New master cylinder help (brake swap)

Alright, so im running a custom brake setup on the RD project, and ive been trying to research how to select the correct master cylinder setup but I really havent found anything on here or the Googles. Hoping an expert can help clear the muddy waters for everyone.

My case, running a single 2 piston FZR1000 caliper

I have found the follow information
Piston diameter to master cylinder size http://www.vintagebrake.com/mastercylinder.htm
Very generically lumped master sizes http://rg500delta.com/RG500_chassis_files/master%20cyl%20bore%20sizes.pdf

So, step 1, measure the diameter of the pistons. Having multiple, and the two being of different size, how do you go about doing this?

Step 2, figure out the ratio you need. This guys talks about 2 piston opposed calipers and single piston calipers. I think he means 27:1 if you are running duel disk, and 14:1 if you are running single disk. Can anyone confirm?

Step 3, find a master cylinder. You can use the link above, to get general on used masters, but they are lumped into three categories so its give or take.

The ratio chart is all based on are of the MC piston to the caliper piston. Take the area of each piston you plan on moving with that MC, add them up and figure out what size MC you need to get the ratio you want. You could make a sheet in Excel with your caliper piston area as the known value and plug in different MC piston sizes to see what ratios you get, then pick the ideal one.

I thought FZR1000s had 4 pot calipers, early TZR250s have one caliper and disc that are the same as FZR1000 ones, I think the TZR had a half inch master cylinder, but 12-13mm will be right, 12 a little soft 13 a bit hard, 14 will be much too hard.

julian.allard66 said:

I thought FZR1000s had 4 pot calipers, early TZR250s have one caliper and disc that are the same as FZR1000 ones, I think the TZR had a half inch master cylinder, but 12-13mm will be right, 12 a little soft 13 a bit hard, 14 will be much too hard.

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Maybe you are right, two on each side of the disk. Tonight i'll grab the caliper and see what I can do about getting measurements of the pistons.

I wouldn't overthink it - you want a 14mm MC.


Or a radial one.....but I'm not sure if they use the same bore size (I think 17mm in a radial is the equivalent of a 14mm normal MC).

julian.allard66 said:

I thought FZR1000s had 4 pot calipers, early TZR250s have one caliper and disc that are the same as FZR1000 ones, I think the TZR had a half inch master cylinder, but 12-13mm will be right, 12 a little soft 13 a bit hard, 14 will be much too hard.

Click to expand...

From looking at pics, the 76-78 TZR does seem to run a single side of the FZR setup. According to that chart, that gen TZR runs a 14mm which goes along with what hilley said below

Alright, so I measued out the pistons, one is 35mm the second is 37mm, and there are another set on the other side. So 4 pistons total, with a total of 144mm