yamaha master cylinder

Jim Stewart js at strappe.com
Sun Jul 11 12:09:53 PDT 2010

Gregory Maust wrote:
> Technically you're dealing with pressure. Pressure is force divided by area
> (P = F/A). A smaller diameter means a smaller area, and thus less force is
> needed from the lever to produce the same pressure. Conversely, a larger
> diameter's increased area necessitates increased force to produce the same
> pressure.
> Leverage is largely an issue of lever length (or distance from axis of
> rotation), and should be constant so long as your hand is at the same spot
> on the brake lever. The improvement in braking systems have let us use less
> and less leverage to get the same results, hence the stubby levers and
> one-fingered braking.
> Sorry, I can't help myself sometimes :P

I suppose I shouldn't have said "leverage" when I meant the ratio of 
forces, but I did because everyone understands the term. Or so I thought.

As long as we're being technical, there are three factors that determine 
the amount of lever force for a given braking force (ignoring lever and 
piston friction):

- The leverage ratio of the (ahem) lever can only be approximated 
because it depends on the point on the lever that the force is applied, 
  and usually there is no single point. I usually choose the position of 
my middle finger. The ratio of (the distance from the middle finger to 
the pivot) to (the distance from the pivot to the short end of the 
lever) we can call the lever ratio. (Parentheses added for clarity.) 
People often use the actual length of the lever from the pivot, which 
leads to a largish error.

- The ratio of the area of the master cylinder to the combined areas of 
the caliper pistons. This is the big one.

- The ratio of the tire's tread radius to the distance of the brake 
piston centers from the axle. This is where a large rotor makes a big 

Multiply these three together and you get the overall braking ratio.


I proofread this twice. Hope I didn't screw it up!  ;-)


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