View Full Version : Caliper / Master Cylinder bore sizes.

03-19-2012, 9:34 PM
Did a search and cant get any solid info.
Im going to run a single 4 piston caliper up front, its off of a 02 Honda RC51.
The original specs for the donor bike are as follows.
2002 Honda 954-SP2 RC51
Dual, 4 piston front calipers with a 32/30mm bore.
Paired with a 17mm Master Cylinder.

Since Im just going to be using 1 of the 2 calipers should
I still try to shoot for the original 17mm master cylinder?
Or do I need a smaller bore size to get around 23:1 / 20:1

03-20-2012, 7:30 AM
Im not familiar with american calipers, if the bore size from some american
Style caliper is comparable to what I have I could use a 9/16 master?

03-20-2012, 7:42 AM
Man, I am glad you asked this question. I don't understand 2 caliper vs. 1 caliper bore size....

03-20-2012, 9:54 AM
5/8 I think would be ideal. 9/16 would work, anything larger will working best with duals. Right now I am using a 17mm with a single 4 piston on the rear & it does the job.

03-20-2012, 10:27 AM
I run a Brembo 4 piston goldline caliper. It takes a 13mm MC. If you run a 17mm MC for a single 4 piston designed for dual 4 piston calipers, you're going to get a "wooden" lever.

My caliper came off a ducati monster with dual 4 piston calipers, and Brembo standardized this setup with a 16mm MC.

Your best bet would probably be a 1/2" MC (12.7mm), or a 13mm. A 9/16" bore is roughly a 14.28mm conversion, and in my opinion, a little too big for good lever feel.

Mikes XS has a few different MC options.

Wilwood makes a badass 1/2" MC that's only 7.5" total length, but you can only source the unit from a supplier called porterfield enterprises (Willwood's site says they only make 5/8, and their customer service also says they don't offer a 1/2"). This MC takes a 3/8 short banjo but 10mm banjo brake line fittings are designed to work with either 3/8" or 10mm banjo bolts. Mixing an American MC with a metric caliper is easily done.

You could also track down some sport bike Nissin MCs. Not too sure on exact piston bore size, but a lot of guys use these if you're planning on running a tiny reservoir.

The Brembo MC I have also used is a new OEM replacement from Yoyodyne. About 10.5" long, but man, that MC with my goldline caliper will put me over the bars if I'm not careful.

You can get all this info from Yoyodyne. I think the dude's name is Fred.


03-20-2012, 3:40 PM
You can mix them but what you get into is... If you run a Large(r) Master Cylinder, say a MC for a duel disc brake with a Single Disc what you get is Very Little Movement Of the Brake Lever. If you run a MC designed for a single disc brake with a Duel Disc what you get is A Lot Of Movement of the Brake Lever Before you have brakes.

Harley wise a 5/8"s bore MC for a Single Disc Brake. The 11/16" MC's are for Duel Disc Brakes.

It's not going to screw anything up it will just effect how far the brake lever moves before you actually have brakes.

Make any sense?

03-21-2012, 2:34 AM