16 or 19mm master cylinder?

[Randy Grein]

Matter of leverage, total leverage. That is, figure the mechanical  
advantage of the lever itself and then multiply it by the mechanical  
advantage of the MC over the slave pistons. Piston mechanical  
advantage is calculated by surface area of ALL pistons, not just the  
number of pistons - and that means if there are different size slave  
pistons take that into consideration.

Calculating the mechanical advantage of the lever itself is somewhat  
harder, but not too bad. Measure the pivot-finger distance and divide  
that by the pivot to piston contact point distance. Obviously your  
normal hand position is important; moving the lever mount can make a  
20-30% difference in mechanical advantage.

Randy Grein

On Jun 18, 2011, at 8:44 PM, matthew patton wrote:

>> Nope, the opposite. A larger m/c will deliver less braking
>> power for the
>> same lever force applied. In this case, braking force will
>> be about 30%
>> less.
>
> i'm confused. then why are single or double pistons mated to 13mm  
> MC, 4 piston to 16/17mm and 8 pistons with 19/20mm MC?
>
> Yes, for a given force applied at lever, the smaller MC plunger  
> means more pressure/mm^2, but the bigger the ratio between caliper  
> and MC pistons, the more travel needed at the MC to move the caliper  
> pistons the same amount.
>
> isn't the reason for the aforementioned pairings to make sure you  
> don't run out of lever before you get enough pressure into the  
> hydrolics?