Brake ratios

[morgy]

Hi

I am looking for a new brake master cylinder and possibly a clutch master, Some seem to specify a ratio, I will either be fitting Tokico twin 4 or 6 pots. any idea if i have to spec a certain ratio.. 

Thanks 
Mark 

[dusty350]

Hi Mark
I have 4 pot Rgv Tokico's on my orange hybrid and I use the Rgv 14mm master cylinder. The white bike has 6 pot Beringers and that also has a 14mm Nissin cylinder as per Rgv. My thinking is that if Suzuki spec'd the 14mm master cylinder for the 4 pots then that should be good. Not sure about the 6 pots though - I will let you know when that system is bled and working !!

Dusty

[oldelsieboy]

Jan 4, 2018 15:15:52 GMT 1 morgy said:

Hi

I am looking for a new brake master cylinder and possibly a clutch master, Some seem to specify a ratio, I will either be fitting Tokico twin 4 or 6 pots. any idea if i have to spec a certain ratio.. 

Thanks 
Mark 

Does this help?

www.vintagebrake.com/mastercylinder.htm

OEB

[morgy]

Jan 4, 2018 17:45:53 GMT 1 oldelsieboy said:

Jan 4, 2018 15:15:52 GMT 1 morgy said:

Hi

I am looking for a new brake master cylinder and possibly a clutch master, Some seem to specify a ratio, I will either be fitting Tokico twin 4 or 6 pots. any idea if i have to spec a certain ratio.. 

Thanks 
Mark 

Does this help?

www.vintagebrake.com/mastercylinder.htm

OEB

I came across that but didn't make much sense, LOL 

[bare]

? Not that tricky, it does take a bit of time to digest. But the info ..is.. there.
The claim is 27:1 is "good" ratio Well then Highlight all the identified 27:1 ratios.. Actually anything reasonably similar is best to hope for.
Then sort those for the size/diameter/number of the Caliper pistons being operated.. then read what sized Master cyl bore is appropriate.
The correct Ratio makes a World of Difference in braking.
Also don't be forgetting that your tires need to be fully adequate to the demands of a Big Brake setup.. or You might experience 'religious moments' along with a locked front wheel

[morgy]

Thanks Bare...

I was looking for 6 pot but this table does not have them... I did find a formula somewhere

He does talk about different ratios for single piston and double piston so would a ratio of 27:1 be what i would be looking for with twin 6 pots or twin 4 pots..

[morgy]

I found an interesting thread on another forum...

Copied and pasted below.. Can anyone open the XLR file as i can't open it on my Mac...

Many have asked me to help with changing from a conventional axial front master cylinder (MC) to a radial, and in trying to give accurate information I came up with the following spreadsheet to help determine what piston size radial MC would be appropriate. The reason why there is so much confusion is the basic setups of the two types are quite a bit different: the axial units typically use a smaller piston size than the radials, and a lower mechanical leverage ratio at the lever than radials.

For example, my 2002 Honda 919 with stock master has a 14mm piston and the lever pivot to piston distance is 25mm, while the pivot to hand distance is ~ 90mm (When divided it is called the interaxis ratio). When the total area of all eight caliper pistons (30.15mm and 27mm) is divided by the area of the MC bore it gives a hydraulic ratio of 33.429:1, which when multiplied by the interaxis ratio produces an overall leverage ratio of 120.34:1. This is on the low side of typical for modern sintered brake pads. When I decided to switch to a radial MC for a variety of reasons, not the least of which being a desire for a slightly higher ratio for less effort at the lever and a wider engagement band to make holding the brake just this side of locking easier, I crunched the numbers for an overall ratio of ~130 - 135:1, and came up with a MC bore size of 17.5mm (actually it's 11/16ths, or 17.4625mm). Fortunately this is a size used by all years of the CBR1000, and a couple of Kawasakis. Installation of a MC obtained from a seller on EBAY confirmed the validity of the calculation -- slightly decreased lever effort, and better control near locking up.

On the subject of what ratio is desirable, and what to do if the ratio you want does not match up to an available master cylinder piston diameter: shoot for the next larger size piston and adjust the ratio using the only other parameter available to you -- the Master cylinder lever pivot to finger distance. For an example the numbers on the spreadsheet are for my 919. Change the master cylinder piston diameter to 18mm then go down to the pivot to finger parameter and change it until the overall ratio matches. Once you know approximately where to mount up the master cylinder it is easy to vary the feel on the road (well, parked next to the road) by moving the MC toward or away from the throttle.

Another factor to take into account is the coefficient of friction of the brake pads. Pad manufacturers do not make this information available for obvious reasons, so you have to go by feel here. If you are running brand X pads and like the feel they give with the stock MC enter the appropriate numbers in the spreadsheet for your system to get the stock ratio, then change the interaxis pivot to piston / pivot to finger and piston diameter numbers for the MC you want to run. If, however, the pads are too sensitive or "grabby", decrease the stock ratio by about 5% to start. Conversely, if they have adequate power but take too much effort at the lever increase the ratio by 5%. Then vary the pivot to finger number to obtain the desired ratio. You get the idea.

FYI: The typical range of ratios for modern brakes are from ~115:1 to 145:1 or a little more. Lower than 115 will give a lever that pulls back a short distance then feels rock hard, but takes too much effort at the lever to stop. Higher than 145 to 150 will take more lever travel to engage the brakes, but will require less force at the lever, usually feeling too sensitive when braking.

The spreadsheet: written in MS works, will also open in Excel.
www.dropbox.com/s/8arv9ncbyu...ulator%201.xlr
It will work for up to 6 pistons. It will also work for single acting calipers as while there are pistons on only one side, the rear wall of the bore the pistons operate in acts as a second piston, moving the entire caliper body to apply force to the inside pads. They are calculated in the same manner as the double acting calipers.

[JonW]

I get a 404 error with that link :/

[kevm]

Im using R6 radial calipers with a R1 master cylinder why not use the original master cylinder then you know its right.

[morgy]

Jan 14, 2018 22:32:30 GMT 1 kevm said:

Im using R6 radial calipers with a R1 master cylinder why not use the original master cylinder then you know its right.

I'm going Or have gone Hydraulic clutch... So i wanted a set of Matching Masters.. I've bitten the bullet now anyway but wanted to check i've got the correct brake master cylinder bore before i put fluid in it and find it's not right.. 

[morgy]

Jan 14, 2018 22:23:32 GMT 1 JonW said:

I get a 404 error with that link :/

Oh not sure what's going on there... 

Anyway here is a link to the Thread... 


www.wristtwisters.com/forums/f322/calculator-for-finding-the-proper-size-radial-master-cylinder-48345.html