Hand Brake Master Sizing Explained

[SIC Nate]

The numbers refer to millimeters - the first number is the bore diameter size (area that pushes the fluid), the second number is the pivot distance between the pistons push rod center and the pivot center.

The main difference in master cylinder size as it relates to our use:

- 19 and 20 mm masters are typically used to drive (2) four piston calipers
- 16mm are typically used on a singe four piston caliper (some bikes only have 1 disc)
- 13mm is typically used on a one or two piston caliper

This is due to the amount of fluid that the master's bore is designed to move to the calipers.

What does this mean to us? well, for handbrake purposes, you would match the master size to the handbrake caliper size as appropriate or choose a different size based on the feel that you are looking for.

i.e. A Large master used on a small caliper will have a very hard feel with little lever travel as it is trying to move a lot of fluid and has nowhere to move it to. Conversely, if you used a 13mm master with a four piston caliper, you will have a very soft lever with lots of travel (which some may like better as more variable control).

[JohnnyP]

Quote:

Originally Posted by SIC Nate The numbers refer to millimeters - how wide by how deep the bore of the piston in the master is (area that pushes the fluid)

That is partially correct, the first number is the bore diameter size, the second number is the pivot distance between the pistons push rod center and the pivot center...Not the bores stroke...

[SIC Nate]

Quote:

Originally Posted by JohnnyP That is partially correct, the first number is the bore diameter size, the second number is the pivot distance between the pistons push rod center and the pivot center...Not the bores stroke...

You are the master of all knowlege! Thanks for bringing better info
I'll edit the first post

[JohnnyP]

Quote:

Originally Posted by SIC Nate You are the master of all knowlege! Thanks for bringing better info I'll edit the first post

No problem if you look at the new RCS brembo masters, they allow you to change the pivot distance by turning a screw. So if you by a 19RCS it can be both a 19x18 or a 19x20 just by turning a screw...

[chino12]

i was always lookin for a clear explanation on this subject

great thread buddy

[WHEELIE]

Good Thread Sic...

[SIC Nate]

Because I have explained my preference a couple times, I'm going to post it here as well.

Having tried both the Magura 13 and the Brembo 16x18 with a single 4 piston HB caliper, I personally prefer a 16mm. A 13 on the HB gives lots of progressive control, however it is harder to tell where the wheel lock up point is. I like to have the lever get progressively harder and then very hard/stop at the lock up point. The 13's will continue to pull past the wheel lock up point without much difference in lever feel.

This is just my preference. Plenty of people like 13's.

[johnb]

Hey sorry for jacking this thread. Im just wondering what size is a standard 03 636 front master? Would it be good enough to run one for a 8 piston Hb setup? Any info would be great. Cheers

[SIC Nate]

Quote:

Originally Posted by johnb Hey sorry for jacking this thread. Im just wondering what size is a standard 03 636 front master? Would it be good enough to run one for a 8 piston Hb setup? Any info would be great. Cheers

The OEM 03-04 636 front master is 14mm bore.

It is designed to run (2) 4 piston calipers, however I would recommend using a 05+ radial master from just about any manufacturer. You would like the response much better.

Radial masters have the piston travel the same direction as the lever so your input is transferred directly to the caliper.

Older non radial masters have a pivot with the piston travel sideways.

[SIC Nate]

When talking about the 'feel' of the brake system, the key to the whole issue is the master cylinder piston size. Smaller will give higher psi at the calipers, but will have more lever travel. Same size will do the same psi. Larger will have less psi at the calipers with less lever travel, so to get equal power you have to squeeze harder.

The lever ratio will play a factor too. The length of the lever from the pivot to the plunger rod as compared to the length of the lever where it is gripped will make a difference too.