spectrum Posted February 23, 2013 Report Share Posted February 23, 2013 I need to replace front master cylinder on xs650 yamaha. Cylinder that's on is for clip ons and wont sit right with flat bars. I've looked on interweby and everyone as different opinions on correct ratio. How do I work out ratio ? or are there any reliable online sites you can trust ? Link to comment Share on other sites More sharing options...
marcaztls Posted February 23, 2013 Report Share Posted February 23, 2013 http://www.vintagebrake.com/mastercylinder.htm Link to comment Share on other sites More sharing options...
dansp1 Posted February 23, 2013 Report Share Posted February 23, 2013 I spent a while on that site working out ratios and came to the conclusion that it is more complicated than simply the hydraulic side of it, since there are different leverage ratios involved. My SP1 has a 19mm m/cyl standard and i am using a 5/8 bore ISR unit, all singing and dancing, believe me it is not lacking in power or feel although it is well outside the 27:1 ratio recommended on the site mentioned........... Link to comment Share on other sites More sharing options...
spectrum Posted February 23, 2013 Author Report Share Posted February 23, 2013 Had a look at the vintage brake site and for twin disc he reckons aprox 27-1 then another site I looked at said 15-1 for same application ? Link to comment Share on other sites More sharing options...
porter_jamie Posted February 23, 2013 Report Share Posted February 23, 2013 Smaller mc increases braking force and lever travel for same lever effort. And vice versa. Bigger caliper piston reduces lever load for same braking force. (Same thing as above) Smaller hydraulic cylinders at both ends but same ratio increases line pressure and volumeric expansion losses in the hose and vice versa but you have a larger seal in the bigger scernario too so you might get more friction/hysteresis. What counts is the overall lever to pad ratio. Link to comment Share on other sites More sharing options...
toosmooth Posted January 16, 2014 Report Share Posted January 16, 2014 So, if I have a pair of sliding pin calipers with a 30 and 32mm piston in each (area of all 4 pistonsadded up = 3022mm2) and I have a master cylinder size of 19mm (with an 18mm ratio? it's from a 999 Ducati) I get a "feel" rating of just under 12. The internet (god bless it, and all it's perceived wisdom) would suggest everything points to this being a bit overkill, and as it's a 999 Master cylinder on deauville brakes, maybe thats true. But it's got to stop 230kg of 1170 Katana + 80kg of rider on a racetrack, so power over feel isn't a bad starting place. Any thoughts? As with the whole bike I'm in suck it and see mode, but it'd be good to have a bit of thought applied to it up front, help shape the direction if needed. cheers! Link to comment Share on other sites More sharing options...
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