylinder to caliper piston ratio of 24.5:1 Am I making sense?
From a quick glance at my maths:. Take a standard Mk1 Golf GTI: M/cyl dia M/cyl area Brake pot dia Brake pot area No of effective pots Overall ratio 20mm 314.16sq mm 48mm 3619sq/mm 11.52 This ignores pedal ratio obviously, which is also very key to this.
Lifted your table till I become proficient at them myself To compare my suggested option 1st in the table against the OEM 2nd M/cyl dia M/cyl area Brake pot dia Brake pot area No of effective pots Overall ratio 25.4mm 506.45sq/mm 44.5mm 6218sq/mm 4 12.28 22mm 379.94sq/mm 54mm 4578sq/mm 2 12.05 Suggesting that the feel/pedal travel should be about the same with the new setup as the OEM because the ratio is maintained and all other components in the system remain unchanged.
Strimmer, I've added (effective) pots to your table, single pot VW being effectively 2 due to the design. Looks good, though I didn't check any numbers! I guess the only thing is whether pedal force changes. In theory not, but it is multi dimensional this stuff, so worth a check on issues raised in the thread. Look forward to hearing the results
Working on another spreadsheet to take this out to another step of relative pressure applied across the pad surface but not sure if I'm right in thinking that if 1000psi is pressure applied at the caliper and the caliper has a total piston area of 7 square inches is 7000lbs being applied to the pad?
Pulled this data off a spreadsheet I have running highlights the effects of piston bore choice and master cylinder size. I found it intersting to create, helped me understand it all as I'm not greatly gifted with hands on knowledge. Might be of use. I pick and choose master cylinder and calipers to create a setup close to stock/current setup which may feel similar under foot and retain pedal travel. Just speculation at the moment. 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 5 595 1193 12.05 8464 25.4mm OEM 54mm 7.096 0.785 70.4 5 595 1043 9.04 7404 22mm Wilwood 4pot 38.1mm 7.065 0.589 70.4 5 595 1193 12 8427 25.4mm Wilwood 4pot 38.1mm 7.065 0.785 70.4 5 595 1043 9 7372 22mm Wilwood 4pot 44.5mm 9.638 0.589 70.4 5 595 1193 16.37 11495 25.4mm Wilwood 4pot 44.5mm 9.638 0.785 70.4 5 595 1043 12.28 10056 25.4mm AP6600 4pot 37.3/41mm 7.476 0.785 70.4 5 595 1043 9.52 7801 25.4mm Ksport 6pot 36/36/26mm 8.004 0.785 70.4 5 595 1043 10.2 8351
Interesting numbers. I would need to get my head back in the books to get a feel for the data. Gut feel is the increase at 22/44.5 is not equated with reality, despite the apparent pad pressure increase it suggests. Really awesome putting together that info though, and I'm sure I'll be back to this sooner or later. My Wilwoods need a refurb and it might end up with them being replaced. I'd almost be tempted to buy both sets and test them back to back to get some sense of it, then flog the set I don't need.
Strimmer. I get some with different numbers to you? Total Piston Areas in 1 Caliper: 54 Dia = 2290mm^2 x 1 = 2290mm^2 = 3.54"^2 38.1 Dia = 1140mm^2 x 4 = 4560mm^2 = 7.62"^2 44.5 Dia = 1555mm^2 x 4 = 6220mm^2 = 9.64"^2 37.3/41 Dia = 1092mm^2 x 2 + 1320mm^2 x 2 = 4825mm^2 = 7.49"^2 I can't get my head around the Ksport - 6pot 36/36/26/4mm I also found this which gives more servo assist data! Unlike a servo, an engine driven hydraulic pump gives constant assist even at high revs when the engine vaccum is minimal. A leaking hydraulic system is easily seen, whereas, a leak in the vacuum system is impossible to see. Although it adds more weight and robs the engine of 1/2 kW. From my own small experience of making poor braking systems work I give the following: Audi 50 (Polo Mk1): Awful as recieved, second hand from a VW Dealer's Mechanic, with VAG O.E. Discs and Pads. Awesome with ATE Power Discs and EBC Green Stuff Pads. Well awesome for a non-servoed Polo Mk1 or Golf Mk1 on an O.E. set up. 90Q 20V: Awful grunching crunching from O.E. Textar Pads on O.E. Discs. Even a change to Mintex 1144s did not help much. A switch to Brembo Group N (Soft) Cross-Drilled Discs and matching Brembo Pads, at both ends, and it stopped on a sixpence! From all engine speeds, as it has a hydraulic pumped system!
