Leverage Ratios/Choise of Master Cylinders

[Scotchmist]

Hi all,
Does anyone know the best leverage ratio for a Yamaha blue spot caliper? Based on my (possibly shaky) calculations I've worked out the following ratios based on different master cylinder bore sizes:

10mm MC = 32.58:1
11mm MC = 26.92:1
12mm MC = 22.63:1
13mm MC = 19.28:1

Does anyone have experience of any of these MC sizes?

Thanks.

 

[Crashomon]

See here:
http://www.vintagebrake.com/mastercylinder.htm

 

[Scotchmist]

Thanks for the link. The website seems a little ambiguous. The section about "two piston opposed calipers" apply to both 2 and 4 pot calipers?

 

[Crashomon]

if you look on the left side of that chart, he indicates 'active piston'

28mm {single pot}
28mm (2) {2 pot}
28mm (4) {4 pot}

then from there, you scan over to the correct ratio.

As he noted:
"For 2 piston opposed calipers, I like ratios in the 27:1 range, feeling some line and caliper flex. For a firmer lever, use 23:1"

Does that help?

 

[Scotchmist]

I think it does. I just wasn't clear whether the leverage ratio mentioned for 2 pistons opposed calipers was tthe same for 4 piston opposed calipers I.e. 4 pots. 4 lots are listed in the table but not mentioned specifically in the text.

 

[Crashomon]

The author notes :" It has been my experience that there is a "sweet spot" in the range. I like ratios in the 27:1 range-2 finger power brakes, feeling some line and/or caliper flex. 23:1 is at the other end of the spectrum-firm."

FOR SINGLE PISTON: Single piston calipers are much happier in the 14:1 to 12:1 range.


Now, by extrapolating the 1/2/4 pot lines on left, you can navigate to the right to find the sweet spot for your given Caliper Size.

Example:
48mm/1 pot's sweet spot with a 13mm OR 12mm M/C (based on 14:1 to 12:1 ratio listed above)
48mm/2 pot's sweet spot is with a 13mm or 14mm depending on your 'feel' preference.
48mm/4 pot's sweet spot is gonna be 19mm. (if 27:1 to 23:1 ratio holds)

Generally speaking: if you use 'stock' or 'close to stock' ratios, you should be OK.

 

[Crashomon]

Okay, I'm ignorant about blue spot brakes (my bad); just realized what they were through a quick search on here.

Even though the chart is for OLDER brakes (pre-2000 I believe)
You CAN extend that chart downward to include 65mm/4 pots to determine best ratio M/C to use...

 

[Scotchmist]

I've worked out the specific ratios for blue spots and it should be fine. Thanks for your help.

 

[Crashomon]

Excellent! Cheers!

 

[pereiracycles]

I have a single blue spot caliper on my bike and am using a 12mm MC from a Ninja 250. Works great! Let me know if you have any questions about my setup.