Found Great Brake Master Cylinder vs. Caliper Sizing Info.

While reading a post on a Ducati forum noting issues with using Panigale (1199) calipers with other master cylinders; I came upon the following general info. concerning MC vs. Caliper sizing. Enjoy! :up:

When you design a hydraulic system it's important to have good feedback from the lever as to how much lever force to apply to achieve a desired braking rate. Having good feel, sensitivity and control is the major factor influencing braking quality.

The main factor in designing good braking modulation characteristics is the ratio of the total area of the caliper pistons to the area of the master cylinder.

The Panigale calipers have a total piston area of 5655 sq. mm and has a master cylinder area of 201 sq. mm. This gives a hydraulic ratio of 5655/201 = 28.1.

The RCS brake master cylinder has an area of 284 sq. mm. Used with the Panigale calipers you get an hydraulic ratio of 5655/284 = 19.9.

A general design rule-of-thumb for twin rotor brake systems is as follows:

30:1 - soft feel
27:1 - sweet spot for design
23:1 - firm feel
20:1 - wooden feel

 

There is also lever ratio to change feel.

 

^^ Great Info. I've seen a lot of posts complaining about feel etc. with after changing calipers and or MC's. I hope all the above will help with those issues.

 

Good info, thanks. Do those ratios apply to single disc setups as well if the equation takes into consideration all calipers piston area?

 

how do you measure the area of the master cylinder????

by the way my setup came out a 22.65, and its on the firm side for shure...
RCS with brembo calipers with 32mm of piston.

 

The dude is using the wrong term. Its not area....area is the measurement of an object in a single plane.

He needed to use the term volume. It helps make it sound like he knows what he is talking about. It being on a Ducati forum it means there is a 50/50 chance he doesn't know crap.

 

http://en.wikipedia.org/wiki/Volume

The master cylinder is easy. The caliper no so easy.

 

jajajaja.
I just calculated the area based on the 8 pistons 32mm and took the master since I hav a RCS

 

The dude is using the right term.

The area (πr^2) of the piston surface in the MC (and inversely, the calipers) is directly related to the amount of fluid pushed per a given length of pull on the lever and thusly the distance the pads are pushed for that distance of lever pull; directly determining feel.

Your addition of a third dimension (representing the length that either the MC piston or caliper pistons move) to calculate volume presumes some distance of lever pull and caliper movement to calculate area and is unnecessary to determine the ratios referenced.

 

You have to know the diameter of your piston inside the MC, then plug it into the equation for the area of a circle.

 

The calipers are exactly the same process. Use the same equation for the area of a circle using the diameter/radius of one piston and multiply it by the number of pistons you have.

It's only slightly more tedious if all of your caliper pistons are not the same diameter.

 

I think chuckbear is correct, we dont need the 3rd dimension...

Also I have the same master as he has and used his number.... also the final number also corresponds to what I fell at the master, a firm lever.

 

Thanks for sharing this info btw. It's something that's talked about often, given how different setups give a different feel at the lever, but I've never seen something that puts it together so concisely.

 

That chart has been on www.vintagebrake.com since the day after Al gore invented the internet.

The chart does NOT reference lever ratio.

Variable leverage ratio master cylinder design like the Brembo 19RCS allows the rider/mechanic to change teh feel of the brake as well as the amount of brake being applied with the same lever pull if traction conditions change. (i.e. dry to wet.)

The adjustability of that master is the lever pivot distance from the piston centerline, NOT a magical change in master cylinder bore diameter as I have heard someone say on one forum.

 

Well lets do some math...

2009 GSXR1000 Calipers = 6459.114495780615

(4) 30mm pistons = 4 x 706.8583470577034 = 2827.433388230814
(4) 34mm pistons = 4 x 907.9202768874502 = 3631.681107549801

2827.433388230814 + 3631.681107549801 = 6459.114495780615



20.6mm x 14mm Beringer Master = 333.2915646193412

6459.114495780615 / 333.2915646193412 = 19.37977189178999

I guess that puts me at woody...



Let's try with a Brembo 19mm x 18mm = 283.5287369864788

6459.114495780615 / 283.5287369864788 = 22.78116343490305

OEM GSXR set up, I guess that put us at almost Firm Feel...



Let's see what we can get from a 16mm Master = 201.06192982974676

6459.114495780615 / 201.06192982974676 = 32.12500000000001

That put us at way too soft...



Can someone verify my math... I used a calculator...

Luis



Edit OEM R6 - 5117.654432697773 / 201.06192982974676 = 25.45312500000001

R6 with Brembo 19mm x 18mm - 5117.654432697773 / = 18.04986149584488

 

Actually damn my brain didn't work on that one. Yes calipers just as easy...if you know the stroke they will go through.

 

Don't overthink it. :up:

 

Ok already, simple hydraulic ratio, with a simple lever used as the source of force. The math was done back in the 1600's, the Greeks and Egyptians probably had it too. Are we are still confused by this...

Google "Pascal's law" and "mechanical advantage", something might be found.

Doomed to repeat the same failures...

 

Looks right to me. I got the same for Brembo 19 and R6R calipers, and that's my current setup. With 16mm master it would be 25.45.
For 19x18 master calipers with 34mm pistons (7263,36) would be nice - 25.62

 

There is a Beringer 17.5mm x 12mm - 240.52818754046854

With your R6R Calipers...

5117.654432697773 / 240.52818754046854 = 21.27673469387755

With 09 GSXR 1000 Calipers...

6459.114495780615 / 240.52818754046854 = 26.85387755102041


Now the question is, Will it move enough fluid? Or will the lever move all the way to the grip?

Luis