Just had a brief glance thru daved, typo error with the ksport, now edited the table with the erroneous "4" removed. I'll triple check the figures, not sure how you are converting square mm to square inches, I convert the piston bore from mm to inch then calculate total area but as I say will check it over again tonight and read over the servo assist information too.
Dave, the theory behind the calculations for the single pot caliper is you assume that it has double the working piston area due to it's sliding nature, distributing the force equally on both sides. This is how you get to the ~7" area for standard calipers. A little point this info would be much nice in Bar, N and mm's all round save all the unit conversions that are taking place. But if you like psi and lb's then stick with it.
Mike. Surely the total force available can only be: Line pressure x total piston area. For a sliding system, this force is just split in half? I wanted to say that, but I had not got the guts! And, being the unbearable pedant that I am: Foot Pressure and Pad Pressure should be Foot Force and Pad Force! Also: Pedal travel should be included, as a larger master cylinder needs less travel, for any given piston area to disc clearance ratio!
We need to come back to every action has an equal and opposite reaction to see how this works Dave. As caliper piston pushes against the disc this causes the equal and opposite reaction to push the sliding caliper the other side. Or another way of thinking about it is the caliper body is actually just another piston which can move once the first piston has been pressed solid against the disc. Having similar area for the pressure to work on as the original piston. Thus the effective area is double that of just the one piston. So therefore double the force. Also mentioned also be LeftCoastTiger in his posts earlier in the thread, with links to rally design where this method of calculating sliding calipers is also stated.
Just re-thought it. Split in half was stupid terminology! I did actually sort of know that for every action there is a reaction of equal magnitude, and I still maintain that the total force available can be no more than area x pressure. What has got me in a tiss at the moment is the effect of opposing pistons, As far as I can see, the second piston is there to act as a reactive support for the other piston, just like the sliding member in a single sided caliper. So the gripping force is just one piston area x pressure! Cos, if one piston had less force behind it it would move inwards due to the larger force on the second piston, and bend the disc until pressures, and hence forces, are equalised! I'll check out the earlier posts and see if it helps me see what I appear to be missing. I was off on the sick when a lot of the good bumf below was posted, and am trying to catch up! Flipping heck, back in the day I designed some blooming big disc brakes on machines. The ones on the 75 tonne ladle crane at BSC Port Talbot were 2m, or so, in diameter! Must admit, my brain is uber slow these days!
This is the one! http://www.jakelatham.com/radical/info/brake_calculators.shtml You do only take one side of the caliper as I have just realised below. So. Total Piston Areas in one side of Caliper: 54 Dia Four Pot = 2290mm^2 x 1 = 2290mm^2 = 3.54"^2 38.1 Dia Four Pot = 1140mm^2 x 2 = 2280mm^2 = 3.53"^2 44.5 Dia Four Pot = 1555mm^2 x 2 = 31100mm^2 = 4.82"^2 37.3/41 Dia Four Pot = 1092mm^2 x 1 + 1320mm^2 x 1 = 2412mm^2 = 3.74"^2
The force you would calculate from those areas though is the single directional force imposed on the pistions. The clamping force of the caliper and the one you want to use to work out braking forces is in fact double the single directional force you calculate using the piston areas for one side of the caliper. This is the same for opposing piston or sliding calipers. Work out area for one side of pistons. Work out single directional force and then double it to get clamping force. I think this is what your calculator does too.
