Topic: Master Cylinder ratio - What is ideal?

[batdan]

I destroyed the original master cylinder doing something stupid and I'm thinking about overhauling the front brakes. The thing is I'm not certain the original master cylinder bore is ideal for the application. According to this webpage http://www.vintagebrake.com/mastercylinder.htm they suggest a master cylinder piston area to caliper piston area ratio of 14:1 to 12:1.

For the stock single piston caliper of 14mm and the 38 mm caliper piston  the ratio would be

38^2/14^2 = 7.37

far outside the suggested range. The suggested master cylinder according to the chart would be 10 or 11mm!

If I had a dual caliper setup with what I think is a standard 16mm master cylinder the ratio would give

(2*38^2)/16^2 = 11.28

This is much closer to the suggested 12:1 to 14:1. To get this ratio I would need to get an 11mm master cylinder. I can apparently get these from Yoyodyne (http://www.yoyodyneti.com/Category.aspx?CategoryID=3006) along with aluminum banjo bolts and stainless steel brake lines and other goodies.

If I understand correctly the big reason to get multiple calipers has more to do with getting more pad area for reasons of brake life and better handling of heat and whatnot and less to do with overall braking power and feel.  So would this change in ratio give me a feel and braking power more inline with the dual caliper set-ups or is it a bad idea?

 I remember seeing site with a Goldwing where the owner suggested that first generation motorcycle disc brakes were too conservative with the ratios and the a smaller master cylinder would improve brake feel and power and I think I got it from this site but I can't find it again.

Anyway I plan to buy an 11 mm (or maybe 12mm if I feel conservative) Brembo Master Cylinder and new braided brake lines/banjo bolts/bleeder sometime soon from Yoyodyne unless someone can give some compelling reason not to.

[Ricky_Racer]

Great link, Daniel.  Thanks! RR

[batdan]

Bump so someone who knows something about this may see it....

[fastbroshi]

  Thought I'd comment on this, though it's been a while, given the recent posts on improved braking an such.  I spoke w/ Fred @ Yoyodyne and he added that setups like ours tend need a different ratio versus a system that has a fixed backing and not a pivoting "arm". 
 

[moham]

  Thought I'd comment on this, though it's been a while, given the recent posts on improved braking an such.  I spoke w/ Fred @ Yoyodyne and he added that setups like ours tend need a different ratio versus a system that has a fixed backing and not a pivoting "arm". 
 

Could you be more specific? Do you mean a ratio different from the 12.0-14.0 suggested by the Vintage Brake site for single caliper set-up? Thanks, I've spent the last week or so digesting all of this braking info so I'm curious to hear what Fred has to say.

[fastbroshi]

Said he spent some time talking to the Brembo engineers (take it with a grain of salt, could be tooting his horn).  From what I took from our conversation, our systems kinda of act like a dual setup already, so you can just double the ratio we already have for a single caliper, which would give us 14.74, slightly over the optimum range.  Maybe it's accounting for our oh-so-wooden brakes. 
   He added that if the ratio were truly 7.37, our brakes would be super mushy. 

Given a 14mm master -
caliper piston: 38mm

38^2/14^2 = 1444 / 196 = 7.367   

or roughly doubled ratio with our system, 14.72.

Given a 15mm master -
38^2/15^2 = 1444 / 225 = 6.417

or roughly 12.8.

   This would put us almost smack dead in the middle of the 12-14.0 range stated on the chart you cited.  I like this one for the adjustable lever. 

http://www.yoyodyneti.com/ProductInfo.aspx?productid=10.6870.18

   But I defer to those who're really experienced with this stuff.

[moham]

He added that if the ratio were truly 7.37, our brakes would be super mushy. 

That's an interesting point, because I wondered about that number myself when calculating according to the chart (or formula). That 7.37 would seem to indicate a really sub-par performing brake, and it seemed crazy that the stock set-up would be so far off optimum (insert qualifier here about production/manufacturing methods, 70s technology and Honda's need to appeal to wide spectrum of riders, etc.)

But I defer to those who're really experienced with this stuff.

Well-said. My problem is I'm a relatively new rider (70's era bikes or otherwise) and my practical knowledge is next to nil. I know what my re-built 750K8 brakes feel like but have nothing to compare them to (at the moment).  The other issue seems to be a large degree of subjectivity when people describe their experiences. I would have to agree with you and defer to those with the experience to judge such fine mechanical matters.

Thanks for posting your findings. I can speak for myself and say that I will use all of the info mined here in these brake topics to set up my 550 project with "vintage-style brakes with modern feel/performance"

[fastbroshi]

   My whole quandry is I'd like to upgrade my brakes too, but I don't want to spend $1,000 to do it, i.e. grafting on a new front end.  I realize that figure may be high or low.  I think others will agree the biggest hurdles are the rotor and caliper.  The master, lines, pads, etc. can be changed w/ modern stuff easily. 
   Someone do a writeup on what front rotor and caliper you switched for god's sakes.  No whole front ends allowed.  This means you, FunJimmy.

[Joksa]

The hydraulic ratio is not the whole truth as there is also mechanical lever ratio also so isn't the overall ratio product of both ratios? 

[fastbroshi]

   I think that's going to vary little between the manufacturers.  Besides, if it were too far out of whack you'd be able to tell by looking at it, i.e. can't get your hand around the lever comfortably.  I've seen aftermarket shorty levers that I think accomplish the same thing, just make it real hard to squeeze the lever throughout it's range. 
  The lever I linked above adjusts; would this address what you're talking about.

[Joksa]

 The lever I linked above adjusts; would this address what you're talking about.

The adjustment affects only how far the lever is.

MCs with adjustable ratio are far more expensive
(eg. ISR  http://www.bikehps.com/isr/ISR_Master_Cylinder_Lever.jpg ).

[fastbroshi]

   I am just amazed at the number of billet products out there nowadays, and for the most part I doubt they do their jobs better proportionately to price.  They do LOOK nice though.  I see that one does have some extra adjustment knob on the lever.  Wouldn't this be used to fine tune, rather than setup, your braking feel?

[754]

I am not up on brake theory.


 I am thinking the only thing the adjustable lever does is fit in your hand better, and maybe bottom out on grip if so desired. More or less setting freplay for your hand.

 I constantly see people searching for better master cylinders on sohc 4,s. I used to run stock drilled dual disc with stock master cylinder and braided -3 lines. I did not mind the way it felt, sometimes would only use 2 fingers for braking & did not feel I was missing anything... But keep in mind I have never ridden anything modern.

As far as the billet performing better because of price, I dont think that is a reasonable expectation.

The main difference in  construction is it is carved from a single piece, and involves much more time and material expense, but can be produced in smaller numbers. When using forgings your material cost per master cylinder comes in way lower, but only due to large numbers absorbing the high charges of initial setup... this is followed by drastically reduced finishing machining times.

[tygrant]

I just put a mic on an old piston i have and its a 42 mm diameter...came of a 75 550 f- is that right?

[754]

If the  lever has a ball end pushing the master cylinder plunger, then the ratio would be getting changed on the other end.. by altering the distance of the pusher pivot to the handle pivot??..is that correct

[fastbroshi]

754, better bust out MS Paint and make a drawing for this one.

[754]

I could not make out any of that on the drawing, just a cylindrical shape  outside of the end of the piston. Then the fact that they showed the arc of lever movement probably threw me off more.

I have an 05 R6 MC at the shop will take a close look at it.. probably already did but 4 truckloads of used bike parts has passed over my hands since then! And MEMORY is like COMPRESSION.. ..eventually it goes down....